Although I have thoroughly enjoyed doing the research and writing for this labor of love, my private business venture (ISLANDER VIRTUAL ASSISTANT) is making increasing demands on my time (and energy!), and so I’ve decided that this will be the last post for this blog.

The individual blog posts (except for the first three 2009 posts, which were embarrassingly poor) will remain on this blog site. Their individual hyperlinked titles are listed below (oldest to newest). Mouse-click on the title to go to the selected post.

• The Plant Life of Maui’s Urban Beaches
• Bamboo: The “Grass” on Maui is Fifty Feet Tall
• Maui’s Beautiful Weeds: Lantana camara
• Maui’s Beautiful Weeds: The African Tulip Tree
• Maui’s Beautiful Weeds: Koa Haole
• The Blue Jacaranda: Spring has come to Maui
• The Plant Life of Maui’s Urban Beaches
• Maui’s Drylands Survivors
• The Silk Oak (Grevillea robusta): When Good Trees Go Bad
• Maui’s Morning Glories: Part I – Ipomoea indica, the Blue Morning Glory
• Maui’s most common Morning Glories, Part 2: Ipomoea pes-caprae, the Beach Morning Glory
• Maui’s Prickly Pear Cactus (Opuntia ficus-indica)
• Kiawe (Prosopis pallida): Hawaii’s Tropical Mesquite
• The Coconut Palm
• Ironwood (Casuarina equisetifolia): The Pine Tree’s Evil Twin lives in Hawaii
• The Basic Science behind the Seeds and Fruits of some Common Hawaiian Plants
• A Mean Little Weed from Madagascar: Mother of Millions (Kalanchoe delagoensis)
• Ginger Plants (Family Zingiberaceae) Commonly Seen In Hawaii
• Hau (Hibiscus tiliaceus): This native Hawaiian Hibiscus is a real survivor
• ‘Ohelo (Vaccinium reticulatum): The Fruit of Maui’s Sacred Native Shrub was the Gods’ Sweet-Tasting Gift to Early Hawaiians
• Beach Naupaka: How a Nice Plant gets a “Bad” Name — What do we call it, “Scaevola sericea” or “Scaevola taccada”?
• Koa Tree (Acacia koa): Two kinds of leaves on one tree confuses the tree-spotter
• Banana Poka (Passiflora tarminiana): Look out for the vines!
• Clidemia hirta: Koster’s Curse Lives On In Hawaii
• In Hawaii, an Epiphyte Cactus says “I am NOT a Parasite!”
• Cuscuta sandwichiana – Dodder: a cross between Count Dracula and Silly String

I hope that these posts will continue to be useful to those of you interested in Hawaii’s botanical heritage.

Malama ‘aina, a hui hou kākou!

Mike Garrison

Kihei, Island of Maui, Hawaii

The vines of a Dodder (Cuscuta sandwichiana) plant.

The aggressively parasitic plants belonging to the genus Cuscuta sp. have earned many justifiably derogatory common names, including “Strangleweed”, “Stranglevine”, “Devil Guts”, and “Witches’ Shoelaces”. The more polite Hawaiian name for Cuscuta sandwichiana is Kaunaʻoa.  Swarthmore College biology professor Colin Purrington says, “It’s a horrible existence for the host plant. If plants could scream, they’d have the loudest screams when they had Dodder attached.”

A close-up of the vines, flowers, and foliage of Dodder

DESCRIPTION

A mature Kaunaʻoa plant resembles a tangled pile of yellowish-orange straw wrapped tightly around its host plant. It is mostly stem and lacks normal roots and recognizable leaves. The absence of any green coloration is indicative of the relatively low levels of chlorophyll within the plant’s tissues. The stems of Cuscuta sandwichiana entwine themselves around host plants. Its stems are thin, yellow-to-yellowish green thread-like vines, about 0.8 mm in diameter. Its flowers are white, growing in groups of 3-8 in spreading inflorescences spaced irregularly along the vines. The vines appear to be leafless, but the numerous tiny scales on the surface are in fact reduced scale-like leaves. An individual flower (or “corolla”) is about 2.5 mm long and bell-shaped. The light-brown fruit is a boll containing two to four seeds. The tiny brownish seeds are ovoid, 1.25 to 2.5 mm long, and 1 to 1.5 mm wide.

HABITAT

Cuscuta sandwichiana prefers a tropical or temperate environment with abundant sunlight and rainfall, and soil with good moisture content. It is not frost tolerant, and even a thin dusting of snow will destroy it. Its native habitat is North America, but it has become a widespread invasive species and a noxious weed in many other parts of the world. In Hawai’i, it is considered an introduced invasive species, but some local botanists consider it to be naturalized.

PROPAGATION & GROWTH

The numerous tiny seeds produced by Dodder are easily propagated by wind, water, birds, and humans. They germinate at relatively high soil temperatures (in nine days at about 14°C; in three days at 20-30°C). Seed productivity can exceed 100,000 seeds per plant. Germination occurs at or near the surface of the soil. The new seedling must reach a host plant within 5 to 10 days of germination, otherwise it will die. Some species of Dodder are able to “smell” their next victims. Research has shown that at least one species (Cuscuta pentagona) uses airborne (that is, volatile) chemical cues to locate host plants in its vicinity. Dodder seedlings displayed directional growth responses to volatiles released by species of host plants. When given a choice between volatiles exuded by a preferred host species and those of a non-host plant, the Dodder seedling actually “grew” toward the preferred host by extending its thread-like vine in the right direction. Once the seedling has attached itself to a host, it extends spiral-shaped vines that completely wrap themselves around the stem, branches, and leaves of the host. It then inserts syringe-like appendages (known as hyphae) into the tissue of the host. At this point, the parasitic appendage increases the surface area in contact with cell walls of the host’s tissues by producing haustoria (see photo) that exude enzymes to break down the cell-wall material, enabling the movement of organic nutrients (carbon, etc.) from host to parasite. The original root of the Dodder still anchored in the soil then dies; from then on it obtains all of its nutrients from the host.

Microscopic view of hyphae (long structures) & haustoria (dark spheres). Photo courtesy of E. Boutet.

Throughout its lifecycle, a Dodder continues to grow and attach itself to multiple host plants. In tropical areas (like our Hawaiian rainforests) it lives its life as a perennial vine that grows continuously, reaching high into the forest canopy. In drier temperate regions (such as the leeward shores of individual islands) it exists as an annual plant restricted to relatively low vegetation that can be reached by its offspring seedlings each spring.

HARMFUL EFFECTS OF DODDER

Dodder parasitizes a wide variety of native, weed, and crop plant species. The severity of an infestation depends on the species of the host plant, the climate and time of year of the infestation, and whether there are viruses and other pathogens present in the host. Dodder causes stunted growth or death in its host by disrupting its metabolic processes, literally sucking the nutrients out of it. It also decreases the host plant’s ability to resist diseases; it may spread diseases from one host to another by attaching itself to multiple host plants.

A spreading mat of Dodder (Cuscuta sandwichiana) parasitizes the vines of Beach Morning Glory (Ipomoea pes-caprae) at Kanaha Beach, north Maui.

METHODS OF CONTROL

Physical control of Dodder in agricultural crops is difficult because it requires the destruction of the host plant: this typically involves mowing and burning the cut material where it lies, spraying it with oil or another herbicide, and burning the slash.  Effective control of any kind must begin prior to flowering of this aggressive parasite. When controlling an infestation of Dodder in crop species, it is important to keep seed stock physically isolated from the infesting plants, otherwise the Dodder’s numerous tiny seeds can easily intermix with those of the crop species. This means completely eradicating Dodder infestations from nearby roads and access trails, boundary strips, and adjacent wastelands. Fields that were previously infested by Dodder must be sown with crops or other plant species that are not susceptible. Biological controls have yet to be developed, but agricultural researchers in Russia have described a few species of weevils and fungi that prey on Dodder.

Epiphytic cactus (Euphorbia sp.) ensconced in a tree, Poipu Road, south Kaua'i.

Where I come from in the Desert Southwest of North America, self-respecting Euphorbia don’t behave like this! They stay firmly (and properly) rooted in soil, on the ground. I assumed that some joker had purposely uprooted this “sapling” and replanted it (along with a small handful of soil) in the crevice between the two branches of the tree. I began to notice that several of the other trees had similar Euphorbian “passengers” firmly attached to them. More mature cacti rooted in the ground amongst the trees were, in some cases, growing as tall as their non-cacti grove-mates.

Cacti rooted in soil in grove of trees, Poipu Road, Kaua'i.

“Could it be true?”, I thought: “Are some cacti ‘parasitic’?” Then a long-forgotten bit of terminology from my college biology classes popped into my head: epiphytes! After taking numerous photographs of the spectacular trees and their odd little succulent companions, I returned to Maui and began to fill in the gaps in my knowledge of epiphytic plants with some much-needed research. I soon discovered that I had photographed many different species of epiphytes in the islands without even knowing it.

What is an Epiphyte?

An epiphyte is any plant that grows on another plant; occasionally, epiphytes may also take root on a non-soil substrate, like a building’s rain gutters or a wooden fence post. A true epiphyte uses photosynthesis for energy and derives water and nutrients from the air, rain water, or cloud moisture on the host’s surface. It is believed that more than 15,000 species of epiphytes inhabit the tropical regions of the world; this figure doesn’t account for hundreds of epiphytic species that are, as yet, uncatalogued.

Maile-Scented Fern attached to a tree branch, Nahiku, east Maui.

Some Defining Characteristics of Epiphytes

Some species of epiphytes have developed specialized structures such as cups and scales to collect or hold moisture. However, many of Hawaii’s epiphytes seem to thrive in the numerous cracks, grooves, and pockets of a host plant’s surface (the bark of a tree, for example) where organic debris such as decaying leaves, rotting twigs, and bird droppings readily accumulates, providing an excellent medium to stimulate initial growth. True epiphytes (called “autotrophic epiphytes” or “holoepiphytes”) only employ roots for attaching themselves to a surface, NOT for extracting nutrients. These species never root in soil and remain attached to their hosts for their entire life cycle. They only use their hosts as a means of physical support and do not derive nutrition from them, as do parasitic plant species. However, many species of epiphytes grow so thickly upon the trunks, branches, and leaves of host plants that they restrict their growth to the point that the host plant is severely damaged or dies.

Harts Tongue Fern growing on a tree trunk, Kula, Maui.

Botanists do love their jargon, and so to add a bit of confusion to the meaning of the word “epiphyte”,  more subdivisions were defined. A hemiepiphyte is a plant species that is exclusively epiphytic for one stage of its life cycle, but then becomes rooted in the soil during another stage. A primary hemiepiphyte is epiphytic only during the first half of its life cycle, while a secondary hemiepiphyte assumes an epiphytic lifestyle in the latter half of its life cycle. There’s more of this sort of lumping and splitting of terminology, but I think I’ve muddied the waters sufficiently for now.

Epiphytes exist in habitats where they are subjected to extended periods of environmental stress; these stresses are the driving forces behind their exceptional evolutionary diversification and adaptability. Epiphytes such as many species of orchids live in the upper canopy of the forest where water, minerals, and other nutrients are in short supply.

Orchid growing in the branches of a tree, Kula, Maui.

Epiphytic orchids have evolved specialized structures such as thick stems  to store water and leaf hairs whose function is to close the plant’s stomata when dry conditions set in.  Many species of bromeliads (known as “tank” bromeliads) are able to catch and hold water in their broad, stiff, upturned leaves.

Orchid growing on tree trunk, Poipu, Kaua'i.

Some species of secondary hemiepiphytes have become adapted to the low-light environment of the forest understory. Shaded by gigantic trees of the forest canopy, these species (such as philodendrons) spend their early lives rooted in the soil. As they mature, they grow by sending out long tendrils (internodes) along the  ground, seeking the shade of the trunk of a large tree where the plant continues to grow. This behavior is known as skototropism.

Many epiphyte species occupy microhabitats that dry rapidly. Such an environment promotes strong selection among plant species for resisting drought conditions. One of the most common survival traits developed by epiphytes is Crassulacean Acid Metabolism (CAM), a system of enhanced photosynthesis that enables a substantial increase in the efficient use of water. CAM epiphytes characteristically have thick leaves or succulent green stems.

Epiphyte bromeliads (Tillandsia gardneri) growing on a dead tree trunk, Kula, Maui.

Bird’s Nest ferns (common in Hawaii) form complex tangles of roots and leaves that trap leaf-litter and other dead-and-decaying plant material that accumulates and forms humus. Species displaying this characteristic are called trash-basket epiphytes. The genus Asplenium  sp. is an example of this type of epiphyte common in Hawaii’s rain forests.

Birds-Nest Ferns growing on a Coconut Palm trunk, Keanae Arboretum, east Maui.

Some Advantages of the Epiphyte Lifestyle

Epiphytes have a great many competitive advantages over other rain forest plants.

• The epiphytic lifestyle affords them access to more direct sunlight, a greater number of animal pollinators (birds and flying insects that reside in the forest canopy), and the capability for wider seed dispersal via the wind.
• Epiphytic plants attached to host trees and other plants that reside high in the forest canopy have an advantage over plant species restricted to the ground where there is less light and herbivorous animals (feral pigs, for example) may be more active.
• Epiphytes tend to produce far more seeds than species that root in the soil because large numbers of their seeds fail to reach a suitable substrate in which to germinate. For this reason, many of the seeds of epiphyte species have evolved specialized structures such as wings, glider-like air foils, and parachutes to enhance wind-borne dispersal. Many of the epiphyte species that bear fleshy fruits have developed the ability to crowd thousands of seeds into a single berry.

What About My “Cactus-In-A-Tree”?

It turns out that many species of cacti are able to adopt the epiphyte life style, and it is not unusual to find them growing on trees of tropical rain forests. The spines of tropical epiphytic cacti are much reduced or totally absent, presumably because over-sized spines would prevent sunlight from reaching the photosynthetic stems. Most species of epiphyte cacti have fewer ribs than their desert-dwelling counterparts. Their leaves and stems are more elongated, which enhances light absorption.

Tropical epiphyte cactus (Euphorbia sp.) living happily in the trees on Kaua'i.

So, unlike money, cacti DO grow on trees. Amazing…

A vine-like runner of Koster's Curse (Clidemia hirta), Keanae Peninsula, east Maui.

If ever a plant belonged on the world’s Ten Most Wanted list of Dangerous Criminals, it would most likely be Clidemia hirta, AKA “Koster’s Curse“.  This aggressively invasive pest species is considered to be “armed and dangerous” by range managers and plant scientists throughout the world, and has earned for itself the botanical equivalent of a standing order of “shoot to kill” on all of the Hawaiian Islands.

How it got its Name
The common name for Clidemia hirta is Soapbush. However, it is frequently referred to as “Koster’s Curse” in places where it grows as a noxious weed; this includes Hawaii, where it is sometimes simply referred to as “the curse” for the damage it caused to coconut plantations. Sometime between 1880 and 1886, the hapless Mr. Koster inadvertently introduced Clidemia hirta seeds to coffee nursery seed stocks in Fiji. Since then, it has spread inexorably throughout the islands of the Pacific Basin, including Australia.

The distinctive five-veined leaf of Clidemia Hirta. Note the fine hairs covering the leaves, twigs, and fruits. Nahiku, east Maui.

Description
Clidemia hirta is a coarse perennial shrub that can grow as tall as 5 m under ideal conditions, but its average height is about 2 m. Its branches, vine-like runners, stems, leaves, and fruit are covered with numerous reddish-green bristles (hence its Latin species name “hirta”, which means “hirsute” or “hairy”).

The opposite, roughly ovate leaves are 5-15 cm long, 4-7 cm wide, and covered with fine bristles on both surfaces. The leaf margins are scalloped or toothed, and quite hairy.  Leaf surfaces display five deep veins that originate at the base of the leaf and extend to the apex; numerous smaller lateral veins between give leaves a characteristically pleated or “chessboard” appearance. The upper surfaces are pronouncedly more glossy than the dull under surfaces.

The flowers, fruit, and foliage of Clidemia hirta, Nahiku, east Maui.

The flowers are small (five petals, each about 9 mm across), colored off-white, and form panicles (clusters of flowers) that emerge in the leaf axils or at the ends of branches. Clidemia hirta will set flowers and fruits throughout the year if there is enough moisture in the soil.

When they mature, the fruits are deep-blue to black in color,  hairy, four-celled, and very small (about 8 mm long). The flesh is sweet with a flavor a bit like that of a blueberry, only stronger. A large mature plant will produce as many as 500 fruits a year. Each fruit contains about 100 small seeds (5-6 mm long) that can remain viable in the soil for as long as four years. The fruits are poisonous to goats due to their high concentrations of tannin.

Ripening and immature fruits of Clidemia hirta, Nahiku, east Maui.

Reproduction and Seed Propagation
In rain forest habitats where there is no dry season, vegetative growth and sexual reproduction of Clidemia hirta continue throughout the year.  However, in habitats with seasonal dry periods, the rate and quantity of flowering and fruiting are greatly reduced. Growth is rapid after germination: seedlings may grow into mature fruiting plants within 6 to 10 months.

Seeds most commonly are dispersed by birds, feral pigs (Sus scrofa), mongooses (Herpestes auropunctatus), and humans. Humans are the dominant means of spreading the seeds over long distances. Hunters, hikers, marijuana growers, plantation workers, and their motor vehicles are the main vectors. The bristle-covered fruits are able to cling tenaciously to clothing, equipment, and muddy tires, and so may be transported many miles from the original infestation.

Habitat and Ecology
In Hawaii, Clidemia hirta usually grows in areas that receive more than 127 cm (50 in) of annual rainfall. Its failure to spread to the islands of Kaho’olawe and Ni’ihau may be due to their arid climates and geographic isolation. Although it requires high rainfall and humidity, Clidemia hirta is otherwise able to tolerate a wide range of environmental conditions, which partly accounts for its success as an invasive weed. It prefers forests, plantations, and pasture lands, but it grows equally well in both the full sunlight of exposed ground and the deep shade of a rain forest canopy. It will grow in undisturbed ground, but spreads very rapidly (usually by vegetative growth) in soils that have been recently disturbed by storms, fires, landslides, and feral pigs. Its preferred altitude ranges from a few meters above sea level to more than 1,200 m (about 3940 ft), though it will grow in areas as high as 1,500 m under favorable conditions. When it becomes well established, Clidemia hirta develops dense, monotypic stands that effectively shade out understory plants. In habitats with ideal soil-moisture conditions, mature plants can reach heights in excess of five meters, extending well into the subcanopy of typical Hawaiian forests. However, in more exposed areas mature plants rarely grow more than a meter or two in height.

Geographic Range and Distribution
Clidemia hirta is a native species of the tropical Americas, specifically Central and South America, and the island groups of the Caribbean. It has become a  pest species throughout Oceania, Southeast Asia, and the Indian Subcontinent. Its first documented appearance in Hawaii was on O’ahu in 1941; by 1957 it was officially classified as a “noxious weed” on the island.  Subsequently, it spread to the Big Island (1972), Moloka’i (1973), Maui (1977), Kaua’i (1982), and Lana’i (1988). It is believed that many of the most recent serious infestations of Clidemia hirta on Moloka’i, Maui, and Kaua’i were inadvertently initiated by local marijuana growers.

A mature stand of Koster's Curse doing what it does best: choking off the sunlight to smaller plants of the rain forest's understory.

A Weed with all the “Right Stuff”
The success of Clidemia hirta as an invasive weed in Hawaii is due to a set of unique circumstances, traits, and behaviors, including the following:

• Absence of natural enemies and fast-growing competitors
• Ready availability of several dispersal vectors (birds, mammals, and humans) that aid in seed propagation
• Adapts readily to a wide range of environmental conditions
• Quickly takes advantage of being introduced into to a region with a favorable climate
• Prolific seed production
• Rapid growth and maturation
• Reproduction occurs throughout the year under favorable conditions
• Spreads rapidly into gaps in a habitat opened by fires, storms, and soil disturbance
• Forms dense, impenetrable thickets under forest canopies and shades out understory vegetation beneath them.

Flowers and foliage of the Banana Poka (Passiflora tarminiana), near Waimea Canyon, west Kaua'i.

Passiflora tarminiana is known as “Banana Poka” in the Hawaiian Islands; it is also called Banana Passionfruit and Passionflower. In most of South America (where it originated) it is known as Curuba.  In Hawaii there has been some confusion about the taxonomic designation of this species. It was originally thought to be two distinct species of the genus Passiflora: P. tripartita and P. mollissima. In 2009, the Banana Poka that is found in the Islands was officially given the taxon Passiflora tarminiana; however, many popular books, blogs, and websites about Hawaii’s plant life still use one of the old taxonomic designations.

Description

Under normal conditions, P. tarminiana is a perennial climbing vine that can attain lengths in excess of 20 m and often lives more than 20 years. In the absence of any vertical support, it can assume either a bush-like or trailing habit.

Tri-lobed leaf of the Banana Poka (Passiflora tarminiana).

Leaves are three-lobed and about 15 cm long by 20 cm wide with very serrated margins. The upper surfaces are smooth, dark green, and moderately lustrous, while the under surfaces are light green and covered with fine hairs. The veins are prominent on both surfaces.

Flowers are large (5 to 10 cm in diameter) and are borne singly at irregular intervals along the length of active vines. The 10 petals (3 to 6 cm long) are generally light pink to pinkish white, often displaying a whiter “sport” (or centered stripe). The base of the flower has pale green bracts (modified leaves) enclosing a swollen nectary chamber.  The internal structure of the flower is simple but distinctively colored: it has five stamens with bright yellow anthers, and three pistils with light green stigmas.

The distinctive flower of the Banana Poka (Passiflora tarminiana).

Fruit and Seeds – The fruit is an elongated berry (8-15 cm long and about 4 cm in diameter ) that resembles a banana’s fruit. Light green when immature, it ripens to a yellowish-orange color, at which point it is edible. The berry contains approximately 180 seeds, each embedded in an edible aril (a sweet, fleshy capsule enclosing the seed, as with a pomegranate seed). The seeds are small (about 5 mm in diameter), asymmetrical, and dark reddish-brown when dry.

Fruit of the Banana Poka (Passiflora tarminiana).

Reproduction and Propagation

Pollination – After one year’s growth, the Banana Poka produces its large and conspicuous flowers throughout the year, so there are many opportunities for spontaneous self-pollination and cross-pollination (or “outcrossing”) by the numerous flying insect species that inhabit the Islands (mostly bees and syrphid flies). A newly opened flower displays its many prominent exposed stamens that increase its chances of being cross-pollinated by flying insects. In flowers where cross-pollination does not occur, each one can pollinate itself by moving its stigmas to touch the stamens.

A ripening curuba (fruit) of a Banana Poka, sliced in half to show the edible arils (seed coat).

Dispersal – The fruits ripen in about three months and are produced throughout the year in Hawaii. The fruit (and, consequently, its numerous seeds) is widely dispersed locally by birds, as well as domestic and feral mammals, particularly feral pigs (Sus scrofa). Fruit- and seed-eating birds, as well as humans, also spread the seeds over longer distances. Seeds can remain dormant yet viable for more than 60 weeks when buried under as little as 10 cm of topsoil. Banana Poka is also very capable of vegetative reproduction, where the interconnected portions of a mature plant decay or are otherwise separated from the parent plant and take root on their own.

Seeds of the Banana Poka (Passiflora tarminiana).

Range and Distribution

P. tarminiana is a native of the tropical regions (specifically Bolivia, Venezuela, and Colombia) of the Andes Mountains of South America. Populations of this species are sparse (two or three plants per hectare) in this part of the world and its fruit and flowers are aggressively consumed by many species of herbivorous insects, thus preventing it from becoming a pernicious weed as it has in Hawaii. Here it inhabits mesic forests of Koa (Acacia koa), ‘Ohia (Metrosideros polymorpha), Black Wattle (Acacia mearnsii), and other native species of trees. It’s altitude range extends from 850 to more than 2,200 m. Recently Banana Poka has been invading subalpine shrublands on Maui, as well as agricultural and residential areas.

Environmental Tolerances and Preferences

Banana Poka can tolerate a wide range of climate variation. It is relatively frost-tolerant and will grow in both full shade and full sunlight, but seedlings tend to be less tolerant of full shade, and optimal growth only occurs in full sunlight. P. tarminiana prefers a seasonal climate where annual mean temperature is 13°C and mean annual rainfall is about 130 cm.

Introduction History

Banana Poka was first introduced to the island of Hawai’i in about 1920, and shortly thereafter to the other neighbor islands. By 1926, botanists were finding naturalized specimens in the wild on the Big Island, as well as on Maui and Kaua’i, which attests to its ability to spread quickly in a favorable climate. Currently, P. tarminiana occupies large areas of Kaua’i and Hawai’i, in some places forming a continuous cover.

A pair of vines of the Banana Poka (Passiflora tarminiana). These were part of a plant that extended from the tops of some Koa trees to where I was standing, more than 30 feet below!

Ecological Impacts

The Banana Poka’s very effective methods of reproduction, propagation, and competition are directly responsible for its successful colonization of the Hawaiian Islands and its well-deserved epithet as a serious pest species outside its native range.

• The tendency of P. tarminiana to rapidly increase its growth rate as the intensity of sunlight increases enables it to invade openings in an established forest canopy caused by storms, logging, and feral pig damage. It also forms dense colonies along forest margins where the shade of the canopy is sparsest.
• Once the active vines of the Banana Poka reach the uppermost heights of a forest’s canopy, they rapidly spread out laterally, smothering or shading-out less aggressive native species of trees and shrubs.
• Disturbance of topsoil by the rooting activities of feral pigs increases the rate of invasion of this species. The increasing numbers of feral pigs on all of the Hawaiian Islands has contributed immensely to P. tarminiana’s invasion of native forests, scrublands, pastures, forestry plantations, and even relatively barren lava flows. Wherever pig damage is the worst you’ll find large patches of Banana Poka.
• There are almost no species of herbivorous insects that naturally prey on P. tarminiana in Hawaii, and so it is able to set more flowers and fruits, which results in greater plant densities than in its native range.
• P. tarminiana’s ability to employ either cross-fertilization or self-fertilization, coupled with its adaptations that enable long-distance dispersal of its seeds, allow it to invade isolated areas far from the center of its main infestation.
• In addition to all of the other negative ecological impacts of the Banana Poka, a very dense population of this species can literally smother even the tallest native trees in a shroud of vines. Native species can be shaded out; prevented from regenerating damaged limbs, trunks, and roots; and can even be toppled by the sheer weight of the dense curtain of vines. Where forest canopies have been opened in this or other ways, dense mats of Banana Poka vines soon drape themselves over the understory trees and shrubs. In the long term, this competitive activity alters the composition and physical structure of a forest, which adversely affects already endangered species of native birds and other animals.

Control and Management

Attempts at eradication and controlling the spread of this aggressively invasive species have, for the most part, failed completely; use of modern methods of biological control have been shown to be totally ineffective. The very labor-intensive application of physical and (to a lesser extent) chemical control methods have been more successful when employed along the leading edge of infestations to prevent the infestation from advancing further.

Chemical Control – On a large scale, application of chemical control agents such as herbicides is impractical because the current infestation of Banana Poka is spread over large, often inaccessible areas and the main biomass of the infestation overlies many non-target plant species. However, frequently repeated physical applications of contact herbicides (such as Roundup) over small areas, particularly at the leading edges of an infestation, have been successful at controlling its spread.

Physical Control – A few purely mechanical means of controlling Banana Poka have been successful in small selected areas; these include manually pulling the entire plant out of the ground by its roots. Don’t laugh: a lot of property owners swear by this method and so far it seems to be the only effective means of controlling this monster. Natural areas and other valuable parcels of land not yet infested can be fenced-off to prevent feral pigs from spreading the seeds and disturbing topsoil.

Biological Control has not been very successful in controlling the spread of P. tarminiana. Species of mold and fungi have been introduced throughout the infested areas on Maui, but the species known to prey on Banana Poka elsewhere in the world have had a great deal of difficulty establishing themselves in our climate. Introduced predatory species often fail to survive the dry season, perishing before they can become naturalized. The same fate has befallen herbivorous insect species known to consume the flowers and foliage of P. tarminiana.

Typical stand of mature Koa Trees (Acacia koa).

So I did what any scientist does when confronted with his own ignorance: I cheated. I visited a place where trees already come with convenient labels attached: a botanical garden. It didn’t help. Out in the field, I kept running into trees that looked like the big fellow in the tree museum, but they had the wrong leaves! They looked more like those you’d find on a eucalyptus tree: long, narrow, and slightly curved like a Marine Corps dress sword.

A newly mature Koa Tree.

One day I got a real surprise: I found an entire stand of these trees that had TWO KINDS OF LEAVES! I went home and consulted the ultimate source of questionable but plentiful knowledge, Wikipedia. Sure enough, said the Great Wiki, at one point in their deceitful lives, Koa Trees actually DO have two kinds of what appear to be “leaves” on the same tree! All that time I’d spent crashing around in the bush looking for them, I had probably seen hundreds of Koa trees and didn’t even know it. That seemed unfair, somehow.

The phyllode (left) and true leaf of an immature Koa Tree.

Description

A large evergreen hardwood tree, Koa trees can reach heights of 15 to 35 m (50-115 ft); their branches create a canopy spread tens of meters wide. It is also one of the fastest growing native trees: young trees can reach 10 m in height in the first five years.  However, there is a lot of variation in size and growth habit from one population to another. Its form can range from that of a large upright trunk to several low, sprawling shrub-like trunks. In the Hawaiian language, “koa” means brave, fearless, bold, or warrior.

Phyllodes and bipinnately-compound true leaves of an immature Koa Tree.

Leaves – Aside from its great stature, the distinctive silver-green foliage is the most notable of the Koa tree’s physical attributes. Immature seedlings display bipinnately compound true leaves with 12–24 pairs of leaflets, like other members of the Fabaceae (legumes) family. At about nine months of age, it begins to produce large (7-25 cm long and 0.5–2.5 cm wide), flat, vertically elongated sickle-shaped non-compound “leaves”. These are phyllodes, blade-like leaf-stalks that develop as an expansion of the leaf petiole. For a time, a maturing tree bears both the true leaves and these leaf-like phyllodes. Eventually, all of the true leaves are replaced by the phyllodes on the fully mature tree. The vertically flattened orientation of the phyllodes allows direct sunlight to pass easily to lower levels of the tree.

Close-up of a true leaf (left) and a phyllode from an immature Koa Tree.

True leaves promote more rapid early growth when moisture is adequate; however, during periods of drought, phyllodes are better adapted to promote growth. Phyllodes transpire about 20 percent more moisture than true leaves during times of moisture stress, and their stomata (moisture-transpiring pores on the surface) close four times faster after dark, preventing moisture loss. While fully mature trees usually bear only phyllodes, sometimes true leaves appear on the trunk or lower branches of the tree, particularly after a tree sustains wounding or other traumatic damage.

Cross-section of the trunk of a Koa sapling showing wood's grain and color.

Outer Bark – The outer bark of young trees is smooth in texture and may be covered with harmless growths of bright orange-red lichen. At 8 to 10 years of age, the bark develops a rough, fissured texture. At this point in the life cycle, its color is light to dark brown, often highlighted by numerous growths of silvery to light-green lichens.

Flowers and foliage of a mature Koa Tree.

Flowers – Flowers are usually borne over the outer part of the tree’s crown, at the tips of branches. The pale-yellow axillary racemes with spherical heads (8-10 mm in diameter) are nearly identical to those of the Koa Haole (Leucaena leucocephala). Starting at about 2-3 years of age, flowers are produced throughout the year or seasonally, depending on the location.

Fruit – Fruit production begins at about five years of age and continues for another 20 to 25 years. The fruit is a pod (7-15 cm long and 1.5-2.5 cm wide) containing 12 dark-brown to black flattened ellipsoidal seeds (5-10 mm in diameter). Each seed is protected by a very tough seed coat that enables an ungerminated seed to remain dormant yet viable for as long as 25 years. The seed coat must be thoroughly abraded (scarification) before the seed will germinate successfully.

Close-up of the fruit (seed pods) of a Koa Tree.

Genetic Variation – Although native to the Hawaiian Islands, Koa is a highly variable species in its general appearance, the nature of its wood, and its environmental tolerances. Trees found on Hawai’i Island tend to be taller and more robust with broader phyllodes, while trees of the other islands have shorter trunks and more curved phyllodes. These and other distinctive physical attributes appear to be readily inherited by subsequent generations of trees within a specific local population, as well as within island-wide populations.

Reproduction, Growth, and Regeneration

Pollination – One of the pollinating insects known to visit Koa flowers is the Honeybee (Apis mellifera). Other insects, birds, and wind may also enable the pollination of Koa trees, but the mechanisms for this process are not well documented for this tree species.

Close-up of the flower (raceme) of a mature Koa Tree.

Seed Propagation – Koa seeds are usually not dispersed very far beyond the crown of the parent tree but seeds can be carried long distances by strong winds and torrential rains. In order for Koa seeds to germinate, the tough walls of the seed pod must first be thoroughly abraded (known as “scarification”). The mode of germination is epigeal: that is, the seed expands, throws off the seed coat, and begins photosynthesis above the ground. Under favorable conditions (bare mineral-rich soil, adequate moisture, and nominal exposure to sunlight), Koa seedlings will grow readily and rapidly. Soil aeration and temperature also may influence the rate and volume of germination.

Natural Regeneration – Koa is both a rapidly growing, light-demanding pioneer tree that quickly colonizes open sites, and a long-lived tree that is part of mature forests. Koa naturally regenerates from buried “seed banks”, large numbers of seeds that have been buried in the soil for years or even decades. These germinate when the soil is exposed to sunlight and warmth by natural means, such as fire or wind-throw of large individual trees. Naturally regenerated stands of pure Koa may have as many as 20,000 seedlings per hectare. These grow quickly and the maturing trees may close canopy and form a solid stand in less than 10 years. Growth of individual trees slows thereafter as the trees compete for growing space.

“Suckering” – Koa trees also employ vegetative reproduction by producing numerous root suckers. This method of regeneration is often evident in overgrazed stands of trees. Once a pasture formerly occupied by Koa trees is withdrawn from grazing, healthy seedlings quickly develop, often tens of feet from the bases of dead or severely damaged trees (in some cases, more than 30 m away).

Koa trees adapt well to adverse environmental conditions. Stands of trees subjected to fire damage and logging usually recover quickly, sending up new seedlings within months. This is due to the ability of the seeds to germinate in almost any seedbed, from bare ground to the stumps and fallen branches of trees and other plants, as long as moisture is available in adequate quantities.  However, like other trees native to the Hawaiian Islands, they do not fare well where feral pigs and goats, or range cattle overgraze. But once an area previously occupied by a stand of Koa trees is withdrawn as pasture land or otherwise protected from the predations of feral pigs, seedlings soon reappear. Koa seedlings do not grow well under the denser canopy of the rain forest unless openings in it have been created. Serious disturbances of the rain forest canopy, such as fires or hurricane-induced wind throw, commonly stimulate large-scale colonization by Koa seedlings.

Phyllodes and true leaves growing on the same twigs of an immature Koa Tree.

Distribution and Habitat

The Koa Tree is native to the mesic and wet forests of the islands of Hawai’i, Maui, Lana’i, Moloka’i, O’ahu, and Kaua’i. It grows in nearly pure stands or in mixed stands dominated by ‘Ohi’a lehua (Metrosideros polymorpha). While a wide variety of smaller native understory trees and plants are found in Koa forests, the actual amount of growth and ground coverage of these species is sparse.

Koa trees prefer flatlands and hillsides at altitudes of 100 and 2,300 m where annual rainfall is between 85 and 500 cm (33-200 in). They also grow in areas with much less than this amount of rainfall, but growth is considerably slower and the overall health of the tree may be adversely affected. This species’ nitrogen-fixing abilities allow it to grow in a wide variety of volcanic soils, regardless of the geologic age or geochemistry of the parent rocks. It grows best in soils that are acidic to neutral (pH = 4 – 7.4), principally Inceptisols derived from volcanic ash deposits and Histosols with good drainage.

The foliage (all phyllodes) of a mature Koa Tree.

Environmental Tolerances – Although this species prefers an environment with moderately high amounts of annual rainfall, it is also somewhat drought-tolerant, being able to survive under drought conditions for as long as five months. It prefers full sunlight throughout its lifecycle and is intolerant of shade. Root suckers will not produce healthy seedlings in areas covered by tall grass or impenetrable undergrowth. As mentioned above, Koa root suckers will re-sprout above ground after a fire, but the trunk, branches, and foliage are not fire resistant and are very susceptible to fire damage. Mature trees are resistant to frost damage, but young seedlings are easily killed off after a single hard freeze.

Reactions to Competition – Competition among individual Koa trees in a dense stand severely limits the growth and development of older saplings. In very densely populated stands, many trees are not growing at all, although a few individuals may emerge out of the shade of the forest canopy and so overtop their companions. The Koa’s ability to shed its lower branches completely when subjected to crowded conditions is a useful adaptation.

Mature, healthy native Hawaiian forests contain a very diverse mixture of tree species that may include only a few Koa trees per hectare. The reason for this is that individual Koa trees do not propagate in great numbers in the full shade of a forest; quite simply, under normal conditions, it is not able to grow up through the canopy of other trees. Once a Koa is overtopped by another tree, even one of its own species, it ceases to grow any taller. The Koa tree must depend on large tree-fall gaps in order to propagate in large numbers and colonize a normal forest. Stands of Koa saplings are often seen growing amongst large tree stumps of old-growth trees felled by logging or storms.

Potential for Invasiveness – Although it is not commonly planted outside its native range, the Koa is a fast-growing nitrogen-fixing tree species, so its potential for invasiveness may be high outside Hawaii. However, this species’ intolerance to shade, hard freezes, drought, and fire would not allow it to survive in a temperate climate.

Diseases and Pests

The Koa tree is susceptible to numerous fungal diseases, particularly several species of the vascular fungus Fusarium sp., a disease-causing fungus found throughout the world. Koa Wilt is a serious, often fatal disease caused by Fusarium oxysporum, a soil-borne fungus that is common in Hawaiian soils. Ambrosia beetles (such as Xyloborus sp.) transmit the fungus Fusarium solani, which causes wood staining and mainly affects seedlings. In both cases, the fungus enters through the trees’ roots and migrates upward through stems and branches, where it blocks vascular tissue and chokes off the water supply to the leaves. The leaves then wilt and turn brown.

Twig borer insects damage the branches of a Koa tree and may kill young seedlings. Livestock (particularly goats and beef cattle), as well as feral pigs, readily consume small seedlings and uproot maturing trees. and can also damage young trees by eating the leaves, stripping the bark, and trampling the extensive surface root systems. Seed predators include seed weevils (such as Araecerus levipennis) and the Koa Seedworm moth (Scotorythra paludicola) cause defoliation that can kill trees outright. When grown in grassy areas at elevations lower that its normal altitude range, the Koa is susceptible to parasitic infestation by Root-Knot Nematodes (usually of the genus Meloidogyne sp.). They exist in the soils of regions with hot climates or short winters. The larval form of the worm infects plant roots, causing the development of root-knot galls that drain the plant of nutrients. An infestation can kill a sapling outright; mature trees usually survive infestation, but are seriously debilitated and underdeveloped.

Banana Poka (Passiflora tarminiana), an aggressively invasive species of climbing vine, has overgrown and suppressed stands of Koa, particularly on the Big Island and Kaua‘i. Tropical ash (Fraxinus uhdei) occupies the same environment as the Koa and often shades out its saplings. Strawberry Guava (Psidium cattleianum), considered a noxious weed in the Hawaiian Islands, completely occupies the under story of many forests and prevents propagation and regeneration in Koa-dominated stands of trees.

Ecological Importance

Habitat Quality and Remediation – The Koa tree is a nitrogen-fixing leguminous species; for this reason, it is thought to contribute significantly to the nitrogen content of otherwise nitrogen-poor volcanic forest soils. The Koa is one of the few native Hawaiian plant species that is able to germinate in grassland and therefore can be instrumental in restoring native forest habitat. Disk harrowing the soil of former pastureland scarifies Koa seed pods already present in the soil and encourages large numbers of Koa to germinate. Koa trees reduce radiative cooling of the ground surface, preventing frost damage to its own seedlings and those of other species of native trees, such as the O’hia (Metrosideros polymorpha).

Wildlife Habitat – The Koa tree is a native Hawaiian species of critical ecological importance because it provides a suitable habitat for many native species of birds, insects, and other plants. Koa flowers provide pollen and nectar for bees. Large old trees provide important nest sites for birds. The endangered ‘Akiapola’au (Hemignathus munroi), a species of finch in the Hawaiian Honeycreeper family endemic to the Koa-dominated mesic and wet forests of the Island of Hawai’i, eats insects found only in the bark and rotting wood of Koa trees. Koa forests are also the home of the endangered ‘Akepa (Loxops coccinea) and the Hawai‘i Creeper (Oreomystis mana).

Traditional and Modern Commercial Uses

Koa is an important timber tree in Hawaii. The rich, dark colors and intricately-patterned grain of its wood is much sought after as a decorative veneer in Island homes; it is processed in California from wood shipped from Hawaii. I recently bought a solid-core wooden door with Koa veneer on both sides. When I applied a coat of clear acrylic preservative to the exterior of the door, a beautiful reddish-brown curly grain leapt out of the wood!

Koa-wood veneer applied to the body of an acoustic guitar. Note the intricate patterns of the tight grain of the wood. (photo courtesy of The 12th Fret

Ancient Hawaiians used Koa wood for canoe paddles, spears, surf boards, and decorative bowls. Today, Koa wood is the preferred medium of a flourishing crafts industry in Hawaii.

Canoe Craft – Traditionally, a single trunk of a Koa tree was used for the hull of a canoe (wa‘a), from one-person fishing canoes to the huge ocean-going voyaging. Today, canoe carving is a living tradition in Hawaii, and Koa-wood canoes are still made for and used in races.

A fair amount of milling is required during the production of Koa-wood lumber, veneer, molding, and flooring. The high value of the wood favors small-scale milling in the field with a portable mill; however, this production method typically yields smaller amounts of usable wood than do large, fixed mills.

Koa-wood furniture is the main product of Hawaii’s $30 million-a-year forest industry. In the past, harvesting large quantities for export led to rapid boom-and-bust cycles, and depleted resources of Koa trees. Alternatively, a gradual, well-planned sustained harvest of Koa trees should ensure that Hawaii’s local furniture and craft industry remains viable well into the future.

Unfortunately, this admirable species has fallen victim to the confusion and contention of the botanical world’s “Taxonomy Wars”. As a result,   Beach Naupaka may be assigned  either of two competing scientific names, depending on the biased opinion of a particular author or researcher. But let’s save my “rant” on the subject of the taxonomic confusion surrounding this species for the end of this blog entry. First things first: Who, What, and Where is the Beach Naupaka?

Beach Naupaka or Naupaka Kahakai (Scaevola sericea) foliage and flowers, southeastern coast of Lana'i.

General Description
Beach Naupaka is native or endemic to most of the Pacific islands, including the Hawaiian Islands, occurring along beaches throughout the Pacific basin. It is a tall bush-like perennial shrub that commonly forms dense hemispherical mounds of light-green foliage, its branches taking root where they touch the ground. Although individual stands can grow to more than five meters in height, most are considerably wider than they are tall. The simple, smooth-margined leaves are 8-14 cm long, are broader at the tip than the base of the leaf, and their edges often curl back under themselves. They typically are crowded together at the tips of growing trigs. Beach Naupaka is sometimes called the “half-flower” because the flower heads have petals on just one side, making them appear to have been torn in half. The five petals are white or cream-colored, often with purple streaks. The flowers grow in small clusters from between the leaves at the stem tips and have a distinctively pleasant fragrance. The fruit is a fleshy spherical “drupe” 1.5-2 cm  in diameter with sepal lobes persistent at the tip. The drupe turns from green to white when mature. Each fruit contains 2-4 seeds in a hard woody “stone” surrounded with corky tissue that allows the fruit to float in water.

Naupaka, Hala Trees, and Coconut Palms festoon the rocky shoreline of Pailoa Bay, Waianapanapa State Park, east Maui.

Habitat
Beach Naupaka is common in the hot, dry coastal areas of most of the Hawaiian Islands, with the exception of the smaller islets at the extreme northwestern end of the island chain. It grows naturally on sandy beaches, forming dense thickets on seaside cliffs and sand dunes. This adaptable species is also common on hillsides and lower mountain slopes, pasture lands, roadsides, and encroaching urban areas. It is able to survive in beach-front environments where the spray from breaking waves deposits large quantities of sodium salt on its leaf surfaces and high concentrations of sodium salt in its water source. It prefers sandy, well-drained soils. It is very drought tolerant and can withstand annual average air temperatures as low as -1 degree C; of course, temperatures in the plant’s natural habitat rarely are that low.

The fruit (or "drupes") of Beach Naupaka, Papaula Beach, north Maui.

Propagation and Invasive Qualities
Beach Naupaka is very adaptable and propagates quickly. In the state of Florida, it is considered an aggressively invasive weed, out-competing vulnerable native plant species. Its presence there was first reported in 1976, possibly introduced from Hawaii. This species’ most common method of propagation is from seed. The corky interior of the fruit allows it to float readily in water. The seeds are able to remain viable in salt water for more than a year, but they will only germinate in the presence of fresh water, as when washed up on a beach routinely subjected to moderate-to-heavy rainfall.

My rant: What’s In A Name?
Taxonomy is a field of study within the biological sciences that is devoted to the identification, naming, and classification of living things according to apparent common characteristics. It is also a field of study that attracts some of the world’s biggest egos and most anal-retentive personalities. The binomial system used to name individual species of plants and animals, while seemingly straight forward at first glance, can be so Byzantine in complexity that it perpetuates centuries-long struggles to give Latin names to simple creatures like Naupaka. To get an impression of just how complex the taxonomic naming process can be, go to the BIOLOGICAL CLASSIFICATION web page on Wikipedia (http://en.wikipedia.org/wiki/Biological_classification) and attempt to read through the section on Modern Systems of classification.

Fruit of Beach Naupaka (Scaevola sericea), Kanaha Beach, north Maui. Note the prominent sepal nodes on the tips of the mature drupes.

The following is an excerpt from the International Code of Botanical Nomenclature (ICBN) (Saint Louis Code, Electronic version), THE authoritative codex supposedly recognized by all the combatants in the field of taxonomy. This section of the code lays out how to publish a species’ name correctly. Note that this excerpt uses our own Naupaka as an example.

CHAPTER IV. EFFECTIVE AND VALID PUBLICATION
SECTION 2. CONDITIONS AND DATES OF VALID PUBLICATION OF NAMES
Article 33
33.2. If, for a presumed new combination, no reference to a basionym is given but the epithet of a previously and validly published name that applies to the same taxon is adopted, the new combination is validly published as such if, and only if, it would otherwise be validly published as the name of a new taxon (see also Art. 33.6(d)).
Ex. 3. Scaevola taccada was validly published by Roxburgh (1814) by reference to an illustration in Rheede (Hort. Malab. 4: t. 59. 1683) that appears to be its sole basis. As the name applies to the species previously described as Lobelia taccada Gaertn. (1788), it is treated as a new combination, S. taccada (Gaertn.) Roxb., not as the name of a new species, even though Gaertner is not referred to in Roxburgh’s protologue.

The following is the United States Department of Agriculture’s official plant profile for Naupaka.

USDA NRCS PLANT PROFILE
Scaevola sericea Vahl var. taccada (Gaertn.) Thieret & B. Lipscomb
Genus  Scaevola – naupaka
Species  Scaevola sericea Vahl – beach naupaka
Variety  Scaevola sericea Vahl var. taccada (Gaertn.) Thieret & B. Lipscomb – beach naupaka
Alternative Botanical Names
Scaevola taccada (most commonly used – incorrectly!!!)
Lobelia taccada
Scaevola fauriei
Scaevola frutescens
Scaevola koenigii
Scaevola plumerioides

Beach Naupaka (Scaevola sericea) colonizing the sand berm along a stretch of Kanaha Beach, north Maui.

So… did you notice that the USDA’s plant profile and the ICBN do not agree on the correct name for poor old Naupaka? If these two august and widely respected authorities cannot agree on a taxonomic designation, how can you expect anyone else to do so? This plant was first officially identified in 1683, but after almost 330 years, researchers, educators, and hobbyists still can’t agree on the scientific name!

Blame it on the Web?
Quite apart from the dueling egos in the academic world, controversies over taxonomic names is perpetuated by the prevalence of “Monkey-See-Monkey-Do” naming practices on the Web, and the ignorance, stupidity, and outright carelessness of webmasters who want to make it look like they actually researched the taxonomic issue but really didn’t. It’s a simple matter to trace the original source of a problematic species name back through all of the copycat websites by looking for repeated spelling errors and persistently incorrect genus/species attributions common to the original perpetrator and all his imitators. A little more diligent research on the part of the webmasters of botanical websites would go a long way to alleviating this problem, but “due diligence” is not practiced extensively on the Worldwide Web.

Fruit and foliage of 'Ohelo (Vaccinium reticulatum), Hosmer Grove, Maui.

Distribution and Habitat

‘Ohelo is native to the Hawaiian Islands where it grows in subalpine and alpine shrublands at elevations from 2,000 to 12,000 feet (610 – 3,600 m). It is most numerous on the main islands of Maui and Hawai’i, and to a lesser extent on Kaua’i, O’ahu, and Moloka’i. It is well adapted to growing on fresh lava flows, beds of volcanic ash, and cinders; it is among the first plants to colonize these inhospitable substrates. It has a high tolerance for volcanic activity and is known to survive ash falls deeper than 25 cm.

Description

Vaccinium reticulatum is a small (10-130 cm tall, rarely as tall as 2 m) flowering shrub in the Cranberry family (Ericaceae). It closely resembles several species of North American blueberries. Its Hawaiian name, ‘Ohelo, is also in common use throughout the scientific community. This species displays a lot of variation in its physical characteristics (such as leaf shape, and color and shape of flowers and fruit) to such an extent that local populations and even individual plants have been accidentally categorized as different species. The stiff, upright branches grow from underground stems (rhizomes) that develop when the plant reaches full maturity (at about 3 years).

Flowers and foliage of Vaccinium reticulatum, Haleakala National Park, Maui.

Leaves – The oval-shaped evergreen leaves are about 1.5 to 3 cm long. They are spirally arranged on the twig. When newly emerged they are red, then turn bluish-green or pale green with reddish patches as they mature. The shiny, leathery upper surfaces of the leaves may be smooth or somewhat hairy (pubescent). The leaf margins may be smooth or toothed; occasionally the edges are curled under. This wide variation is partly due to the fact that ‘Ohelo has both juvenile and adult foliage growing on the plant at the same time. It is not unusual for the uppermost leaves of the main stem to have adult foliage while the rest of the plant displays juvenile foliage.

Flowers – The numerous and attractive flowers are bell-shaped, 8-12 mm long, vary in color from red to yellow or pink, and have 5 petals and 10 stamens. The single flowers grow out of the bases of the leaves. Flowering occurs throughout the year. It takes about five years for plants grown from seeds to set flowers. Unlike most of the other species of the genus Vaccinium, the flowers of V.  reticulatum are self fertile. However, self pollination results in the production of fewer seeds per berry than are produced by flowers that are cross pollinated. The nectar produced by the flower is an important food source of endangered Hawaiian native bird species such as the Scarlet Hawaiian Honey Creeper (Vestiaria coccinea) or ‘i’iwi.

Mature 'Ohelo berries, Hosmer Grove, Maui.

Fruit – The edible blueberry-like fruit is 8-12 mm in diameter and is generally bright red in color but may also be yellowish-green, purple, orange, pink, or even dark bluish-black. The color does not necessarily indicate the ripeness of the berry. The peak of berry production is June to September, when the fruit is harvested on Maui and Hawai’i for jams, jellies, and other preserves. ‘Ohelo was one of the few plants native to Hawaii with palatable fruit, and so early Hawaiians emphasized this distinction by referring to this species as ‘ohelo ‘ai (“edible ohelo”).

Seeds — Each berry contains approximately 70 to 200 tiny brown seeds, of which at least half are not viable. The seeds are round, triangular, or elliptical in shape. They take 50 to 60 days to ripen. The berries are the preferred food of the indigenous Hawaiian goose, the Nene. The birds consume large quantities of berries, broadcasting the seeds over large areas in their droppings.

Traditional Uses and Practices

The early Hawaiians believed that the `ohelo was sacred to Pele, the goddess of fire, lightning, dance, volcanoes, and violence. Ritual offerings to Pele included ‘ohelo branches with the berries still attached; these were thrown into the fire pit called Halema’uma’u, the crater at the summit caldera of Kilauea, Hawaii’s most active volcano. When eating the berries, it was customary to offer Pele the first one by throwing it in the general direction of Kilauea, thus appeasing her. The myth of the deification of one of Pele’s many sisters tells how the ‘ohelo became sacred to the goddess. Ka’ōhelo was a mortal sister of Pele. Just before her death, she instructed her son Kiha to bury her “on the navel of your grandmother at Kilauea” on Hawai’i. When she died, her bones and flesh were scattered to the other main islands where they became ‘ohelo bushes. The best known association of Pele with ‘ohelo berries is Proverb 2044 of Mary Pukui’s “Olelo No ‘Eau”: “Mai hahaki ‘oe I ka ‘ohelo o punia i ka ua noe.” (“Do not pluck the ‘ohelo berries lest we be surrounded by rain and fog.” Early Hawaiians treated abdominal pains with ‘ohelo leaf buds, leaves and fruit, combined with coconut meat, sugar cane, and the various parts of other medicinal plants. The ingredients were then pounded into a mash, strained through the leaves of ‘ahu’awa (Cyperus javanicus, a native sedge), and drunk in the morning and evening. The flowers and fruit were (and are to this day) used in lei making.

Closeup of leaves of V. reticulatum showing how flower grows out of the base of the leaf stem.

Commercial/Agricultural Uses

Currently, V. reticulatum is being researched for the feasibility of production of the species as an ornamental potted plant in Hawaii and Oregon, and as a specialty berry crop in Hawaii. As I mentioned earlier in this post, the ripe berries of the ‘Ohelo are extensively harvested by local residents to make preserves and pie filling. They scour the countryside in large numbers during picking season, disrupting fragile subalpine and alpine ecosystems and habitats. This impact on the environment could be minimized if the berries could be commercially grown and market to meet the demand for the fruit.

Red Leaf Disease

Red Leaf Disease, which is caused by the infective presence of the fungus Exobasidium vaccinii, affects all of the native species of Vaccinium sp. in Hawaii. While this disease is conspicuous and widespread in the Hawaiian Islands, its disfiguring symptoms are easily mistaken for normal foliage growth in otherwise healthy-looking plants.  When I first photographed the plants included in this blog post, I was attracted to them by the bright-red clumps of foliage on more mature plants, thinking this was their normal coloration.

Foliage of V. reticulatum showing "Witch's Broom" symptom of Red Leaf Disease.

Viewable symptoms include the presence of clusters of conspicuous blood-red clusters of leaves high on the plant, the formation of contorted and scraggly-looking “witches’ brooms” on the tips of infected branches, and swollen branches that eventually become defoliated and die. While juvenile foliage of the ‘Ohelo often has a reddish coloration when it first appears, the leaves of branches infected with the fungal spores are noticeably curled at the margins by comparison with healthy leaves. In an ongoing attempt to learn how to control the spread of Red Leaf Disease in natural populations, U.S. National Park Service scientists have been experimenting with courses of various antibiotic drugs administered to infected ‘Ohelo plants in the Volcanoes and Haleakala National Parks on Hawai’i and Maui, respectively.

A typical blossom of Hibiscus tiliaceus, Lawai, Kaua'i.

DESCRIPTION

Hibiscus tiliaceus is known by many common names throughout its range, including Beach Hibiscus and Sea Hibiscus. It is called Hau in Hawaiian. This is a highly variable species in the taxonomic sense: it includes several subspecies that are worthy of being classified as distinct species in their own right. There is also a considerable degree of morphological variation as well, particularly in flower coloration and leaf morphology; this is probably due to environmental factors, since it is such an adaptable species. H. tiliaceus is an evergreen tree that can grow to heights exceeding 10 m with a trunk as much as 15 cm in diameter. Usually the canopy of a mature tree is much wider than the height of the tree. It has a short trunk with many crooked and intertwined branches that form an impenetrable thicket; however, it may also have a shrub-like form with prostrate, ground-hugging branches. The outer bark is gray to light brown and is smooth to slightly fissured when the tree is young, becoming thicker and rougher with age. The large (8-20 cm long, 6-15 cm wide), simple heart-shaped leaves are bright green on the upper surface and grayish-green and hairy on the under surface. The flowers are bright yellow with a dark red center when they first open. Individual flowers are roughly cup-shaped with a corolla consisting of five radiating oblong petals 4-6 cm long. They are typical of the genus Hibiscus sp.: brightly colored, fragile, and short-lived (typically just one day). During the course of the day, the color of the petals deepens to a dark orange and finally pinkish-red when the flower drops off. The tree produces new leaves, flowers, and seeds all year long.

The flower and foliage of Hibiscus tiliaceus.

PROPAGATION & GROWTH

Seeds are borne in light-brown  ovoid capsules (2 cm long) that take about seven weeks to ripen and then split open into five segments, each one containing  15 to 25 dark-brown hairy seeds (3-5 mm) that germinate in 2-4 weeks. The seeds remain viable after floating in seawater for several months, which probably accounts for this species’ wide distribution. H. tilaceus also propagates  by aggressive vegetative growth from broken twigs and branches, as well as producing numerous “suckers” from its shallow lateral root system. The long  side branches can take root where they touch the ground. Plants that are produced from vegetative propagation can set flowers in less than one year, while seedlings require 2-3 years before they are mature enough to produce flowers. This species is well known for its rapid and aggressive branching and spreading habit. Its growth rate is quite fast, producing as much as 1.5 m of new growth annually. As a tree ages, the increase in height gradually slows. After about 5-7 years, most of the plant’s energy is diverted to increasing trunk and branch diameter (as much as 50 cm annually) and lateral branch growth. The life span of a tree usually exceeds several decades.

DISTRIBUTION & HABITAT

H. tiliaceus is a common coastal plant native to Australia, Oceania, and Southeast Asia. It was probably brought to the Hawaiian Islands by the first Polynesian colonists (as one of the “Canoe Plants”) and quickly became naturalized. Normally found at elevations ranging from sea level to 800 m, H. tiliaceus prefers areas that receive 35 to 95 inches of annual rainfall. It is well adapted to living in coastal environments and is common along beaches and river banks, and the inner margins of mangrove swamps.  It is able to tolerate salt spray and waterlogged and salt-saturated soils. Once established, it is very drought tolerant. It grows well in the coral and basalt sands that are common in the Hawaiian Islands.  It does best in soils that are slightly acidic (pH of 5) to alkaline (8.5). H. tiliaceus is able to tolerate a fair amount of shade (as much as 75 percent) because it can produce larger leaves; however, its growth rate slows considerably under these conditions. It prefers full sunlight. Although it is able to withstand high winds, this species does suffer a good deal of branch breakage during violent tropical storms. However, it recovers quickly after such damage, particularly because of the ability of its branches to bend to ground level and take root. In fact, modest stands of H. tiliaceus that have been virtually flattened by hurricanes have regenerated quickly, growing into impenetrable thickets.

Closeup of a Hau blossom.

TRADITIONAL USES IN HAWAII

H. tiliaceus has been and is culturally significant throughout the tropical Pacific. In Pre-Contact Hawaii, this plant was so valuable that one had to obtain permission from the local village chief to harvest it. Rubbing the pointed end of a hardwood stick in a groove cut into a piece of Hau wood was once the preferred method for starting a fire. The white timber is very boyant due to its low specific gravity (0.6), and it is light weight but extremely tough. Because it is so durable and boyant in seawater, Hawaiian canoe builders once used the wood of the Hau tree for the spars (‘iako)  and pontoons (‘ama) of their outrigger canoes (wa’a), and for fishing-net floats (mouo ). They also used the inner bark (or “bast”) fibers  to make a general-purpose cordage (kaula ‘ilihau) with very high tensile strength (which actually increased when wet). The rope was made by braiding together several long strips of the fiber; the number of fiber strips used depended upon the strength required by the user. The bast fiber was also used to make durable sandals. The sap from the inner bark was used as a laxative. The juicy sap found in the dome of the flowerbud and in the inner bark was used as a mild laxative. The flowers were also  eaten to aid in digestion and relive mild throat irritations caused by bronchitis and dry-throat. The flowers were (and still are) used in making flower leis because of their bright yellow color and the fact that they are available year round.

The characteristic heart-shaped leaf of Hibiscus tiliaceus.

Although it is not recognized as a commercially important species, H. tiliaceus has some traits that are beneficial to its environment. Its dense branches and foliage make it an ideal windbreak, hedge, or boundary plant. Well-established stands of this tree actually improve soil fertility by adding valuable organic matter by means of leaf drop, which occurs in large quantities year round. The long spreading branches are able to take root where they touch the ground, thus helping to stabilize soil on slopes, along river banks, swamps and mangroves, and exposed sandy shorelines. It some regions, this species has been used to stabilize eroding sand dunes.

INVASIVE CHARACTERISTICS

Although it is not classified as a nuisance species, H. tiliaceus does produce a complex tangle of highly invasive, laterally-spreading roots. In addition to producing a large number of suckers from the roots, the root system has a well-deserved reputation for severely damaging irrigation pipes and sewer lines, concrete walks, fences, and building foundations.  The major drawback of this species is that it is extremely difficult to eradicate once it has become established. In addition, its ability to become naturalized in well-watered environments and reproduce rapidly by both vegetative growth and seed propagation enables it to crowd out crop plants and native plant species by creating a shade-producing tangle of surface roots, branches, and foliage.

Torch Ginger (Etlingera elatior), Hana, east Maui.

Aside from being the ideal subjects for amateur photographers (unlike birds and whales, they tend not to move around much), the various species of ginger have long been known for their aromatic properties and as an ingredient in prepared ethnic foods. More recently, many “root ginger” species that belong to the taxonomic family Zingiberaceae have been found to possess chemical compounds sought after by the pharmaceutical industry. Zingerone, gingerols, and shogaols are the volatile oils (about three percent by weight) responsible for ginger’s fragrance, distinctive taste, and numerous beneficial medicinal properties.

Several extracts and distillations of ginger plants possess antibacterial, analgesic, sedative, and antipyretic (fever-reducing) medicinal properties. In addition, several species of ginger are currently being researched as candidates for the treatment and cure of skin and ovarian cancer. There is also on-going research into the blood-thinning and cholesterol-reducing properties of ginger. Powdered ginger root capsules have been shown to be effective in treating and preventing the nausea associated with morning sickness and motion sickness; however, clinical studies in this area have proven inconclusive.

The English word “ginger” comes to us from the French word “gingimbre” by way of the ancient south Asian words “inji ver” (literally, “the root of Inji” in Dravidian) and “singivera” (Pali), from which the Greek word “zingiberis” and the medieval Latin word “gingiber” probably were derived. As you might expect, the Hawaiian names for individual species of ginger evolved along a different linguistic line.

The following are a few of the most common species of ginger plants growing in Maui’s gardens and rain forests. (Note: To see more photographs of ginger plants on Maui, click HERE.)

Close-up of the inflorescence of a Torch Ginger (Etlingera elatior), Hana, east Maui.

Torch Ginger (Etlingera elatior), Hawaiian = ‘awapuhi ko‘oko‘o – A herbaceous perennial, individual plants grow in large clumps whose stalks can be as much as 6 m high with leaves as long as 85 cm. The leaves grow from separate evergreen stalks spaced out in ranks along individual rhizomes (an underground stem, usually growing horizontally). The inflorescence or flower-bearing part of the plant is glossy red with red flowers that have yellow margins. It rises directly out of the rhizomes to a height of about one meter. Individual flowers appear from between the scales (floral bracts) of the bright reddish-green pine cone-like inflorescence. The fruit is a green or reddish-green globe 2-3 cm in diameter containing numerous small black seeds.

Although it is cultivated throughout the tropics and has escaped to become naturalized in some localities, its original native range is thought to be a few isolated islands in Indonesia.  Typically it prefers a moist climate with somewhat acidic soil (pH = 5.6 to 7.5). It prefers full sun but does well in the partial shade of the rain forest. It is found at altitudes up to 9,000 feet.

The various plant tissues and parts of this species of ginger are rich in volatile aromatic compounds. The majority of the essential oils extracted from the leaves, stems, flowers, and rhizomes of Torch Ginger are monoterpene hydrocarbons. Terpenes are the primary constituents of the essential oils of many types of plants and flowers. Essential oils are used widely as natural flavor additives for food, as fragrances in perfumery, and in traditional and alternative medicines. Synthetic variations and derivatives of natural terpenes and terpenoids also greatly expand the variety of aromas used in perfumery and flavors used in food additives. Vitamin A is an example of a terpene. Currently, this and other species of ginger are the subjects of extensive research into the various antioxidant compounds present in their leaves and rhizomes.

Crepe Ginger (Costus speciosus), Hana, east Maui.

Crepe Ginger, Malay Ginger, Spiral Flag, Wild Ginger (Costus speciosus) – Crepe Ginger is a native of the Greater Sunda Islands of Indonesia and the Malay Peninsula. Although it has become naturalized in the Hawaiian Islands, its invasive tendencies enable it to crowd out native species. Its preferred habitat is moist fertile soils and partial sun, but will grow well in full sun if it gets plenty of moisture. One of the most cold-hardy of the gingers, it has been shown to withstand freezing temperatures as low as 17 degrees Celsius. Crepe Ginger is a tall and substantial-looking plant with large (15-30 cm long by 5-7 cm wide) dark-green leaves arranged on the stalk in a spiral. This species can grow to more than 3 m tall under ideal soil and climatic conditions. The unusual-looking flowers bloom throughout the year in tropical climates, but only in late summer to early fall in colder conditions. The flowers are borne on distinctive dark-red pine cone-shaped bracts (10 cm long) with several white crinkled flowers (5 cm long) conspicuously protruding from each cone. The flowers’ petals look like crepe paper, hence the common name “Crepe Ginger”. After the flowers wilt and drop, the red cone-shaped bracts remain. The fruit is a globular capsule containing many of the small black and white seeds. Although fruit-eating birds consume and scatter the seeds, this and other ginger species propagate more effectively by producing a large network of thick fleshy rhizomes that are similar in appearance to the “ginger root” sold in grocery stores and at farmer’s markets. A single rhizome will produce new shoots and grow into a clump more than one meter in diameter in less than two years. Traditionally, the  rhizome has been used to treat fever, rash, asthma, bronchitis, and intestinal worms. In India and Southeast Asia, this species is still used to treat boils, constipation, diarrhea, dizziness, headache, and vertigo. This species is also a source of diosgenin, a compound used for the commercial production of clinically important steroids such as progesterone.

White Ginger (Hedychium coronarium), Hana, east Maui.

White Ginger, Ginger Lily (Hedychium coronarium), Hawaiian = `awapuhi ke`oke`o – A native of India, it was exported throughout the tropics because of its popularity as an ornamental species. It soon escaped the confines of private gardens and became naturalized throughout the Hawaiian Islands. It is considered an invasive weed because of its ability to propagate quickly by sending out many shallow roots (rhizomes) in all directions, creating dense thickets of individual plants. This creeping growth quickly overwhelms and crowds out other low-growing plant species. Hedychium coronarium is a perennial herb that can grow as two meters in height. It prefers moist habitats, such as rain forests, the banks of streams, moist forest, roadsides, and open fields and pastures. It has large (30 cm long by 10 cm wide at maturity) simple elliptical or lance-shaped leaves.  It produces large numbers of flowers throughout the year. The fragrant white flowers are borne on long (10-20 cm) elliptical spikes in groups of two to six flowers atop a leafy stem.  The fruit is borne in an oblong many-seeded capsule, but is not usually present or easily seen since propagation of the species is usually accomplished by spreading rhizomes.

Indonesian Wax Ginger (Tapeinochilos ananassae), Hana Maui Botanical Garden, east Maui.

Indonesian Wax Ginger or Pineapple Ginger (Tapeinochilos ananassae) – Like other ginger species growing in Hawaii, this plant was introduced for its ornamental attributes: a large, showy inflorescence and beautiful foliage. Its foliage consists of thick, jointed bamboo-like stems that grow directly from numerous rhizomes. The long, smooth, lance-shaped leaves are arranged on the stem in an inward-curving spiral typical of this species; the leaves radiate outward from the spiral.  The small yellow flowers (which function as attractors to pollinating insects and birds) are aggregated in a large (10-30 cm long), bright-red pineapple-shaped terminal spike consisting of what appear to be waxy bright red flower petals, but are actually bracts (modified leaves that enclose the actual flower). To reach its full height (about 3 m), this species requires very high humidity. It prefers the full shade and moist, fertile, well-drained soils of the rain forest. Unlike many other tropical ginger species, this plant possesses no aromatic essential oils.

Scarlet Spiral Flag Ginger (Costus woodsonii Maas), Hana Maui Botanical Garden, east Maui.

Scarlet Spiral Flag Ginger, Indian Head Ginger, or Red Button Ginger (Costus woodsonii Maas), Hawaiian: ‘awapuhi ‘inikini po‘o – This species has gently spiraled stems and grows to about a meter in height. The leaves are deep green. The bracts of the inflorescence are bright waxy red, forming a pine cone-like spike (10-15 cm long) from which the yellowish-orange flowers protrude outward one at a time. The numerous small black seeds (1-2 mm long, the smallest of the true gingers) are usually dispersed by birds, but it is possible that they are also dispersed by water if the plant is growing in a wetland environment. C. woodsonii is an aggressive and invasive species. Its rhizomes spread rapidly and, once established, they are difficult to remove.  This species grows well in full sun, flourishing even in the sandy soils and dune sands of tropical coasts, but it prefers the shade, ample moisture, and deep, fertile soil of the rain forest. Although the genus Costus sp. is found throughout the tropics on all continents, this species was first collected and described in Panama in 1941. It was an introduced ornamental garden plant that became a naturalized escapee in some parts of Hawaii. It is considered to be an invasive weed on Oahu, Maui, and Kauai islands. It is present in large but widely scattered populations at low elevations on Maui, particularly along the Hana Highway. This species also displays a classic behavior of species mutualism: it exudes what is known as “extrafloral nectar” from the bracts of the flower spike, attracting ant species that harvest the nectar. In turn, the ants protect the plant from the larvae of flies and other flying insects that lay their eggs in the flowers.

The pink variant of Red Ginger (Alpinia purpurata), a garden in Kihei, south Maui.

Red Ginger (Alpinia purpurata), Hawaiian = ‘awapuhi ‘ula‘ula – Originally a native of Southeast Asia, A. purpurata was introduced to Hawaii as an ornamental species in 1928; it is now naturalized. Grows to about 3 m tall in the wild (can grow to more than 9 m tall under cultivation) and forms large clumps of foliage bearing large oblong leaves (30-80 cm long by more than 20 cm wide).  As with other ginger species, the large inflorescence (15-30 cm long, getting longer as the plant ages) consists of brightly colored (usually pink or red, occasionally white) bracts that look like a bloom, but the true flower is a small white blossom (corolla) at the outermost tip of the inflorescence. The fruit is a globular seed capsule about 3 cm in diameter that contains numerous small seeds (2-3 mm long). Although this species of ginger will tolerate direct sunlight, it requires very high humidity and soil moisture, as well as warmer air temperatures (more than 50 degrees F) to grow to its full size. Research has revealed that this species is a possible natural source for bioactive compounds useful for the treatment of hypertension.