I spend a lot of weekends scrambling over the dry leeward slopes of Maui’s Haleakala volcano, so I’ve become familiar with many of the odd assemblage of native and non-native plant species that have adapted to and flourished in that harsh environment. The rocks of the old lava flows that form the slopes weather slowly (due to the sparse rainfall and the resistant nature of basalt) and have yet to produce an appreciable soil horizon. What soil there is consists of coarse gravel poor in nutrients and unable to retain moisture near the surface. The harsh year-round glare of the sun on the black basalt of the lava flows and the region’s strong prevailing winds combine with the sporadic rains and nearly-absent soil to make a habitat inhospitable to all but the hardiest plant species.
The species that have successfully colonized Haleakala’s southern slopes have evolved many different strategies for coping with the adverse conditions, including mechanisms and behaviors for perpetuating the species.
A Mother of Millions Plant at home on the rocks.
The Mother of Millions (Kalanchoe delagoensis), one of my favorite drylands species, is no exception to this rule for survival. This odd little succulent goes by several different taxonomic names, including Bryophyllum delagoense. The Bryophyllums are a section of the genus Kalanchoe (a member of the Crassulaceae family). In botany, a section is a low-level taxonomic rank (below subgenus) used to organize large genera that include hundreds of species. The taxonomic nomenclature for this species has become a bit confusing: Bryophyllum delagoensis and B. delagoense are still cited as being synonymous with K. delagoensis in the print and online literature. For the purposes of this blog posting, I defer to the name cited in the United States Department of Agriculture’s National List of Scientific Plant Names.
Habitat
Although it is an introduced non-native species, K. delagoensis is naturalized in Hawaii. It is well adapted to the dry, semi-arid climate of the leeward slopes of the larger islands like Maui. It prefers gravelly and sandy soils with good drainage at low elevations (below 2000 feet). It flourishes in the intense sunlight found on open scrublands and bare lava outcrops. It also grows along stream drainages where it is spread by flood waters.
An immature Mother of Millions Plant displaying plantlets on its leaf tips.
Description
Kalanchoe delagoensis is an erect perennial succulent herb with long (3-15 cm long, 0.3-0.6 cm wide), fleshy pale yellow to grey-green tubular leaves with dark-green mottling. At the tip of each leaf are four or five small, pale-green spoon-shaped projections (bulbils) that, when broken off, can develop into new plants. The attractive orange to scarlet-red flowers (about 3 cm long) occur in a 10-20 cm-wide candelabra-shaped cluster (known as an “umbel”) at the top of a single unbranched stem that usually is more than 60 cm tall. Flowering can occur from May to October.
New blossoms on a mature Mother of Millions Plant.
Reproduction
As the name “Mother of Millions” suggests, K. delagoensis reproduces rapidly in one of two ways: (1) by producing hundreds of tiny viviparous plantlets at the tips of its leaves that separate from the parent plant and take root immediately, and (2) by producing seeds that can remain viable in the soil for several years. The maturing plant continues to grow for about 3 to 7 years. At the end of that time, the plant forms a robust terminal inflorescence; shortly thereafter the entire plant dies. Given the fact that a single plant can produce hundreds of viable offspring a year using both methods, it’s easy to see how this species can easily produce colonies of thousands of individual plants and how it came to be classified as a noxious invasive weed in Australia and on many tropical islands in the Pacific Basin.
A colony of K. delagoensis covering a lava flow on south Maui.
Toxicity as a Defense Mechanism
In addition to high-speed reproduction, K. delagoensis employs a passive defense mechanism to ensure its survival. Its foliage and flowers contain large quantities of bufadienolides (bufadienolide cardiac glycoside), a substance that can cause cardiac poisoning resulting in sudden-onset heart failure in grazing animals. In 1997, 125 head of cattle died after ingesting Mother-of-Millions plants growing on a stock reserve near Moree, in New South Wales, Australia. While the toxins are present in sufficiently lethal quantities in all parts of the plant, its flowers are five times more poisonous than the leaves and stems. Livestock poisoning generally occurs when the plants are in bloom between May and October. Mother of millions is also toxic to humans: secondary poisoning can occur in humans who eat meat from livestock that graze on K. delagoensis.
Tags: Bryophyllum, bufadienolide cardiac glycoside, bufadienolides, Chandelier Plant, invasive species, Kalanchoe, livestock poisoning, Mother-of-Millions, succulents, toxic weeds, weeds of Hawaii
