Kalanchoe (the h is silent and the last e is not) is a genus of over 150 species of arid-adapted succulents mostly native to Madagascar and some to eastern and southern Africa. The family of the genus, Crassulaceae, contains hundreds of drought-resistant, succulent species adapted to desert or near-desert conditions, or to areas with long hot, dry seasons.
Many species of Kalanchoe have been introduced outside their native range because of their easy cultivation, and their tolerance of poor soils and dry conditions. Some have striking flowers and all are capable of multiply asexually with great ease. Many species in the genus produce fully formed plantlets from stems and leaf margins of adult plants that are still rooted. This capability, termed vivipary, is unusual among higher plants but can also be found in some species of mangrove.
Some of the cultivated species of Kalanchoe have successfully invaded habitats outside their native range where they outcompete indigenous species, often displacing them. The problem is especially troublesome on many Pacific islands but also in subtropical continental areas of Asia, the Americas and in Australia. In some of the colonized areas, Kalanchoe is not restricted to arid areas, but adapts readily to all but the wettest climates. The most invasive species may be K. delagoensis, (in older sources known as K. tubiflora) which rarely flowers but is rampant asexually. It also can survive in the warmest areas of the United States. A second pest species, K. pinnata (formerly Bryophyllum) is readily viviparous and has spread across most of the tropics of the world except the extremely dry and the extremely wet areas. A third species, K. daigremontana, is established in Puerto Rico, Hawaii and parts of peninsular Florida.
Kalanchoe flowers consist of parts in fours (floral formula 4-4-8-4)- a calyx of four sepals, a corolla of 4 partially joined petals, an urn-shaped gynoecium (female element of a flower) consisting of four units (collectively called the pistil), each with a stigma and style, and an androecium with eight stamens that occur in two series. The stamens include pollen-producing anthers with narrow filaments that are attached to the bases of the petals. Also present are four basal nectary glands which are of interest to nectar-eating birds and insects. All these parts are visible in the attached photographs from my yard of K. gastonis-bonnieri, a species with relatively large flowers.
Kalanchoe flowers generally are nodding. Although nodding flowers, especially in the absence of a “landing platform” which would allow other birds access to flowers, are often associated with hummingbird pollination, many nodding flowers, if not red and long-tubular, are pollinated by insects. Depending on species, pollination in Kalanchoe has been attributed to bees, ants, butterflies and to birds.
The genus Kalanchoe is considered self-incompatible meaning that an individual plant would require the pollen from another individual to set seed. Kalanchoe flowers are protandrous, i.e., the stamens of a given flower mature and release pollen before the stigma is receptive to pollen. In this way cross-pollination, which depends on the pollen of other flowers, is assured.
Seed production in Kalanchoe is variable in species and habitats while asexual reproduction is much more common. I have grown (or tolerated), hundreds of Kalanchoe plants from at least five species over ten years, and I have found none with seeds despite abundant flowering. An absence of pollinators may be involved. Because the plants are winter-flowering, fewer local pollinators would be available, or, possibly, the pollinators adapted to pollinating Kalanchoe in Africa are absent here. The Ruby-throated Hummingbird of the eastern U.S. is in its winter haunts when Kalanchoes flower in Florida. Some online sites do mention Kalanchoe flower visits by hummingbirds in the U.S., although whether cross-pollination is actually accomplished is unclear. Of course hummingbirds are not found in Africa although other families such as sunbirds (Nectariniidae) which are sometimes considered as ecological equivalents, are.
In addition to succulence as an adaptation to arid conditions, Kalanchoe species share with many other arid-adapted plants a distinctive photosynthetic pathway for CO2 assimilation that promotes water-use efficiency. Instead of absorbing CO2 from the atmosphere during the day when leaf pores (stomates) are open and leaf surfaces are warmed by sunlight as do most plants in humid climates, stomates of Kalanchoe plants open at night thereby reducing water loss while still allowing CO2 to be absorbed. The CO2 is stored as the 4 -carbon salt of malic acid in cell vacuoles. The malate serves as the carbon source for photosynthesis during daylight when the stomates are closed. The carbon is converted to energy-rich sugars which can be transported to other parts of the plant or metabolized in the leaf. This photosynthetic pathway is widespread among plant families that thrive in arid environments, but its frequency in the Crassulaceae and its elaboration in the Kalanchoe genus led to its being called Crassulacean Acid Metabolism (CAM).
Some Kalanchoe species (e.g. K. daigremontina and K. pinnata) are considered to be “facultative” CAM plants because they may or may not exhibit CAM depending on the growth environment. Drought conditions induce the CAM pathway while non-drought conditions do not. Having this flexibility can be regarded as adaptive where the plant grows in semi-arid environments that have both dry and wet seasons. Interestingly, modern Kalanchoe cultivars developed by horticulturalists under decidedly non-desert conditions, have lost their CAM ability and instead photosynthesize like plants typical of wet climates.
Problems arise when Kalanchoe plants are consumed by vertebrates because the plants contain glycosides including toxic cardiac glycosides (particularly cardenolides and bufadienolides), which interfere directly with electrolyte balance within the heart muscle. Dogs and cats are very susceptible to glycoside poisoning if they consume Kalanchoe leaves or flowers. Where Kalanchoe species are established in South Africa and Australia, cattle and sheep poisonings are common. A lethal dose in calves is 40 g of foliage and only 7 g of the more toxic flowers. Apparently, however, the presence of glucosides is not a deterrent to non-mammalian herbivores as seen in the photograph of partially consumed flowers from my yard.
Remarkably, some of the same glucosides found in Kalanchoe are found in Rhinella marinus, (formerally Bufo marinus) the giant cane toad that is a pest in many tropical and sub-tropical areas. This large amphibian is renowned for its “ability” to kill predators (including dogs) who bite it, because its skin contains lethal doses of bufadienolides. This commonality has led to a striking interaction. (Price-Rees et al., 2012). The spread of invasive Kalanchoe species through eastern Australia which began long before the arrival of Rhinella, imposed selection pressure for bufadienolides-resistance in native Blue-tongued Skinks which include both plants and animals in their diet. Lizards able to reproduce despite the glucosides in their diet (obtained by consuming Kalanchoe plants) produced a local population of lizards that could tolerate the later presence of the toad by virtue of their genetically-selected resistance to the glucosides- a good example of “preadaptation”. Meanwhile in western Australia, where the toad was introduced relatively recently (in 1935) and is less widely established, dramatic declines in skinks and several other predator taxa have occurred from glucoside-toxicity traceable to eating (or trying to) eat toads. Similar adaptation by native Australian black snakes to cane toad toxicity has also been documented.
cactuspedia.info/schedule/Kalanchoe/ Kalanchoe_delagoensis/ Kalanchoe_delagoensis.htm
Kluge, M.,B. Razanoelisoa, D. Ravelomanana and J. Brulfert 1992. New Phytologist 120: 323-334.
Ota, K. 1988 Stimulation of CAM Photosynthesis in Kalanchoe blossfeldiana by transferring to Nitrogen-deficient Conditions. Plant. Physiol. 87:454-57.
Price-Rees S.J., G. P. Brown and R. Shine 2012. Interacting Impacts of Invasive Plants and Invasive Toads on Native Lizards. The American Naturalist 179 (3)
Winter, K, M. Garcia and J. Holtum. 2008. J. of Experimental Botany 59:1829-1840.