Prickly Pachypodiums

Although they resemble cacti, these African plants evolved independently from their American look-alikes.

Madagascar may be best known for its lush jungles and endangered lemurs, but the deserts along the island's west coast host another set of equally endangered species - Pachypodium plants. True to their name, which means "thick foot," these prickly plants survive hot, dry climates by storing water in thick, tuberous trunks. With this adaptation, many Pachypodium species can survive temperatures of over 150° F, which can arise in rocky areas along the country's west coast. One of these species, Pachypodium baronii, which occurs in only two small regions in the northwest corner of the country, is particularly endangered since its spectacular red flowers make it a target for plant poachers.

Although Pachypodium spines may not stop human poachers, they do prevent most other predators from accessing their precious moisture stores. This adaptation presents a close parallel to the thorny cacti of North and South America. Although both types of prickly plants exhibit many of the same survival tactics, they arose independently on separate continents. Scientists consider this example to be a classic case of convergent evolution, where similar environments or survival pressures cause unrelated species to evolve matching adaptations.

Map
Map by Colleen Sudekum

 

Isalo Elephant's Foot (Pachypodium rosalatum var. gracilius)
Isalo Elephant's Foot (Pachypodium rosalatum var. gracilius) from Isalo National Park, Madagascar.
Photo: Gerald and Buff Corsi; CAS Special Collections
Pachypodium Tree (Pachypodium lamerei) near Ihosy, Madagascar.
Pachypodium Tree (Pachypodium lamerei) near Ihosy, Madagascar.
Photo: Gerald and Buff Corsi; CAS Special Collections
1996 stamps dedicated to imperiled plants, including Pachypodium baronii
Beginning in 1993, the United Nations initiated an annual series of stamps depicting the world's most endangered plants and animals. The 1996 stamps are dedicated to imperiled plants, including Pachypodium baronii.