#holoparasite

Dodder species, most likely  Cuscuta campestris, the Field Dodder, growing and flowering in an open riperrian bed in Clifty Falls State Park, Indiana

Imagine hiking through the forests of Borneo and coming across this strange object. It's hairy, it's fleshy, and it smells awful. With no vegetative bits lying around, you may jump to the conclusion that this was some sort of fungus. You would be wrong. What you are looking at is the flower of a strange parasitic plant known as Rhizanthes lowii.

R. lowii is a holoparasite. It produces no photosynthetic tissues whatsoever. In fact, aside from its bizarre flowers, its doesn't produce anything that would readily characterize it as a plant. In lieu of stems, leaves, and roots, this species lives as a network of mycelium-like cells inside the roots of their vine hosts. Only when it comes time to flower will you ever encounter this species (or any of its relatives for that matter).

The flowers are interesting structures. Their sole purpose, of course, is to attract their pollinators, which in this case are carrion flies. As one would imagine, the flowers add to their already meaty appearance a smell that has been likened to that of a rotting corpse. Even more peculiar, however, is the fact that these flowers produce their own heat. Using a unique metabolism, the flower temperature can rise as much as 7 degrees above ambient. Even more strange is the fact that the flowers seem to be able to regulate this temperature. Instead of a dramatic spike followed by a gradual decrease in temperature, flowers are able to maintain this temperature gradient throughout the flowering period.

There could be many reasons for doing this. It could enhance the rate of floral development. This is a likely possibility as temperature increases have been recorded during bud development. It could also be used as a way of enticing pollinators, which can use the flower to warm up. This seems unlikely given its tropical habitat. Another possibility is that it helps disperse its odor by volatilizing the smelly compounds. In a similar vein, it may improve the carrion mimicry. Certainly this may play a role, however, flies don't seem to have an issue finding carrion that has cooled to ambient temperature. Finally, it has also been suggested that the heat may improve fertilization rates. This also seems quite likely as thermoregulation has been shown to continue after the flowers have withered away.

Regardless of its true purpose, the combination of lifestyle, appearance, and heat producing properties of this species makes for a bizarrely spectacular floral encounter. To see this plant in the wild would be a truly special event.

Photo Credit: Ch'ien C. Lee - www.wildborneo.com.my/photo.php?f=cld1500900.jpg

Further Reading:

http://www.jstor.org/stable/4222678?seq=1#page_scan_tab_contents