Friday Fabulous Flower - Dead Stick Plant

Some plants do not attract much attention, sometimes because people only notice gaudy, sometimes because they are relatively uncommon or quite strange and people just don't know what to make of them, and sometimes because they are not meant to be noticed. The dead stick plant (Cynanchum marnierianum) is a leafless succulent consisting of long slender, pendent stems that look quite dead, perhaps the perfect houseplant. It has been suggested that the plant avoids herbivores by being so cryptic, but since its native habitat are dry forests of Madagascar, the coloration might simply be a filter for intense tropical sun. However if the dead stick plant is not indeed dead, then seasonally it bursts into bloom and the stems are covered with these delightful 1 cm diameter chartreuse bird cage flowers. The more taxonomically more sophisticated among you may immediately recognize the flowers as rather typical for members of the milkweed family which contains many stem and leaf succulents. This is what discounts the cryptic coloration story; milkweeds are usually pretty well protected against most herbivores. These plants actually do make good house plants if you have a sunny place for a hanging basket and like a bit of bizarre among your plants and can avoid over watering.

Pollination biology in the greenhouse

Every semester our greenhouse has one very busy week that is the result of all the students taking non-majors biology have a laboratory exercise involving the use of floral syndromes, suites of floral characters used to determine the likely pollinators of different flowers. Sometimes the plants cooperate by flowering, and sometimes they don't. Sometimes the students cooperate by being observant, and sometimes they don't. Probably no more than one in ten of the students has any appreciation of this experience, but for a few it's revelatory, in this case because of the cooperation of a few stunning plants. Here's one of my favorites, a star flower (Stapelia), a succulent member of the milkweed family. The flowers are large, some 10-15 cm diameter in this species, and the leathery corolla is hairy, sort of dried-blood colored, and has the wonderful floral fragrance of carrion. Look closely and you'll see that even some of our temperate zone flies are quite fooled by this mimicry, and indeed, eggs were deposited and young maggots (those little oblong whitish things) were looking for what their mother thought was carrion in vane because the flower does not deliver the goods promised. No brood substrate exists, but in looking for a place for their babies, pollen gets picked up and moved from fake carrion flower to fake carrion flower. Very astute students in more advanced classes may think to ask, "Why doesn't evolution work to alter the fly's perception such that they avoid fake carrion because any fly that does is not going to waste their reproductive potential. Well, they understand the concept OK, but what does it matter when flies are so numerous and carrion flowers so rare in comparison. The few flies involved, even if under very strong selection, will not affect the much larger gene pool to which they belong. In other words the plant can afford to fool a few flies without risking the loss of their pollinators from natural selection. Star flowers are nice houseplants, so long as you don't over water them, and they don't bloom! And yes, a few students were actually impressed, and extremely pleased that they correctly diagnosed fly pollination, and actually saw it in action.