Asclepias, Lantana, and Epidendrum: A Floral Mimicry Complex?

Abstract

It has been suggested that Asclepias curassavica, Lantana camara, and Epidendrum radicans, three unrelated tropical weeds with very similar flowers, comprise a floral mimicry complex. Asclepias and Lantana are presumed to be of each other while the nectarless Epidendrum is thought to be a of the first two. Although the three species have overlapping ranges and share pollinators, visitation frequencies in stands of different floral composition do not support this hypothesis. Flowers in high-density stands of the Miillerian mimics are not visited more often than flowers in low-density stands, so apparent increase in population density through mimicry does not appear to confer an advantage. The Batesian mimic is not visited more often when interspersed with the model than when alone. Other possible reasons for the resemblance are discussed. Two OF THE MOST CONSPICUOUS ROADSIDE WEEDS in tropical America are Asclepias curassavica (Asclepiadaceae) and Lantana camara (Verbenaceae). Their red and yellow inflorescences are strikingly similar. Both species produce nectar and attract many species of potential pollinators. Epidendrum radicans, a terrestrial orchid that also bears clusters of bright red and yellow flowers, is somewhat less common. Epidendrum produces no floral nectar. Since the pollen grains of orchids are massed into pollinia that adhere to an insect's back, legs, head, or proboscis, and are thus unavailable to it as food, biologists have wondered how Epidendrum secures pollinators. An unpublished but widely circulated hypothesis is that these three plant species form a floral mimicry complex. Asclepias and Lantana are thought to be whose resemblance allows them to attract more pollinator visits, through the combined impact of their floral displays, than either would solely on the basis of its own abundance. Epidendrum, on the other hand, might be a mimic, obtaining visits by resembling the nectar-producers, Asclepias and Lantana. It has been demonstrated theoretically that the fitness of a rare plant species can be increased by the addition of another species with similar flowers, if pollinators do not distinguish between the two (Bobisud and Neuhaus 1975). In this case the advantage arises because the apparent increase in population size which results from the addition of the second species makes it more likely that a pollinator will specialize on that 'morphospecies (actually both species combined). The existence of a number of similar species pairs has been so explained (Schelpe 1966, Yeo 1968, Macior 1970 and 1971, Proctor and 1Present address: Department of Biology, Pomona College, Claremont, California 91711, U.S.A. 54 REPRODUCTIVE BOTANY 54-58 1981 Yeo 1972, Gentry 1974, Heinrich 1975, Lack 1976, Dafni and Ivri 1979), but without proof. Asclepias, Lantana, and Epidendrum comprise another such