Floral displays, such as the color, shape, size, and arrangement of flowers, are typically thought to have evolved primarily in response to selection by pollinatorsfor animal-pollinated species, being able to attract animal vectors is vital to an individual plant's reproductive success. But can herbivores also exert similarly strong selective forces on floral characters? New research on two sister species in South Africa suggests that this may indeed be the case for inflorescence architecture in the rat's tail plant, Babiana ringens. By modifying the primary location of its floral display in response to pressure from mammalian herbivores, B. ringens may have not only reduced floral herbivory, but may also have enhanced pollination by providing a specialized perch for its principal pollinator.
Endemic to the Cape region of South Africa, Babiana ringens produces bright red flowers that are situated close to the ground on an unusual inflorescence axis that protrudes above the floral display. Its primary pollinator, the malachite sunbird, is attracted to the flower's red color and abundant nectarthe color, shape (tubular), and size of the flowers indicates that these characters likely evolved in response to sunbirds. In previous research, Bruce Anderson (University of Stellenbosch, South Africa) and colleagues discovered that the protruding modified inflorescence axis serves as a perch for sunbirds, allowing them to turn upside down in a perfect position to access nectar and facilitate pollination.
In Babiana ringens, the inflorescence axis is modified such that growth of the apical side branches is suppressed and flowers are only produced on a single branch at the ground level. A close sister species, B. hirsuta, exhibits similar inflorescence morphology, except that flowers are produced on side branches all along the stalk and not just at the base.
Caroli de Waal, a graduate student at the Univers
|Contact: Richard Hund|
American Journal of Botany