EVOLUTIONARY ASPECTS OF WIND POLLINATION IN THE GENUS PLANTAGO (PLANTAGINACEAE)

Abstract

SUMMARYThe selective forces acting to maintain a copious production of uniformly sized pollen grains in wind‐pollinated plants were investigated among species in the genus Plantago and at the population level in P. lanceolata. The species with cleistogamous (closed) flowers produce far less pollen of more variable average diameters than the species with chasmogamous (open) flowers. Pollen grains of P. lanceolata captured by stigmas of female plants were smaller than a general sample of pollen collected from the anthers of perfect plants, indicating that large pollen grains are not as effective as small grains in wind dispersal. The rapid decrease in pollen density on the stigmas of P. lanceolata with increasing distances from the pollen sources suggests that plants of this self‐incompatible species must produce great amounts of pollen in order to pollinate nearby plants. The cost of this high pollen production associated with wind pollination can be seen in P. lanceolata in the increased production of reproductive tissue and larger seeds in female plants when compared with normal plants.