A Difference in Pollen Size Between the Male and Hermaphrodite Flowers of Two Species of Apiaceae

Abstract

The size of pollen grains from male and hermaphrodite flowers was compared in two species, Lignocarpa diversifolia (Cheeseman) J . Wyndham Dawson and Gingidia harveyana (F. Muell.) J . Wyndham Dawson (Apiaceae). In L. diversifolia, pollen grains from hermaphrodite flowers were on average 20% greater in volume than the grains from male flowers; in G. harveyana, pollen grains from hermaphrodite flowers were on average 13% greater in volume than grains from male flowers. There was also considerable variation in pollen size among flowers of each type, both within and among plants of both species. Conditions during pollen development could be important; the early arrest of development of the gynoecium in male flowers could have a general effect on the flower and result in smaller pollen. Alternatively, the size difference could be adaptive if pollen from hermaphrodite flowers fertilises flowers with longer styles than does the pollen from male flowers. The size difference also could result from selection for an increased number of pollen grains in male flowers if there is a trade off between pollen size and number.