OVULE NUMBER, SEED NUMBER AND SEED SIZE IN MEXICAN AND NORTH-AMERICAN, SPECIES OF PODOSTEMACEAE

The purpose of this study is to present and analyze empirical data on seed production and seed characteristics of Mexican and North American species of Podostemaceae. Species of Marathrum, Oserya, Podostemum, T risticha and Vanroyenella were studied. Podostemaceae flower annually in abundance. Eight of the nine species examined produced seeds in abu ndance. Podostemum ricciiforme (Liebmann) Royen seldom produces seed. Significant differences occurred between annual and perennial species in mean ovule and seed number. In Podostemaceae, the outer integument of the seed plays a central role in the establishment of seeds on soli d substrate. Significant differences between species were observed whe n comparing overall seed width and length for dry versus wetted seed ( cf. percent contribution of the hydrated outer integument). In all spe cies there was a significant positive correlation between integument s ize and seed size. It remains to be shown whether the observed differe nces in seed characteristics are ecologically significant, e.g. equate with differences in microhabitat attachment, or reflect differential selection for seed establishment. Clear patterns of relationships betw een seed production and geographic distribution of species studied her ein are lacking. Questions that remain to be addressed concerning seed ecology are discussed. (C) 1997 Elsevier Science B.V.