SYSTEMATIC SIGNIFICANCE OF POLLEN ARRANGEMENT IN MICROSPORANGIA OF POACEAE AND CYPERACEAE - REVIEW AND OBSERVATIONS ON REPRESENTATIVE TAXA

An anatomical survey of anthers of the Poaceae and Cyperaceae and two related families, the Restionaceae and Flagellariaceae, was conducted to determine the taxonomic distribution and possible phylogenetic sign ificance of pollen arrangement. An unusual pollen arrangement was know n from a small number of taxa in the Poaceae and Cyperaceae, in which a single, uniseriate cylinder of pollen grains is arranged in the anth er locule such that each grain is in contact with the tapetum (termed here ''peripheral'' pollen). This contrasts with the prevailing arrang ement in other angiosperms in which the locule contains a relatively l arge number of pollen grains in no special configuration, with many in terior grains that never touch the tapetum (termed here ''central'' po llen). A total of 48 species in these four families was examined in th is study, and observations on pollen arrangement for numerous addition al species in these families were gleaned from the literature. We conf irm that the peripheral arrangement is predominant in Poaceae and Cype raceae, although both families also include species with central polle n, whereas only central pollen is found in Restionaceae and Flagellari aceae. In the peripheral arrangement, the pore of the pollen grain or pseudomonad, when observed, is in contact with the tapetum, but it has not been definitively demonstrated that this is always the case. peri pheral pollen in the Poaceae and Cyperaceae is nonhomologous because o f the presence of pseudomonads in the latter family. It remains unexpl ained why peripherally arranged pollen or pseudomonads, with the atten dant reduction in the number of pollen grains, should be associated wi th anemophily in these two families.