Morphology of pollen and orbicules in some Dioscorea species and its systematic implications

Pollen and orbicule morphology of 35 Dioscorea L. species is described base d on observations with light microscopy, and scanning and transmission elec tron microscopy. Pollen and orbicule characters are critically evaluated an d discussed in the context of existing hypotheses of systematic relationshi ps within the genus. Pollen is mostly bisulcate (sometimes monosulcate) wit h a perforate, microreticulate or striate sexine. Our results indicate that pollen data may be significant at sectional rank. The close relationship b etween sections Asterotricha and Enantiophyllum proposed by Burkill and Aye nsu is supported by pollen morphology as all species investigated share bis ulcate, perforate pollen with small perforations and a high perforation den sity. Macromorphological differences between the two compound-leaved sectio ns Botryosicyos and Lasiophyton are also supported by pollen morphology; po llens of these two sections have very different perforation patterns. Orbic ules in Dioscorea are mostly spherical and possess a smooth or spinulose su rface. The latter is often correlated with a striate sexine. (C) 2001 The L innean Society of London.