Microsporogenesis in monocotyledons

This paper critically reviews the distribution of microsporogenesis types i n relation to recent concepts in monocot systematics. Two basic types of mi crosporogenesis are generally recognized: successive and simultaneous, alth ough intermediates occur. These are characterized by differences in tetrad morphology, generally tetragonal or tetrahedral, although other forms occur , particularly associated with successive division. Successive microsporoge nesis is predominant in monocotyledons, although the simultaneous type char acterizes the 'lower' Asparagales. Simultaneous microsporogenesis also occu rs in Japonolirion and Petrosavia (unplaced taxa), some Araceae, Aponogeton , Thalassia and Tofieldin (Alismatales), Dioscorea, Stenomeris and Tacca (D ioscoreales), and some Commelinanae: Arecaceae (Arecales), and Cyperaceae, Juncaceae and Thurniaceae (Poales). Simultaneous microsporogenesis is of ph ylogenetic significance within some of these groups, for example, Asparagal es, Dioscoreales and Poales. An intermediate type is recorded in Stemonacea e (Pandanales), Commelinaceae (Commelinales) and in Eriocaulaceae and Flage llariaceae (Poales). There is little direct relationship between microsporo genesis type and pollen aperture type in monocots (except for trichotomosul cate and pantoporate apertures), although trichotomosulcate apertures in mo nocot pollen, and equatorial tricolpate and tricolporate apertures in eudic ot pollen, are all related to simultaneous microsporogenesis. (C) 1999 Anna ls of Botany Company.