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a: monocolpate type (Convallaria majalis). It is the most common type of monocotyledons. b, c: tricolpate type (Aspazoma amplectens, Aizoaceae; b equatorial view, c: polar view). The tricolpate type is the chief pollen type of dicotyledons.
g: A typical pollen of Asteraceae with a spiky (echinate) surface (Bellis perennis), h is the same specimen as g, but photographed in side view. The pollen grain is tricolpate. i: Taraxacum officinale
To the left: Pollen tetrad. The structures of proximal and distal poles differ often. These differences are an important feature of classification (Rhododendron). To the right: Pollen polyad. The products of several pollen mother cells stay together and form one distribution unit (Acacia) (H. D. IHLENFELDT, V. BITTRICH, M. STRUCK, 1986).