Pollen morphological studies in the Malvaceae

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Abstract
Pollen grains of more than 120 species from c. 40 genera of Malvaceae were studied with light and scanning electron microscopy. The pollen grains are spiny, usually spheroidal and an evolutionary trend from a medium sized, ancestral 3-zonocolporate pollen type with small spines to a large polytreme type with long, sometimes distinctly dimorphic spines is recognised. The most simple of the intermediate types have the apertures spaced over the pollen surface creating a pattern very much like the seam on a tennis ball. This and other evolutionary trends in the pollen morphology are discussed in comparison with common classification, cytology and phytogeography of the family. A revised and simplified method for calculating the number of apertures on polyporate pollen grains is also presented. This method compensates for the spherical excess, inaccuracies arising from formulae which treat curved surfaces as flat.