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Not a shrinking violet: Pollen morphology of Violaceae (Malpighiales)

Abstract Pollen morphology of Violaceae, a family of c. 825–900 species, has been little studied to date, with the exception of Viola. In this paper, we present the results of a survey of the pollen of representative species of 16 of the 23 genera of Violaceae, examined using light microscopy, scanning electron microscopy and selectively transmission electron microscopy. Pollen grains are isopolar monads with a mean polar diameter of 30.2 μm and a mean equatorial diameter of 34.1 μm. Unusually, two size classes were found in pollen of Fusispermum. The shape of Violaceae pollen is mostly suboblate or oblate spheroidal with an obtuse convex triangular amb. The apertures are tricolporate with the exception of Paypayrola where the pollen observed was dicolporate, and the endoapertures are mostly lalongate pores. The pollen surface is usually perforate and granular. The exine is tectate perforate and columellate, usually with thickened endexine at the apertures. Pollen descriptions are provided for 21 taxa representing most of the lineages in the phylogenetic tree produced by Tokuoka in 2008 using both plastid and nuclear genes. Pollen characters were optimised on this phylogeny using parsimony and our results indicate the high potential utility of pollen characters in the systematics of Violaceae.