The pollen morphology of 105 species of Saxifraga has been investigated. Four major types of sexine pattern are recognized, namely reticulate, granular, striate and very finely striate with superimposed granules or verrucae. The striate pattern is found to be the most common and is divided into eight subtypes. The types and subtypes are related to the sections recognized in the genus and are generally found to support the existing classifications. The pollen‐types also clarify some of the longstanding problems but leave others unresolved, and some exceptional patterns occur within otherwise well‐defined sections.
The surface sculpturing of the pollen of some species of the taxonomically widely separated genera Harpalyce (tribe Brongniartieae), Camoensia (tribe Sophoreae), Millettia (tribe Tephrosieae), and of the monotypic Dahlstedtia (tribe Tephrosieae) which have large red or white flowers adapted for pollination by birds or bats, is coarsely rugulate or verrucate. Related taxa with small insect pollinated flowers have pollen with simple reticulate or perforate surface sculpturing. The exine stratification of Alexa and Castanospermum (tribe Sophoreae), genera with large red bird‐flowers, is complex with a layer of tectal columellae and differs from that of other genera in the tribe Sophoreae which have a normal pollen wall structure. These modifications of pollen structure and sculpture appear to be the result of convergent evolution and a secondary adaptation to pollination. The taxonomic and functional significance of the observations are briefly discussed.
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