Palynological contribution to the systematics and taxonomy of Bauhinia s.l. (Leguminosae: Cercideae)

- This is a pollen study of Bauhinia s.l., an early branching lineage in the Leguminosae.
- The systematic and taxonomic importance of pollen morphological structures is examined.
- Pollen grains of the first branching lineages in the Cercideae are unspecialised.
- Specialised structures are found in Schnella, Lasiobema, Phanera, Piliostigma and Bauhinia s.s.

Pollen grains of 250 samples of taxa in the Cercideae clade have been studied using light microscopy, scanning electron microscopy and transmission electron microscopy. This study examines how pollen morphological structures can be used as taxonomic characters in systematic studies. Pollen grains of the first branching taxa in the Cercideae phylogeny, such as Cercis and Adenolobus, are unspecialised; they are isopolar, tectate, tricolporate, and released in monads. Surface ornamentation may be micro-reticulate or perforate, and psilate to rugulate. Aperture membranes are granular to coarsely granular. More specialised pollen grain structures are found in Schnella, Lasiobema, Phanera, Piliostigma and most of Bauhinia s.s. Pollen morphology is presented in a table for comparative purposes and illustrated, discussed and compared. Six specialised pollen structures described and identified are diagnostic for groups of related species in the Cercideae. These include a granular infratectum, syncolporate apertures, pororate apertures, spiny opercula, tetrads, and non-supratectal spines. Porate apertures occur in Phanera, Piliostigma and Bauhinia picta. Five pollen structures have been identified within the Cercideae clade that is restricted to Bauhinia s.s. These include striate ornamentation, having more than three apertures per grain, apertures that are indistinct, and colpate apertures. Supratectal ornamentation, structures such as gemmae, verrucae and striae, occur in many species in the Cercideae, as well as throughout subfamily Caesalpinioideae, and the functional implications of this are discussed. Pollen morphological structures are discussed with regard to systematic significance, taxonomic utility, and in relation to functional and developmental considerations.