Pollen morphology of the genus Sophora (Fabaceae) and its taxonomic implications

The genus Sophora (Fabaceae) is one of the taxonomically challenging genera with high economic and medical values. In this study, the pollen morphology of 43 samples of 27 species, 4 subspecies, and 4 varieties of the genus Sophora and 3 closely related genera was examined using scanning electron microscopy to evaluate the pollen diversity of the genus and its taxonomic significance. Pollen grains of the studied species were tricolporate (rarely six-aperture), and pollen shape varied from suboblate, spheroidal, subprolate to prolate. Echinate external ornamentation was reported for the first time in some species of the genus. Aperture membrane ornamentation and outline in a polar/equatorial view were described for the first time in the genus. Principal component analysis was used to understand the relationship and discrimination between the species and the genera, with six components accounting for 79.92% of the total variance. Taxonomic keys based on pollen morphology were also constructed to easily identify the taxa of the genus through palynological characteristics. Results showed that pollen morphology alone is not sufficient to elucidate or reconstruct taxonomic relationships within the genus Sophora, but palynological assessments can provide some useful information for identifying taxonomically problematic taxa.