Pollen morphology and ultrastructure of Tephrosia Pers. (Leguminosae – Papilionoideae – Millettieae): a taxonomic approach for native and cultivated species in Brazil

Abstract

Previous palynological works on the genus Tephrosia involved only a small number of species though showed some discrepancies regarding morphological descriptions. Our study used a palynotaxonomic approach to analyse 13 species of Tephrosia (T. adunca, T. candida, T. cinerea, T. egregia, T. marginata, T. nitens, T. noctiflora, T. purpurea subsp. purpurea, T. domingensis, T. rufescens, T. sessiliflora, T. sinapou, T. vogelii), either native or cultivated in Brazil. Pollen was studied using light microscopy as well as scanning electron and transmission electron microscopy. Pollen grains are isopolar, small to large size, oblate to prolate, 3-colporate, mostly operculate with an ornamented colporus membrane. Sexine show a nanoreticulate to reticulate, microreticulate-perforate, rugulate-perforate, rugulate, psilate or psilate-perforate ornamentation; the sexine is thicker than the nexine. Exine consists of a compact tectum that varies from eutectate, tectate perforate to semitectate; the infratectum is collumelar or granular; the foot layer is discontinuous and endexine continuous. An unprecedented characterisation of the operculum, colporus membrane and granular structure of the infractectum in Tephrosia is described for the first time. The pollen morphology in Tephrosia is eurypalynous based mainly on the exine sculpturing that is the most variable morphological feature and also on the details of the aperture, which is important for infrageneric delimitation, and warrants attention in future phylogenetic analysis combining molecular and morphological data.