Pollen micro-morphometry of two endangered species of Rauvolfia L. (Apocynaceae) from the Indo-Gangetic Plains of Central India using LM, CLSM and FESEM

Abstract

Rauvolfia belongs to the family Apocynaceae and encompasses herbs or shrubs with leaves in whorls of three or four. It is an endangered plant of the tropics and subtropics. We present a preliminary study and analysis of the morphological details of the pollen of two extant species of Rauvolfia (R. serpentina (L.) Benth. ex Kurz and R. tetraphylla L.) from the Ganga Plain using light microscopy (LM), confocal laser scanning microscopy (CLSM) and field emission scanning electron microscopy (FESEM). The critical point drying method (CPD) was adopted to test the pollen size difference from the conventional acetolysis method (ACE). The pollen morphology of R. tetraphylla differs from that of R. serpentina in several specific traits. Its pollen grain is 3-colporate; it is oblate to oblate-spheroidal; sexine is punctate to obscure and mostly as thick as nexine; and a distinct thickening is present around the ectocolpi. The study shows that R. serpentina can be distinguished from R. tetraphylla by its pollen shape, size, sexine ornamentation (particularly the presence and absence of punctae/perforations in the mesocolpial region) and length of the ectocolpi thickening. The pollen shape and aperture number are more or less common features in Rauvolfia spp., but the presence and absence of a punctate pattern at the mesocolpial position marks the primary difference between the two species. The t-test was applied to determine the statistical significance of pollen morphological data of both species. This study provides a source of information for systematic and conservation purposes and provides a baseline to facilitate palynological studies of past vegetation and palaeoenvironments.