Palynological diversity of some species of Coussareeae (Rubiaceae) from the Atlantic Forest, Brazil

Abstract

Coussareeae is a neotropical tribe with a complex taxonomic history. Several authors considered it very close to the tribe Psychotrieae owing to similarities in their morphological characteristics, such as solitary ovules. The tribe Coussareeae constitutes the largest basal clade of the subfamily Rubioideae, and most of its genera are well represented in Brazil. The tribe is resolved into three suprageneric clades, including the Coccocypselum and Coussarea-Faramea clades, whose representatives are found in Brazil. This study aimed to ascertain whether pollen attributes corroborate the currently proposed phylogeny and systematics of the tribe. For this, pollen grains of 33 species belonging to the Coccocypselum and Coussarea-Faramea clades were analyzed. Specimens were obtained from herbaria, treated by the acetolysis method, measured, photographed, and described using light and scanning electron microscopy. Morphological analysis showed that pollen grains were medium (25–50 µm) or large (50–100 µm) in size; isopolar or apolar; 2-porate, 3-porate, or 3-colporate; and oblate spheroidal, suboblate, prolate spheroidal, or subprolate. Ornamentation varied among clade representatives. Multivariate analysis of quantitative data revealed that pollen diameter, apocolpium side, pore diameter, colpus length, and endoaperture width were the most significant characters. It can be seen from the results that the studied clades are formed by palynologically distinct genera in terms of polarity, aperture type, and ornamentation. Palynology confirms the proposed taxonomic classification.