Taxonomic significance of the pollen morphology of family Combretaceae R.Br. (Myrtales) from Nigeria

Abstract

A comparative study of pollen morphological characters of 19 species of Combretaceae from Nigeria was undertaken with a view to obtaining additional characters for adequate identification and classification of the taxa. Pollen samples were acetolysed and investigated under light microscope. Hierarchical cluster analysis was employed to show the similarities and affinity among the Combretaceae species based on pollen-morphological features. All the species studied were monads, small to medium sized, radially symmetrical, heterocolpate with three simple apertures alternating with three composites. The exine showed various sculpturing patterns in all the taxa studied, namely, micro-rugulate, reticulate, scabrate, striate and psilate. The pollen size ranged from 10 to 50 μm. The largest pollen size (42.68 × 38.17 μm) was recorded in C. platypterum and the smallest one (14.75×15.05 μm) in C. sordidum. The species had prolate, sub-prolate and oblate-spheroidal pollen shapes. The dendrogram and bi-plot revealed nested grouping of the Quisqualis species within Combretum sub-genus Cacoucia. Palynomorphological characters of the studied species are considered highly diagnostic at the generic and specific levels. Therefore, pollen morphological data provide diagnostic information for differentiating Combretum platypterum and C. racemosum, C. zenkeri, C. smeathmannii, C. sordidum, Terminalia catappa and T. mantaly, which are morphologically similar species.