A taxonomic study of the acacia pollen grains in Kenya

Abstract

The genus Acacia which is the largestest in the subfamily Mimosoideae and second largest within the family Leguminosae, is one of the most widespread and important, having 38 indigenous species in Kenya. Its species are dominant and form an important component of the vegetation over extensive tracts of the Republic. All geographical divisions of Kenya as recognised by Flora of Tropical East Africa have several species of Acacia some of which are of economic importance. An attempt is hereby made to study the species using their pollen grains and the results have been compared with the classifications based on the nature of the stipules and the types of the inflorescences. The nature of the apertures, the pollen grain number and the exine stratification have been the major tools used to separate the Acacia species into two natural groups. The two groups have corresponded considerably well with sections Gummiferae and Vulgares of Bentham's classification (1842). Colporate and colummelate grains show a high de9ree of correlation with the spines cent species while the simple porate and granulate grains have correlated with the non-spinescent species. Acacia albida Del. has been found to be anomolous on the basis of pollen characters and has deviated from the Section Gummiferae under which it was classified by Bentham (1842). Its pollen grains show a remarkable difference from the grains under Sections Gummiferae and Vulgares. A compromise has to be reached on where to classify this species. The results suggest that a taxonomic category should be created to accommodate it. With the exception of Acacia albida a conclusion has been reached that a correlation exists between pollen characters and the classification outlined by Bentham (1842) on the African Acacia species