Notes on Portulaca L. (Portulacaceae) in Tropical East Africa

Abstract

This paper arises from the preparation of the account of Portulacaceae for the Flora of Tropical East Africa. Many species from East Africa are based on the Tanzanian collections of the German botanist A. Peter and described by him in his Flora von Deutsch Ost-Afrika (1938). Von Poellnitz (1940), also working on Peter's material, described some additional species. However, these species names have hardly been used since, and the interpretation of some of them has caused problems, discussed below. Luckily much of Peter's material is still extant and available for consultation in the Berlin herbarium. Since the 1940s Portulaca collections from East Africa often either remained undetermined to species, or names of widely distributed species have been misapplied, particularly P foliosa Ker Gawl. and P kermesina N. E. Br. Part of the problem stems from the fact that variation within Portulaca is very little understood. Self pollination is the norm and leads to a multiplicity of local forms. The coastal lowlands and Tana River area of Kenya are particularly rich in Portulaca variants, whose significance is difficult to assess from the sparse herbarium material available. Two particularly distinctive forms are described here as new species. Additionally, a locally common yellow-flowered species from southern Kenya and northern Tanzania, which has been routinely misidentified as P foliosa, was found to be undescribed.