Diatom types of R.E.M. Archibald from Lake Sibaya and Lake Nhlange, South Africa

Abstract

Natural lakes are rarely found in South Africa and are usually restricted to coastal regions. One of the larger coastal lakes is Lake Sibaya, which is situated in North-Eastern Kwa-Zulu Natal, a subtropical summer rainfall region. In 1966 a survey of this and other smaller lakes connected to the Lake Sibaya system was conducted and diatom samples were collected, of which three were examined by R.E.M. Archibald, and from which nine new species were described. Archibald illustrated these new taxa using line drawings; the interpretation of such illustrations for species identification is sometimes difficult. For this reason we have re-examined the type material with the aim of producing light microscope (LM) and scanning electron microscope (SEM) micrographs of the species in question. All nine taxa described and illustrated by Archibald were found again in the type slides and photographed from the holotype slides using LM. Unfortunately the preserved type material was stored in un-buffered formalin and had degraded to a point where it could no longer be used for SEM. Additional desiccated samples collected during later expeditions between 1966 and 1972 were selected, based on similarity of locality and substratum, and used to obtain SEM micrographs. Again, all taxa could be documented from material in these additional samples. Of the nine taxa described, we transferred four to more appropriate genera, as they were originally described as species of Achnanthes and Navicula. Although Archibald’s line drawings were detailed and accurate, it was necessary to document these types using LM and SEM in order to make accurate designations at generic level and to facilitate identification of these taxa if found in other localities.