New species and combinations on Fragilariforma (Bacillariophyta) from tropical freshwater environments

Abstract

Several species currently belonging to the genus Fragilariforma D.M. Williams et Round are known worldwide. This genus is mainly characterized by regular spacing of the uniseriate striae composed of round areolae bearing simple vela, and simple apical pore fields. A large number of species has been recognised for some regions of South America and tropical Africa, but few studies encompass type material and/or the morphological variation existing within populations of the different species. The aim of this study is to identify and describe the morphology of these species from tropical environments under light and scanning electron microscopy and using available type material. Nomenclatural issues are examined and clarified for five taxa: Fragilaria nitzschioides var. brasiliensis Grunow, F. undata var. brasiliensis C. Zimmermann, F. strangulata (Zanon) D.M. Williams et Round, F. telum J.R. Carter et Denny and F. rolandschmidtii Metzeltin et Lange-Bertalot. The type material of F. nitzschioides var. brasiliensis, housed in the Grunow Collection at the Naturhistorisches Museum Wien (W) was examined and its epitypification is proposed. One new species from the Amazon region Fragilariforma amazonica sp. nov. is presented and described here, while Fragilaria telum is formally transferred to the genus Fragilariforma.