Tropical African diatoms from the Eunotia asterionelloides (Bacillariophyta) species complex, with descriptions of new species

Background and aims – Diatoms from tropical Central Africa are rarely studied and documented. Waters of the Congo Basin are often acidic and thus may be dominated by diatoms from the genus Eunotia, usually found in the benthos and periphyton, but rarely in the plankton. We investigated planktonic Eunotia species from the Eunotia asterionelloides complex to determine their identity and distribution. Material and methods – Samples were collected in fishponds in the vicinity of Kisangani, D.R. Congo, from herbarium material collected from the Bonkele River, D.R. Congo, and in the Kouilou River, Republic of the Congo. These samples were prepared for diatom analysis, examined using standard methods, and documented using both light and scanning electron microscopy. Key results – Several taxa belonging to the Eunotia asterionelloides complex were observed. Taxa from this complex are recorded in literature as either E. asterionelloides or E. zasuminensis. The taxon from fishponds in the D.R. Congo was identified as E. tukanorum, previously described from Brazil. The structure of the valve outline and raphe appear similar, particularly the raphe position and length. A second species was found on aquatic macrophyte (Utricularia and Nymphaea) herbarium specimens from the D.R. Congo and a third species from the Kouilou River in the Republic of the Congo. These latter two taxa superficially resemble E. zasuminensis. Although similar in valve outline, the taxa differ morphologically. The shape of the apices in larger cells is indented to a larger degree, and the raphe differs in its structure, particularly the shape of the terminal endings. The structure and position of the rimoportula also differ. Also, one of these taxa is sometimes strongly flexed around the apical axis. Based on morphology, we consider these taxa distinct from E. zasuminensis and from each other, and thus describe Eunotia globicephala sp. nov. and Eunotia magnaparva sp. nov.