STEPHANODISCUS NEOASTRAEA AND STEPHANODISCUS HETEROSTYLUS (BACILLARIOPHYTA) ARE ONE AND THE SAME SPECIES

Abstract

Stephanodiscus neoastraea Håkansson et Hickel is distinguished from S. heterostylus Håkansson et Meyer by the absence of valve face fultoportulae. Scanning electron microscopy analyses (SEM) revealed, that cultures established from a single cell of S. neoastraea and/or S. heterostylus persistently contained a mixture' of cells with and without valve face fultoportulae. Amplification of the ITS2 spacer region of the nuclear encoded rRNA transcription unit yielded a single band in an agarose gel electrophoresis for three “mixed” cultures tested. Furthermore, sequencing of the ITS2 region resulted in unambiguous sequences that were identical for each strain investigated. Ambiguous peaks which may originate from sequencing a mixture of different templates did not appear in the electropherogram. Thus, no, one or several valve face fultoportulae appear in the same species. Absence or presence of fultoportulae is not a useful character for differentiating S. neoastraea and S. heterostylus. Presence or absence of tubular processes on the valve face is a variable character, clearly expressed in clonal culture, and thus cannot be used for species discrimination. The species name S. heterostylus is a “nomen nudum”, and thus invalid.