A comparative study of Cocconeis scutellum Ehrenberg and its varieties (Bacillariophyta)

Abstract We present an ultrastructure-based revision (using light and electron microscopy) of the type species of the genus Cocconeis, C. scutellum var. scutellum, and four often-mentioned but poorly described, morphologically related varieties: C. scutellum var. baldjikiana, C. scutellum var. clinoraphis, C. scutellum var. parva, C. scutellum var. posidoniae. In addition, we introduce three new taxa, C. scutellum var. gorensis var. nov., C. scutellum var. posidoniae f. decussata f. nov. and C. scutellum var. sullivanensis var. nov. The taxonomic relationships between these varieties and the remaining validly described C. scutellum varieties are analyzed on the basis of their ultrastructural differences. We also provide additional information on the geographical distribution of all analyzed C. scutellum taxa.