Molecular phylogenetics coupled with morphological analyses of Arctic and Antarctic strains place Chamaepinnularia (Bacillariophyta) within the Sellaphoraceae

Abstract

The diatom genus <i>Chamaepinnularia</i> was first published by Lange-Bertalot et Krammer in 1996 to accommodate several small species previously included within <i>Navicula</i> and <i>Pinnularia</i>. Despite its morphological similarity to those two genera, the family-level classification of <i>Chamaepinnularia</i> has been considered <i>incertae sedis</i> since its description almost three decades ago. We provide the first molecular characterisation (18S and rbcL) of the genus based on cultured polar strains and investigated its phylogenetic placement. Molecular data are complemented with observations on living cells, as well as detailed examination of oxidized material with light microscopy and scanning electron microscopy. The 12 investigated strains were morphologically identified as three taxa: two already described species (<i>C. gerlachei</i>, <i>C. krookii</i>) and one here newly described (<i>C. australis </i>sp. nov.). These species formed three separate, well-supported branches in the phylogeny. Our analyses placed <i>Chamaepinnularia</i> as a sister group to members of the Sellaphoraceae for which sequence data exist (i.e. <i>Sellaphora</i>, <i>Fallacia</i>, <i>Rossia</i> and <i>Diprora</i>). Based on the presence of hymenate areolae, a single H-shaped plastid with girdle appressed plates and the results of the phylogenetic trees, we propose the inclusion of <i>Chamaepinnularia</i> within the family Sellaphoraceae, which altogether form a supported monophyletic group.