A morphology-based phylogeny of the diatoms formerly assigned to the Orthoseiraceae (Bacillariophyta): phylogenetic relationships, character analysis and classification

Abstract

ABSTRACT A formal cladistic analysis of the morphological features of taxa assigned to the Orthoseiraceae, including Phycavernosa, Guarreraea and species of the genus Orthoseira is developed for 35 taxa based on 16 characters along with two Melosira species and four biddulphioid species as ingroup taxa as well as Leptocylindrus danicus as the outgroup. A consensus tree of 266 843 most parsimonious topologies suggests that the Orthoseiraceae is monophyletic, and that Guarreraea plus all former species of Orthoseira represent a monophyletic group. This analysis of morphological data did not provide support for the members of the Orthoseiraceae being more closely related to melosiroid or biddulphioid diatoms. Relationships within the monophyletic orthoseiracean group are detailed. Due to the exclusion of the generitype of Orthoseira not possessing carinoportulae which are central tube processes, one of the diagnostic features of the former Orthoseiraceae, other taxon names are described and recognized herein. We recognize and describe a new order, the Liparogyrales, based on the genus Liparogyra for taxa that were previously assigned to Orthoseira. Two families, the Phycavernosaceae, comprising the genus Phycavernosa, and the Liparogyraceae, comprising Guarreraea and taxa formerly assigned to Orthoseira, are described. The genus Liparogyra is composed of three subgenera: the subgenus Liparogyra, the subgenus Porocyclia, and the subgenus Insularis which are diagnosed by synapomorphic features. Based on our analysis, the genus Stephanosira appears to lack synapomorphies. Liparogyra, Porocyclia and Stephanosira had previously been described as genera by Ehrenberg. Guarreraea and one newly proposed genus are also included in the Liparogyraceae. Several other lineages are aphyletic, due to them either being monotypic or without diagnostic features. Thus, a total of 29 species in five genera are recognized within the newly described order and two newly described families. Eighteen new combinations are proposed for the transfer of taxa from Orthoseira to other genera. Homoplasy amongst some of the character states is discussed.