Phylogeny and classification of Zygnematophyceae (Streptophyta): current state of affairs.

Abstract

Conjugates (Zygnematophyceae) represent the most species-rich (ca. 4000 spp) algal lineage within the Streptophyta. Studies using various molecular markers have placed the class as one of the crown groups in Streptophyta and even suggested a close relationship between the zygnematophycean algae and land plants. Phenotypic diversity complicates systematics of the class and the relationships between its taxa remain poorly understood. Molecular phylogenetic analyses have established a number of clades in the class and revealed a disagreement between the traditional taxonomic structure of Zygnematophyceae and the pattern of phylogenetic relationships between the class members. in this paper, an overview of recent advances in our understanding of the phylogeny and classification of conjugating green algae is presented, with emphasis on the major clades established in the class, the clades' structure and polyphyly of some genera. We describe the areas of conflict and agreement between molecular phylogeny and traditional morphology-based taxonomy and stress that phenotypic characters provide little evidence for inferring relationships between taxa even at low taxonomic levels.

Molecular and morphological diversity of Zygnema and Zygnemopsis (Zygnematophyceae, Streptophyta) from Svalbard (High Arctic)

“…Currently, both Zygnema and Zygnemopsis genera belong to order Zygnematales and family Zygnemataceae (Guiry, 2013). Gontcharov (2008) mentioned 139 species of Zygnema , but 212 species are currently listed as taxonomically accepted in AlgaeBase (www.algaebase.org). Nevertheless, many were observed only once, making it highly probable that their ‘unique’ morphology reflects phenotypic plasticity, and that the number of species has been overestimated.…”

“…However, modern molecular phylogenetic studies repeatedly show that traditional taxonomy does not reflect the actual relationships, and reveal the existence of cryptic species (Gontcharov, 2008). For example, cryptic lineages that occur sympatrically across Europe were identified within the morphologically well-defined species Micrasterias truncata (Corda) ex Bréb (Nemjová et al ., 2011).…”

Diversity and morphological disparity of desmid assemblages in Central European peatlands

“…6). While we know that most of these genera are, in fact, polyphyletic or paraphyletic (Gontcharov, 2008;Hall et al 2008), the similarity of their disparity or complexity is not surprising, given the fact that they have been defined almost entirely on the basis of morphological data. Members of the genus Micrasterias generally had the highest partial morphological disparities (PD), indicating their large contribution to the total morphological disparity of the entire set ( Fig.…”

“…However, his study also incorporated the mesotaeniacean species that, as we now know from molecular data (e.g. Gontcharov, 2008), neither belong to, nor form a monophyletic group with, Desmidiales. While the 'flagship' species with the highest complexity values (as Micrasterias species), occurred typically in localities with average or higher pH, some reasonably complex taxa (as e.g.…”

“…The Desmidiales were chosen as a species-rich monophyletic group of green algae (Gontcharov, 2008;Hall et al, 2008), typically inhabiting benthic freshwater environments (Coesel & Meesters, 2007). Natural assemblages of desmids are known to subtly reflect the environmental conditions of localities (e.g.…”