Identity and phylogenetic placement of Spirogyra species (Zygnematophyceae, Charophyta) from California streams and elsewhere¹

Abstract

Diversity of the filamentous green algae in the genus Spirogyra (Zygnematophyceae) was investigated from more than 1,200 stream samples from California. We identified 12 species of Spirogyra not previously known for California (CA), including two species new to science, Spirogyra californica sp. nov. and Spirogyra juliana sp. nov. Environmental preferences of the Californian species are discussed in the light of their restricted distribution to stream habitats with contrasting nutrient levels. We also investigated the systematic relationships of Spirogyra species from several continents using the chloroplast-encoded genes ribulose-1,5-bisphosphate carboxylase/hydrogenase large subunit (rbcL) and the beta subunit of the ATP synthase (atpB). Californian species were positioned in most major clades of Spirogyra. The phylogeny of Spirogyra and its taxonomic implications are discussed, such as the benefits of combining structural and molecular data for more accurate and consistent species identification. Considerable infraspecific genetic variation of globally distributed Spirogyra species was observed across continental scales. This finding suggests that structurally similar species from distant regions may be genetically dissimilar and that Spirogyra may contain a large number of cryptic species. Correlating the morphological and genetic variation within the genus will be a major challenge for future researchers.

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

“…Similarly, up to three genotypes of Spirogyra were detected at a single site (Chen et al ., 2012; Stancheva et al . 2013), and sympatric occurrence of cryptic (or pseudocryptic) species has been described for other microalgal assemblages such as diatoms (Vanormelingen et al ., 2008) and desmids (Nemjová et al ., 2011). Nevertheless, it should be considered that our genotypes may not represent true ‘cryptic species’, because we could not use all distinguishing features due to the absence of zygospores.…”

“…Similarly, Stancheva et al . (2013) characterized, by morphological and molecular methods, 15 Spirogyra species from streams in California. In general, application of molecular methods in morphologically uniform protists usually reveals hidden diversity on various levels, depending on the selected marker(s) (e.g.…”

“…It has been repeatedly shown that morphology is not congruent with phylogeny (Gontcharov & Melkonian, 2005; Chen et al ., 2012; Stancheva et al . 2013). Currently, both Zygnema and Zygnemopsis genera belong to order Zygnematales and family Zygnemataceae (Guiry, 2013).…”

“…Therefore, we decided to test whether our genotypes could be discriminated based solely on their vegetative morphology, even though it is well known that the molecular diversity of filamentous Zygnematophyceae is far greater than indicated by the lack of morphological variation (Chen et al ., 2012). Despite being based on generative morphological features, traditional species description of filamentous Zygnematophyceae usually includes information on cell diameter, and particularly chloroplast features including shape, length of protrusions, globularity and compressed appearance (Kadlubowska, 1984; Stancheva et al ., 2012, 2013). …”

Some silkweeds (Zygnemataceae, Zygnemales, Charophyceae) from the Upper Murrumbidgee River catchment

“…With twelve or more already described taxa that could be included using morphology in an expanded S. maxima, it would serve little purpose to describe more until the genetics and physiology are better known. Stancheva et al (2013) have shown that there may be two groups of species in Spirogyra with large numbers of chloroplast ribbons per cell, and that species presently assigned to Sirogonium may be found in one of these groups.…”