Phylogeny and systematics of Pseudodictyosphaerium, Mychonastes and related coccoid green algae (Chlorophyceae)

• Published in: Journal of phycology Vol. 39; no. S1; p. 16
• Main Authors: Fawley, M W, Fawley, K P, Buchheim, JA, Buchheim, MA
• Format: Journal Article
• Language: English
• Published: 01.06.2003
• Subjects: Chlorophyceae; Chlorophyta; Freshwater; Korshpalmella; Mychonastes; Pseudodictyosphaerium; USA, North Dakota, Arrowwood Natl. Wildl. Refuge; USA, Minnesota, Itasca State Park
• ISSN: 0022-3646
• DOI: 10.1111/j.0022-3646.2003.03906001_45.x

Species of Mychonastes, Pseudodictyosphaerium, and Korshpalmella all have spherical (or nearly so) coccoid cells without pyrenoids. Mychonastes and Pseudodictyosphaerium are apparently frequent components of the picoplankton of lakes, although they had not been reported from North America prior to our studies. We have examined several isolates of Mychonastes, Pseudodictyosphaerium, and Korshpalmella from lakes and ponds in Itasca State Park, Minnesota (USA) and Arrowwood National Wildlife Refuge, North Dakota (USA). These isolates comprise 5 different 18S rDNA sequence types, none of which have a sequence identical to any published sequence for Mychonastes or Pseudodictyosphaerium. Four of these 18S types produce solitary cells, consistent with Mychonastes spp. However, other isolates all have identical 18S rDNA sequences, but are either unicellular, colonial with connecting stalks, or colonial in an amorphous matrix, consistent with Mychonastes spp., Pseudodictyosphaerium spp. or Korshpalmella spp, respectively. For some isolates, the colonial character is plastic, with different morphologies seen with different growth conditions. Ribosomal ITS and rbcL sequences also indicate little or no diversity among the isolates with various morphologies. These results suggest that the colonial habit is not a reliable generic character. Phylogenetic analyses of both rbcL and 18S rDNA sequences indicate that Mychonastes and Pseudodictyosphaerium spp. are a distinct lineage within the Chlorophyceae and should be placed in a new family.