Phylogeny and characterization of Paraeustigmatos columelliferus, gen. et sp. nov., a member of the Eustigmatophyceae that may represent a basal group within the Eustigmatales

The new taxon, Paraeustigmatos columelliferus, was isolated from a mat of the filamentous alga Zygnema on the shore of Lake Monticello in Arkansas, USA. The results of the phylogenetic analysis of 18S rDNA and rbcL sequence data suggest that this alga is likely allied with the Eustigmatales; alternately, it may represent a new third linage of the class. Light and electron microscopy reveal cellular features similar to other members of the Eustigmatophyceae; however, the cell wall bears unusual structures that resemble the columellae of the walls of pollen grains.