Phylum Chlorophyta; sub-phylum Chlorophyceae; Order Zygnematales

There are two groups of Desmids: the "Placoderm" and the "Saccoderm" Desmids.

Placoderm desmids have cells composed of two halves (semicells), often almost divided from each other by deep median incisions. The cells are symmetrical about 3 planes, and often bear elaborate ornamentation. Genera are Cosmarium, Cosmocladium, Euastrum, Micrasterias, Staurastrum, Staurodesmus, Xanthidium.

Saccoderm desmids are simple shapes, cylindrical or spindle-shaped, rarely with any median constriction. This group forms the family Mesotaeniaceae and includes the genera Cylindrocystis, Mesotaenium, Netrium, Roya, Spirotaenia, Tortitaenia, and, in the suborder Closteriinae, Closterium, Gonatozygon and Penium, and in the suborder Desmidiinae, Actinotaenium.

Cosmarium	Cosmocladium	Euastrum	Micrasterias	Staurastrum	Staurodesmus	Xanthidium
Saccoderm:	Closteriinae		Mesotaeniaceae		Desmidiinae

ILLUSTRATIONS:

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Placoderm

	EUASTRUM	Cell composed of 2 symmetrical semicells with relatively flat aspect in face view (apical view elliptical). Cells generally have an apical notch and are more deeply incised around the margin.
		Euastrum ansatum
		Euastrum bidentatum
		Euastrum crassum
		Euastrum denticulatum
		Euastrum didelta
		Euastrum dubium
		Euastrum elegans
		Euastrum inerme
		Euastrum insulare
		Euastrum insigne
		Euastrum oblongum
		Euastrum pectinatum
		Euastrum pinnatum
		Euastrum verrucosum

Cosmarium	Cosmocladium	Euastrum	Micrasterias	Staurastrum	Staurodesmus	Xanthidium
Saccoderm:	Closteriinae		Mesotaeniaceae		Desmidiinae

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John Kinross