Mesotaeniacea

DESMIDS

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:

Saccoderm:

Mesotaeniacea *Cylindrocystis*	Unicellular Saccoderm Desmid: cells short, cylindrical with rounded ends, with 2 stellate chloroplasts

*Mesotaenium*	Saccoderm desmid with a single chloroplast
	This example has 4 longitudinal ridges, which is not reported in FAFBI. The cells were found in dense mucilage adhering to moss on a greenhouse roof
Netrium	Unicellular placoderm Desmid: cylindrical with tapering rounded ends, some slightly swollen in the middle, with 2 chloroplasts. (N. interruptum has each chloroplast almost divided in 2)

	Netrium digitus
	Netrium interruptum

*Roya*	Saccoderm desmid: elongated cylindrical cell with rounded ends, usually slightly bent . The single chloroplast has a notch in the middle .
	? Roya obtusa (this example is rather shorter than usual)
*Spirotaenia*	Unicellular Placoderm desmid : cylindrical cell with rounded ends and spiral band chloroplast

Tortitaenia	Saccoderm desmid: cylindrical, tapering at both ends (spindle-shaped). Chloroplast with spiral ridges (cf. Spirotaenia)
	Tortitaenia luetkemuelleri

Desmidiinae (suborder) : Actinotaenium
	Actinotaenium curtum

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*Cosmarium*	*Cosmocladium*	*Euastrum*	*Micrasterias*	*Staurastrum*	*Staurodesmus*	*Xanthidium*

Saccoderm:	Closteriinae		Mesotaeniaceae		Desmidiinae

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(back to desmid key)

John Kinross