Desmid of the month
January 2019

Cosmarium nasutum

Cosmarium nasutum is a characteristic species, readily to be recognized by its regularly, deeply crenate cell outline. In frontal view, semicells are trapeziform-semicircular with eight bipapillate, marginal crenations. Just above the isthmus there is a big emarginate wart, often accompanied by one or two short, transversal rows of smaller granules immediately above it. This supraisthmial ornamentation is separated from radiate series of intramarginal granules by an unsculptured zone. Zygospores are globose and furnished with spines that are bi- or trifurcate at the extremity and have a ring of teeth at the upper side of their conical base. C. nasutum has a predominantly arctic-alpine distribution. In the Netherlands it is only known from a few sites, on one of them it was found with zygospores.