Desmid of the month
September 2012

Heimansia species *

Heimansia (formerly accounted the genus Cosmocladium) forms branched, 3-dimensional colonies. As in Cosmocladium, Cosmarium-like cells are interconnected by thin, transparent strands. Contrary to Cosmocladium however, those strands do not consist of bundles of microfibrils secreted by isthmial cell wall pores, but of shed, primary cell walls (Coesel 1993). Although, unlike in Cosmocladium, the colony consistency is retained in formalin-fixed material, Heimansia species are but but seldom recorded. In the Netherlands, the latest find of H. pusilla was in the early 1990's.

* The only Heimansia species so far described is H. pusilla (Coesel 1993). The herewith depicted taxon differs from H. pusilla in that its semicells are furnished with a distinct central tubercle. Most likely it is identic to Cosmocladium tumidum Johnson, in which case that taxon is to be transferred to Heimansia (Gerrath 1970).

References:
Coesel, P.F.M., 1993. Taxonomic notes on Dutch desmids II. — Cryptogamie, Algologie 14: 105-114.
Gerrath, J.F., 1970. Ultrastructure of the connecting strands in Cosmocladium saxonicum de Bary (Desmidiaceae) and a discussion of the taxonomy of the genus. — Phycologia 9: 209-215.