Phylum: Charophyta   Family: Desmidiaceae

Euastrum crassum var. microcephalum W. Krieger 1937

First described by Krieger (1937: 512, pl. 65: 6). It’s similar to the nominate variety but with a less pronounced pore surface and with four large and deep scrobiculae. Krieger (l.c.) notes: Slightly slimmer than the type, more than twice as long broad. Apex part of the semicell smaller, evenly distributed very long basal part.
Krieger’s cell dimensions: L: 100-230 µm; B: 45-80 µm; Is: 16-30 µm; Apex: 25-62.5 µm. (That’s a huge size-range just for the apex: probably a typing or printing error).
Found in moorland pools and bogs. Fairly common but not always possible to determine this variety from the nominate.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Krieger, W. (1937). Die Desmidiaceen Europas mit Berücksichtigung der aussereuropäischen Arten.
Ruzicka, J. (1977). Die Desmidiaceen Mitteleuropas, Volume 1, Part 2.