Staurodesmus convergens
(Ehrenberg ex Ralfs) S.Lillieroth, 1950
Most likely ID: n.a.
Synonym: Arthrodesmus convergens, Staurastrum convergens
Sampling location: Holzöstersee (Austria), Schwemm Moor (Austria)
Phylogenetic tree: Staurodesmus convergens
Diagnosis:
- cells biradial
- semi-cells elongated elliptical
- apices convex
- each semi-cell with two spines, can be reduced
- spines directed towards the equatorial plane
- length 35–55 µm, width 50–85 µm
- cell wall finely granulated
- chloroplasts with each one pyrenoid
So far, I have only found Staurodesmus convergens at sites in Austria. In the samples from the Schwemm Moor it was scattered but regularly present.
The species is very easy to recognize by the equatorially curved spines on the lateral edges of the semi-cells. These can vary greatly in length and shape, which is why Lenzenweger (1997) considers the differentiation of varieties to be of little use. In my population, the specimens corresponded closely to Lenzenweger’s drawing (see above).
Fig. 1 a-b: Staurodesmus convergens. L = 47 µm. Two focal planes of a specimen found in the Schwemm Moor. Obj. 100 X.