Bijdragen tot de kennis der Nederlandse Desmidiaceeënflora 4. De leemputten bij Staverden

Near Staverden (province of Gelderland) there is a moist heath where a calcareous loam is found mostly very close to the surface. In the past the loam was exploited in several places, which resulted in an unevenness of the terrain and in a number of gradients (wet-dry, rich in humus — poor in humus, lime-rich — poor in lime). The more or less permanently waterfilled loam pits contain a rich desmid flora characteristic of a mesotrophic environment. Among the taxa recorded from this locality four are new for the Netherlands, viz., Staurastrum sexcostatum var. productum, Cosmarium annulatum, C. decedens var. apertum, and C. notabile. Of common occurrence in more oligotrophic shallow depressions filled with Sphagnum found at other sites in the area are, e.g., Staurastrum arnellii and its var. spiniferum. We agree with MESSIKOMMER (1929) in doubting whether these two taxa indeed represent one species. The ‘typical’ variety of S. arnellii may well belong in the affinity of S. muricatum and S. hirsutum, whereas the var. spiniferum rather belongs near S. scabrum.