Staurastrum brachiatoides Coesel et Van Westen, 2014

Staurastrum brachiatoides Coesel et Van Westen , spec. nov. ( Figs. 2–7 View FIGURES 1–7 , 26, 27 View FIGURES 22–29 )

Cells in frontal view about as long as broad, deeply constricted. Sinus widely open, more or less rectangular. Semicells 3- angular in outline. Semicell body gradually passing into robust, diverging arm-like processes that are 2–4-furcate at the end. Cells in apical view 3-radiate. Cell wall smooth. Zygospores irregularly elongate with broadly rounded angles. Dimensions: length of the cell body (without processes) (9–)11–15(–17) µm, isthmus breadth 7.0– 8.5 µm. The mature zygospore measures 23–27 × 13–16 µm.

Type:— THE NETHERLANDS. Drenthe: Borger, Meindersveen , 52.936° N, 6.728° E, pH 4.6, conductivity 60 µS cm -1, Van Westen, 29 August 2009 (holotype L! Hugo de Vries Lab 2013.02, preserved as a fixed natural sample) GoogleMaps .

Differential diagnosis: —As the name of the newly described species indicates, it resembles Staurastrum brachiatum Ralfs (1848: 131) . The latter species is known to be highly polymorphic. Presumably, a number of different formae and varieties described under that species name represent species of their own ( Coesel & Meesters 2013). In our Drenthe investigation several morphotypes could be distinguished, differing in cell size and markedness of the furcate ends of the processes. One of these types, characterized by relatively large cells and spiny zygospores, obviously is identic with Staurastrum brachiatum as originally described in Ralfs (1848), ( Figs. 28, 29 View FIGURES 22–29 ). A second type, consistently smaller in cell size and with less pronounced furcate ends ( Figs. 2, 3, 4 View FIGURES 1–7 , 26 View FIGURES 22–29 ) appeared also to differ in the shape of its zygospore. Instead of a quadrate spore furnished with a number of stout spines as in St. brachiatum , the zygospore of our species under discussion is more elongate with broadly rounded angles lacking any trace of spines ( Figs. 5, 6, 7 View FIGURES 1–7 , 27 View FIGURES 22–29 ). Particularly this deviating type of zygospore led us to describe this alga as a new species. Application of the t-test to differences in cell length (apex to apex) showed a significant difference (p <0.001) between both species ( Fig. 30 View FIGURE 30 ).

Ecology: —In the province of Drenthe, St. brachiatoides appears to be much more widely distributed than St. brachiatum . Staurastrum brachiatum was found in only three areas in the province of Drenthe. Surprisingly, all locations were shallow oligotrophic to mesotrophic pools on former agricultural land with pH values between 5.0 and 6.5. Staurastrum brachiatoides is very common in acidic oligotrophic moorland pools with pH 4.0–5.5. Application of the t-test to differences in the pH of 14 locations showed a significant difference (p <0.002) between both species ( Fig. 31 View FIGURE 31 ).

In the meantime, sporulating St. brachiatoides is also known from several sites in the Dutch province of Noord-Brabant and most likely, judging from vegetative cell characteristics (dimensions), in the Netherlands St. brachiatoides is much more common than St. brachiatum .