Cosmarium grantii J.Roy & Bisset

Van Westen, Marien C. & Coesel, Peter F. M., 2021, Taxonomic notes on desmids from the Netherlands IV, with a description of another five new species, Phytotaxa 522 (3), pp. 240-248 : 243

Cosmarium grantii J.Roy & Bisset ( Figs 1 , 9, 10, 11 , 30 )

Cosmarium grantii was described by Roy (1893, pl. 1: 10) and Roy & Bisset (1894, p. 102) from from wet rocks in northeastern Scotland. Although this species was reproduced in the British flora by West & West (1912) those latter authors state it never to have seen themselves. As far as we could trace, no later records have been published either. So, it seems to be a decidedly rare species. Yet we think that an alternative explanation may be found in its close resemblance to the above discussed Cosmarium neocrenatum . C. grantii differs from that latter species by cells that are but slightly longer than broad, resulting in an almost quadrate cell shape. Quoting Roy & Bisset (1894: 102) cells are ‘nearly as broad as long’ [so not ‘almost as long as broad’ as stated in West & West (1912: 38)!] Cells of C. neocrenatum on the contrary, as depicted in the manuals mentioned, are distinctly longer than broad, resulting in a roughly rectangular cell shape. An additional differentiating feature may be found in the supraisthmial cell wall sculpture. Whereas that ornamentation in C. neocrenatum usually largely consists of a series of 3-6 longitudinal costae, in Roy & Bissets’ diagnosis (1894: 102) of C. grantii they mention ‘five pairs of prominent granules at the base of each semi-cell’, see also the corresponding picture in Roy (1893, pl. 1: 10). Considering the cells depicted in our figs 1, 11 and 30, those cells well meet the characteristics of C. grantii . A relevant additional differentiating feature regarding C. neocrenatum could be in their ecology. Whereas in the Netherlands C. neocrenatum is characteristic of slightly acidic to circumneutral substrates in fen hollows, C. grantii , as known from a number of sites in the province of Drenthe, was encountered on wet acidic substrates in moorland areas.

Figures

FIGURES 1–8. Drawings 1. Cosmarium grantii (from Eexterveld, province of Drenthe, the Netherlands). 2. C. palatiniforme. 3, 4. C. neonotabile (no 4 from Holmers, province of Drenthe, the Netherlands). 5. C. neocrenatum. 6. C. sphagnicola. 7. C. sphagnicoliforme (with zygospore). 8. C. regnesiforme.

FIGURES 9–17.LM photographs. 9–11. Cosmarium grantii (from Eexterveld). 12–14. C. neocrenatum (12 from Kiersche Wieden, province of Overijssel, the Netherlands, 13, 14 from type location). 15–17. C. neonotabile (16 from Holmers, 15,17 from type location). Scale bar = 10 µm

FIGURES 30–38. SEM photographs. 30. Cosmarium grantii (from Eexterveld). 31. C. neocrenatum (from Iceland). 32. C. neonotabile (from Holmers). 33. C. palatiniforme (from type location). 34. C. sphagnicola (from Eexterveld). 35. C. sphagnicoliforme (from type location). 36, 37. C. regnesiforme (from type location). 38. C. regnesi (Zeijen, province of Drenthe, the Netherlands). Figures 30–33: Scale bar = 10 µm, Figures 34–38: Scale bar = 5 µm