Cosmarium notabile Brébisson

Geest, Alfred Van & Coesel, Peter, 2019, Some new and interesting desmids (Streptophyta, Desmidiales) from ephemeral puddles in the urban and industrial areas of Amsterdam (Netherlands), Phytotaxa 387 (2), pp. 119-128 : 123-124

Cosmarium notabile Brébisson (Figs. 3, 12, 13, 14, 21)

C. notabile described by De Brébisson (1856: 129) has turned out to be a highly problematic desmid taxon. Most of the taxonomic confusion was caused by De Bary (1858, pl. 6: 52–54) who, under the name of C. notabile , depicted an alga the cells of which have a higher length to breadth ratio and a much broader isthmus than those depicted by De Brébisson (1856, pl. 1: 15). More exact: where length to breadth ratio in De Brébisson’s (1856) cells can be calculated to 1.31, that in De Bary’s (1858) cells results in 1.72. Cell isthmus to cell breadth ratio in De Bary appears to be 0.72 versus only 0.42 in De Brébisson. In our opinion, the cells depicted by De Bary (1858) with their very shallow, open sinus resemble those of C. benedictum rather than those of C. notabile . Part of the confusion about those two species may be explained by the rather poor quality of De Brébisson’s original figures of C. notabile . Taking a closer look at his figures a few series of coarse submarginal granules may be discerned that he does not explicitly mention in his diagnosis. Those series of granules are completely missing in De Bary’s figures. Unfortunately, De Bary’s (1858) concept of C. notabile was adopted by later authors; see e.g. the well-known floras by West & West (1908) and Krieger & Gerloff (1965).

FIGURES 19–24. 19. Cosmarium rostafinskii . 20. C. benedictum . 21. C. notabile . 22. C. amstelodamense . 23. C. fruticosum . 24. C. scutiforme . Scalebar = 10μm.

Comparing the original drawings of C. notabile by De Brébisson with pictures of a Cosmarium taxon found in some of our samples under discussion (especially our fig. 12 ), we note a number of similarities. Aside from a comparable cell size and shape, a few series of coarse submarginal granules may be discerned whereas, at least under the light microscope, no other cell wall ornamentation is visible. Only in some of our SEM pictures a very slight indication of supraisthmial costae is to be seen. In conclusion, we think that our figures represent the same taxon as described under the name of C. notabile by De Brébisson (1856). For that matter, the cells in our material attributed to C. notabile , mainly collected at location 3, are rather variable in their length to breadth ratio, ranging from 1.32 to 1.50. Nevertheless, they were readily to be distinguished from the above-discussed C. benedictum .

Krieger & Gerloff (1965: 210) made C. benedictum a variety of C. notabile , but wrongly based their description of C. notabile on the concept of that species by De Bary (1858), see above. For that matter, it was Croasdale (in Prescott et al. 1981: 173) who emphasized the difference in concept of C. notabile between De Brébisson (1856) and De Bary (1858). She rightly recognizes the need of a new name for the many smooth-walled forms figuring in desmid literature under the name of C. notabile and newly describes C. levinotabile to meet that need. Unfortunately, as holotype of that species she gives the figures 6: 1–5 of C. notabile in De Bary (must be 6: 52–54) and as iconotypes figures 198: 1–5 in Prescott et al. (1981) representing both the drawings of C. notabile in De Bary and drawings of C. notabile in the flora by West & West (1908), in our opinion representing distinctly different species. Consequently, Croasdale’s description of C. levinotabile should be considered invalid.

Figures

FIGURES 12–18. 12–14. Cosmarium notabile. 15–16. C. galeatum. 17. C. fruticosum. 18. C. scutiforme. Scalebar = 10μm.