Cosmarium rostafinskii Gutwiński, 1890

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 : 120-121

Cosmarium rostafinskii Gutwiński (Figs. 1, 8, 19)

At one location (loc. 3) a desmid was found that resembles very closely Cosmarium rostafinskii , as described by Gutwiński (1890: 67) from a gypsum funnel on a church in the west of present Ukraine. In a later publication Gutwiński (1892: pl. 1: 15) gave an illustration and a slightly different diagnosis. There are some small differences between his diagnoses and the shape of our specimens. Gutwiński mentions 4–5 crenations on each side (plus 4 at the apex) whereas, as a rule, we counted 6 crenations (however, sometimes on one or both lateral sides a crenation was missing). Counting the exact amount of the crenations under the light microscope is difficult, because the crenation closest to the basal corner is often hard to distinguish from the basal corner itself and sometimes crenations are aligned so close together that they look like a single one. This is certainly the case with the two large apical crenations at the corner of the apex. On our SEM-image (Fig. 19) it can be seen that they are associated with two closely aligned rows of granules that merge to one row towards the center of the semicell. It can also be observed that the crenations become gradually broader from the basis to the apical corner of the semicell. Only the two median apical crenations are distinctly smaller and this feature, together with the different shape of the apical crenations, renders the apex a truncate appearance. In Gutwiński’s original diagnosis, 8 rows of granules just above the isthmus are mentioned; while in his accompanying illustration something like ribs (costae) are drawn. Our SEM-images reveal that both descriptions are true. Every row consists of about three granules that are connected to each other to form a kind of ridge. Outline and general size agree very well with our specimens, so we are convinced that our specimens fit within the concept of Gutwiński.

West & West (1908: 251, pl. 89: 8–10) made C. rostafinskii a variety of C. speciosum P. Lundell (1871) . They illustrated three specimens. One (pl. 89: 8) is a copy of the illustration by Gutwiński and the other two are probably of their own. These latter illustrations differ somewhat from that of Gutwiński. The rows of granules just above the isthmus are depicted as separated granules instead of costae (see our discussion above), but the amount of crenations at the lateral margins agrees better with our observations. Also the size and general outline of the illustrations by West & West fit very well with our observations and that of Gutwiński. We disagree, however, with the decision of West & West to render it a variety of C. speciosum Lundell. As differentiating characteristics with respect to C. speciosum, West & West mention a more regularly pyramidate outline and a more evidently truncate apex. Next to those differences, however, cells of C. speciosum as originally described by Lundell (1871: 34, pl. 3: 5) compared with those of C. rostafinskii are larger (54–62 × 39–41 μm versus 46 × 31 μm in our fig. 1), concomitant with a larger number of marginal crenations and concentric series of submarginal granules, whereas also the supraisthmial costae are stronger developed.

Rather than with C. speciosum , C. rostafinskii could be confused with C. basiornatum (Grönblad) Coesel originally described as C. davidsonii var. basiornatum Grönblad (1926: 16) . Semicells of that latter species, however, differ in having an even more truncate, broader apex and about straight lateral sides ( Grönblad 1926, Coesel 1998). In several publications ( Skuja 1928: 172, Messikommer 1928: 206, Grönblad 1936: 9, Šťastný & Kouwets 2012: 301) the similarity of these two taxa is discussed, but in our opinion C. rostafinskii is well separated from both C. speciosum and C. basiornatum .

C. rostafinskii was only found at location 3, but in large numbers.

FIGURES 1–7. 1. Cosmarium rostafinskii . 2. C. benedictum . 3. C. notabile . 4. C. amstelodamense . 5. C. galeatum . 6. C. fruticosum . 7. C. scutiforme . Scalebar = 25μm.