Original paper
Kritische Wertung der Taxa in Didymosphenia (Bacillariophyceae)
[Critical appraisal of the taxa in Didymosphenia (Bacillariophyceae)]
Metzeltin, D.; Lange-Bertalot, H.
Nova Hedwigia Band 60 Heft 3-4 (1995), p. 381 - 405
21 references
published: Jun 20, 1995
DOI: 10.1127/nova.hedwigia/60/1995/381
ArtNo. ESP050006003002, Price: 29.00 €
Abstract
Didymosphenia populations originating from localities in Siberia/Russia (Lake Baikal, River Angara), Pakistan (Himalaya, 3300 m above sea level), Ireland (Killarney) and from the Faroe Islands have been investigated in LM and SEM. Other populations from Norway, Sweden, Finland, Scotland, Russia (Lake Onega, Lake Issyk), Kazakhstan (River IIi), and Svalbard we compared in LM only. We distinguish 5 taxa at the specific rank. 1.) Didymosphenia geminata (Lyngb.) M. Schmidt with three, provisionally designated morphotypes: geminata sensu strictu, capitata and subcapitata. 2.) Didymosphenia siberica (Grun.) M. Schmidt (sensu strictu). 3.) Didymosphenia curvata (Skv. & Meyer) nov. stat. 4.) Didymosphenia clavaherculis (Ehr.) nov. comb. 5. ) Didymosphenia pumila nov. spec. These taxa are differentiated by the structure of the areolae which is profoundly different in D. geminata and D. clavaherculis compared to D. siberica, D. curvata, D. pumila. Nevertheless we do not intend to split the genus on this criterion, despite several recent cases of hasty splittings by other authors. Our observations are compared with older and more recent literature data, in particular with the numerous infraspecific taxa introduced by Skvortzow & Meyer (1928) and Skvortzow (1937). The taxa created by the latter authors cannot be distinguished from each other. Moreover they do not represent real populations. From the critical biological view of modern taxonomy they should be seen as typologically described “pseudo-taxa” only. Of course authors always select and name single individuals as regular variants of the cell cycle. However, their studies on Lake Baikal did not reveal the 5 real species that occur in 6 to 7 populations, when one takes the morphotypes (populations) into account. Despite these obvious shortcomings one of these taxa, D. geminata var. baicalensis fo. curvata is chosen as the basionym for a new species: D. curvata. It is shown that Didymosphenia dentata Dorogostaisky sensu Skvortzow & Meyer should not be regarded as a distinct species or race. It is evidently based on an optical artefact. Under a certain focus the high profile of the transapical costae of D. geminata resemble a regular row of spines at the junction of the valve face and mantle. Two forms of spines occur in subapical positions. Continuous spines occur in more weakly silicified marginal crests in D. geminata and D. clavaherculis. In the other three species however, completely isolated, more solid and longer spines occur on the edge of the mantle, without any traces of crests. Apparently they were overlooked (corroded?) by Dawson (1973b).
Keywords
Siberia • Russia • Kazakhstan • Svalbard • morphotype • specific rank • intraspecific taxa