The taxonomy ofUlva(Chlorophyceae) in the Netherlands

Open Access
Publisher Website
Google Scholar
Abstract
On the basis of 160 living samples from 26 different stations five Ulva species were distinguished, and described for the Netherlands coast, namely U. pseudocurvata nov. spec., U. curvata (Kütz.) De Toni, U. lactuca L., U. rigida C.Ag. and U. scandinavica Bliding. Unialgal cultures were isolated from these samples in order to test the validity of the taxonomic criteria and to test the growth response of germlings and young blades to varying salinities. The following criteria appeared to be taxonomically valid, though most of them are subject to wide variation: (1) macroscopic morphology (including colour and texture); (2) form and arrangement of the cells in surface view; (3) the structure of the basal region (form and size of rhizoidal cells; the presence or absence of small-celled marginal wings; the presence or absence of longitudinal rhizoidal ribs; and the presence or absence of a flat central cavity in the lower basal region and the stipe); (4) the number of pyrenoids in a vegetative cell; (5) the appearance of the chloroplast in surface view; (6) the size of the cells; (7) the height-to-width ratio of the cells in cross-section; (8) thallus-thickness; (9) the morphology of young germlings; (10) the mode of reproduction. The results of this study largely confirm the taxonomic concepts of Bliding in Ulva. Diversity in Dutch Ulva appears to be greater than previously supposed. The five Ulva species have different distributions with regard to the estuarine gradients. Only U. lactuca and U. pseudocurvata grow attached to wave-exposed sea dikes and harbour moles of open coasts, but they also occur in more sheltered euhaline to polyhaline tidal waters. U. curvata, U. scandinavica and U. rigida are common in polyhaline man-made lakes in the south-western Netherlands, but also occur in tidal waters growing attached to shells and stones embedded in tidal sand- and mudflats. The latter three species were not found on open sea-coasts. Good growth of germlings and young blades occurs in a wide range of salinity (mainly 17–34%. S) and does not show a distinct correlation with differences in distribution in nature