Ceramium diaphanum (Lightf.) Roth, its varieties and forms as found in the Netherlands

The genus Ceramium is one of the most difficult genera of the Algae. The species vary a great deal and, even when the differential characters are carefully chosen, still are connected by transitions. Moreover, there is a strong reticulate relationship within the genus, and henceforth there exists a great diversity of opinion regarding the limits of taxa of various ranks. The author is much indebted to the directors of the “Rijksherbarium” at Leiden, the Botanical Museum at Copenhagen, the “Universitets Botaniska Museum” at Lund, “Botaniska Museet” at Uppsala, as well as to Dr L. G. Sjostedt, who have rendered it possible to study a number of types, viz. of Kützing, Kylin, Petersen and Sjöstedt. Unfortunately, there was no possibility of studying the types of Ceramium diaphanum (Lightf.) Roth var. diaphanum, var. temissimum Roth * and f. corticatulo-strictum Kylin. It is to be regretted that Petersen failed to indicate type-specimens. The result is that the type-collections of his taxa are sometimes very extensive. The author is also much indebted to the directors of the “Rijksherbarium” at Leiden (L.), the “Zoölogisch Station” of the “Nederlandsche Dierkundige Vereeniging” at Den Helder (N.D.V.) and the herbaria of the Universities of Amsterdam (A.) and Utrecht (U.) for putting at his disposal their Netherlands’ material of Ceramium diaphanum (Lightf.) Roth. It is a great pleasure to the author to express his particular gratitude to Dr Josephine Th. Koster for her extensive assistance regarding this difficult investigation as well as to Dr R. A. Maas Geesteranus and Dr S. J. van Ooststroom for giving some nomenclatural advice. In the text most literature references are abbreviated; for full titles the bibliography at the end of the paper should be consulted.