Cytological and ecological notes on the Taraxacum sections Erythrosperma and Obliqua of the coastal area of the Netherlands

In this first publication of a series reporting on the results of a biotaxonomic and ecological research project concerning the genus Taraxacum, cytological and some oecological data are recorded of 13 species belonging to the sections Eryihrosperma and Obliqua from the dune area of the province of N. Holland and from the North Sea island ofTerschelling (The Netherlands), are recorded. I n most of the population samples from 4 to 8 different species were found. The populations from the mainland proved to be richer in species than those of Terschelling. Some ecological and possible genetic implications of the sympatric occurrence of so many species in the same habitat are discussed. The chromosome numbers of T. commixtum (2n = 24,32) and of T. laetiforme (2n = 24) had not previously been determined. I n four other species chromosome numbers were found which differ from counts of the same species as reported in the literature. Both the local and the regional karyological variation are appreciable. There is a remarkable concentration of (newly recorded) tetraploid forms in a restricted area within the mainland area studied. A study of the chromosome morphology revealed a most inconsistent pattern of satellites and secondary constrictions within a single species, involving both their number and their size or location. In the discussion some attention has been paid to the conceivably erroneous reports in the literature of hypertriploidy which may be attributable to this inconsistency of the chromosome morphology.