Miscellaneous Notes on Scirpus Lacustris L. sensu Lat. in the Netherlands

In literature quite different opinions have been developed with regard to the species-concept of S. lacustris L. and S. tabernaemontani Gmel. In the nineteenth century several authors considered these species as modifications of S. lacustris L., owing to the resemblance, the unstable characteristics, the merging into one another under the influence of changing environmental conditions or the occurrence of intermediates. This does not exclude, however, the possibility that the unstable characteristics, the occurrence of intermediates and probably even the merging into one another should be ascribed to the growth of hybrids between the species mentioned above; from one locality this hybrid is on record. Consequently, in the twentieth century they are usually considered as separate species. An examination of the specimens occurring in the Netherlands showed, that in one locality in our country a highly fertile intermediate grows, with the same chromosome number as the other two forms, whilst the plants developing from the seeds of the intermediate are equal in morphological characteristics to those of the preceding generations. It follows that on no account the intermediate can be a hybrid. It is thought that the intermediate has been originated b} “introgressive hybridization” sensu Anderson and Hubricht (1938), which means in this case by crossing of S. lacustris L. and S. tabernaemontani Gmel. followed by back-crossings with the parents. Moreover, in some instances the possibility does seem to exist that between these species cross-breeds with undiminished fertility are yielded. It follows that in some localities in the Netherlands the boundaries between these species have been obliterated. According to these data the above-mentioned species are considered to belong to the same commiscuum sensu Danser (1950). On the strength of the fertility of the cross-breeds, the occurrence of gradation, the same chromosome numbers, the morphological resemblance and the fact that they reach their optimal development in different habitats, they are in this paper unitied into the same species. This means they are ecotypes (subspecies), respectively the ssp. lacustris and the ssp. glaucus (Smith) Hartman, of the ecospecies S. lacustris L. sensu lat. The intermediate has been described as the ssp flevensis of S. lacustris L. sensu lat.. which, in all probability, continues existence in the habitat of the ssp. lacustris as a consequence of the planting out by man. In the course of this examination data on the polymorphy, the distribution and the hybrids of S. lacustris L. sensu lat. X S. triqueter L. in the Netherlands have been obtained.