Taraxacum frisicum Soest (syn. Taraxacum apiculatum Soest) op het vasteland van Friesland

Taraxacum frisicum belongs to the section Palustria, a group of species that prefer natural and semi-naturalsites which are periodically flooded. In the Netherlands, T. frisicum is only known from the Province of Friesland. Formerly,the plant used to be abundant in nutrient-poor fen meadows of the ‘Lage Midden’ area. In the early 1990s, T. frisicumwas no longer found at the old sites despite targeted searches. It seemed ‒ at least on the mainland of the province ‒to be extinct. The species was found only in small numbers on the Frisian island of Terschelling. In Dutch literature, T.frisicum is known as a species with a very small distribution area which is only sporadically found outside Friesland. However, comparative culture experiments of T. frisicum and T. apiculatum in Germany (Karlsruhe) showed that the two species are morphologically indistinguishable. This means that the distribution area of T. frisicum is not limited tothe Province of Friesland in the Netherlands, but includes some areas in Germany (Thuringia and Bavaria) as well. On the Frisian mainland, Taraxacum frisicum has been found recently along the IJsselmeer coast. In the spring of2020 and 2021, data were collected about its habitat at three locations: ― In the ‘Bocht van Molkwerum’, an area outside the IJsselmeer dyke between Hindeloopen and Molkwerum, a small population of Taraxacum frisicum is present. At this site, T. frisicum grows together with T. palustre and T.lucidum in a grassland with a floristic composition that corresponds to the Calthion palustris (Molinietalia). A few diagnostic species of the Lolio-Potentillion anserinae and two species that are characteristic for desalinated soil (Pulicaria dysenterica, Oenanthe lachenalii) are also present. ― In the ‘Makkumerzuidwaard’, a rich population of Taraxacum frisicum was observed in a grassland outside the IJsselmeer dyke. The vegetation shows similarities with that of the ‘Bocht van Molkwerum’ due to the coexistenceof species of the Molinio-Arrhenatheretea and the Lolio-Potentillion anserinae, while a species that is characteristic of desalinated soil is also present (Pulicaria dysenterica). On the other hand, species that are characteristic of moderately nutrient-rich grasslands of the Calthion, the Molinietalia, and the Parvocaricetea are almost completely absent. Taraxacum frisicum appears to thrive surprisingly well in this nutrient-rich grassland. ― In the ‘Workumer Nieuwland’, an old polder inside the IJsselmeer dyke near Workum, Taraxacum frisicum grows in a gradient zone where acidophilic and basophilic plant species coexist. There, T. frisicum is part of a species-rich vegetation whose total floristic composition fits remarkably well with the Rhinantho-Orchidetum morionis (Calthion).Three other Palustria species are also present in the ‘Workumer Nieuwland’: Taraxacum anglicum, T. palustre andT. udum. At this location, which is rich in all kinds of gradients, ecological similarities and differences between the four Palustria species are clearly visible: a) T. frisicum and T. udum are both limited to the gradient zone itself, b) T. anglicum prefers a low-lying Calthion community in which some Convolvulo-Filipenduletea species occur, and c) T. palustre, the Palustria species with the widest ecological amplitude, occurs over a significant part of the terrain. In the second half of the last century, as a result of major changes in water management and the mowing regime, the area of the fen meadows of the ‘Lage Midden’ declined enormously. Taraxacum frisicum rapidly deteriorated as well and eventually, it could no longer be found at the old locations. The fact that Taraxacum frisicum is able to persist in a few places in the IJsselmeer coastal area is undoubtedly due to the favorable water management there. These populations are of great importance for the conservation of the species, especially since in Germany T. frisicum is threatened with extinction as well.