Cytogeography of Taraxacum sectio Taraxacum and sectio Alpestria in France and adjacent parts of Italy and Switzerland, including some taxonomic remarks

In France and adjacent parts of Italy and Switzerland the distribution of diploid and triploid specimens of Taraxacum (mainly) sect. Taraxacum has been established on the basis of about 200 population samples and of herbarium specimens (c. 5,500 individuals in all). Most diagnoses are based on pollen characteristics, a minority on chromosome counts. Triploids are common throughout France. Diploids occur in the major part of the area with a relative frequency per population of 3 to 100%; they become more common southward from Le Mans-Tours-Strasbourg. Some data from the northern region suggest that there may be a broad transitional zone (towards total absence of diploids), reaching to Middle-Belgium and the Dutch South-Limburg area. To the south diploids are present in the Pyrenees and elsewhere in northern Spain, and in the Alps of Northern Italy. There are but weak indications pointing at some overall ecological differentiation between the diand triploid cytodemes. The presence of numerous diploid, sexual species came to light of which 26 belong to sect. Taraxacum and 2 to sect. Alpestria. Some of the species occur at both the ploidy levels. One may expect that more microspecies may prove to be diploid. In the discussion attention is paid to (1) some of the evolutionary mechanisms thought to be active in the sections studied (facultative sexuality, re-diploidisation) and (2) the consequences of the present data in respect of the applicability of the microtaxonomy within the range of the distribution of the sexual diploids.