A comparative study of the germination ecology of some microspecies of Taraxacum Wigg.

Of the large genus Taraxacum Wigg. about 200 agamospermous (micro-)species occur in the Netherlands. The maintenance of this opulence of taxa is presumably attributable to ecological factors. In order to obtain a better insight, experiments were carried out to determine the effect of temperature and light on the germination and the possible changes after a period of storage. Eleven micro-species were comparatively studied. Appreciable differences between species were recorded; the optimum germination temperature varies from 10°C to 30°C; in some species the germination process is stenothermic and in other ones it is eurythermic. Also the dependance upon light for germination differs. Storage outside of the seed bank did not change the germination pattern of the various species to a great extent, nor did it change the mortality per unit of time appreciably. Within the seed bank the temperature dependence decreases whereas the light dependence increases, and the mortality appears to be related to the time of the year. The various germination strategies seem to be adaptations to the respective habitats on the one hand (dune dandelions, for instance, only germinate at low soil temperatures), and on the other hand they seem to be correlated with inter-specific niche differentiation (e.g., when of two sympatric species the one has a germination optimum at 10°C, and the other one at 20°C). The results of the present inquiry strongly suggest that in the Netherlands an ecological differentiation is of common occurrence among microspecies of Taraxacum, and apparently plays an important part in the maintenance of the taxonomic diversity within the genus.