Seizoensveranderingen bij bladeren van Taraxacum

During a whole year several aspects of the seasonal variation in the leaves of four Taraxacum species were studied on the island of Schiermonnikoog. The species investigated are T. lacistophyllum T. commixtum, T. nordstedtii and T. limnanthes. The vegetation types in which the specimens studied occur are briefly described. The results for the first three species show a great deal of similarity. The plants have deeply incised leaves in spring. The degree of incision gradually decreases from May until September, when several specimens have leaves with completely entire margins. After September the degree of incision increases slowly, until the situation with deeply incised leaves is reached again in May. In T. limnanthes, a species which never has incised leaves, the leaf width respectively increases or diminishes in the same two periods. All four species show a decrease in the number of leaves from May until July, and after that an increase again. The average leaf length diminishes from May until March, after which it increases again, while a temporary increase sometimes was noticed in September. A number of specimens of T. lacistophyllum and T. commixtum remain underground (without leaves) for some time in summer. The time of appearance and degree of the changes in leaf shape, size and number differ to some extent within and between the species. In conclusion it may be stated that the rosettes of the Taraxacum species investigated consist of several long, deeply incised leaves in May and of only a few short, slightly or not incised leaves in summer and early autumn. The investigation has shown that size and shape of Taraxacum leaves found in summer in a vegetation, especially in dry dunes, give very little information about the identity of the Taraxacum species that are in fact present in this vegetation, and about their number.