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| Vroman, M.; Ietswaart, J.H.. |
| Taraxacum limnanthes was described by HAGLUND (1946). VAN SOEST (1965) distinguishes two subspecies. One of these, subsp. limnanthoides, occurs in the Netherlands. In this country it is found on the Wadden Islands, near the IJssel Lake (the former Zuiderzee), and in Zeeland. The present paper is concerned with investigations on Schiermonnikoog (one of the Wadden Islands). Here T. limnanthes subsp. limnanthoides occurs in an area with a west to east salt gradient. The habitat of maximum abundance consists of moist dune valleys characterized by a peaty soil. The soil water, which is practically fresh, has a strongly fluctuating level. The adjacent salt marshes which are periodically inundated by the sea show a lower density of the species. T. limnanthes... |
| Tipo: Article / Letter to the editor |
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| Ano: 1972 |
URL: http://www.repository.naturalis.nl/record/526760 |
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| Ietswaart, J.H.; Offerijns, F.J.M.; Waal, J.H. van der. |
| The Salix pentandra population on the Dutch Wadden island of Schiermonnikoog has been the subject of this study. Chiefly age class composition and sex ratio have been investigated, as well as the distribution of age and sex over the total range. A hypothesis concerning the origin of S. pentandra on the island is proposed. In about 1920 the first two S. pentandra specimens reached Schiermonnikoog, probably as seed. These were both females, so no sexual reproduction took place at all. Not until 1940 a male specimen came to the island and from 1946 onwards the population started to grow exponentially. At the moment the population of this willow counts c. 900 specimens on the island, mainly growing in the central, moist, fresh dune valleys. The oldest specimen... |
| Tipo: Article / Letter to the editor |
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| Ano: 1984 |
URL: http://www.repository.naturalis.nl/record/526939 |
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| Ietswaart, J.H.. |
| The present study deals with the systematics and taxonomy of the genus Origanum (Labiatae, Saturejeae). As this difficult genus was never before monographed, a revisional study was much needed. The data presented are mainly based on the study of herbarium specimens and in some cases of living ones. The picture was completed, as far as possible, with data from various literature sources. A short survey is given of the taxonomic history of Origanum, which goes back as far as Linnaeus, and shows that genus and species concepts of various authors have much differed. A morphological outline of Origanum is given, from which it can be concluded that most generic characters are rather variable. Origanum is characterized in the following ways. Medium sized,... |
| Tipo: Article / Letter to the editor |
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| Ano: 1980 |
URL: http://www.repository.naturalis.nl/record/508224 |
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| Ietswaart, J.H.; Vroman, M.. |
| 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... |
| Tipo: Article / Letter to the editor |
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| Ano: 1974 |
URL: http://www.repository.naturalis.nl/record/527771 |
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