Het Schellings havikskruid (Hieracium peleterianum Mérat)

Hieracium peleterianum Mérat subsp. peleterianum is reported from the West-Frisian Island of Terschelling. The plants were found in 12 different localities in the eastern part of the island. The plants studied turned out to be diploid (2n=lß), sexual and selfincompatible. The presence of hybrids (2n=27) between H. pilosella L.(2n=36) and H. peleterianum Mérat (2n=lß) could be demonstrated near Formerum. The hybrid (H. X longisquamum Peter) is completely sterile but spreads vegetatively. The same hybrid can be produced artificially. In most artificial hybrids the diploid H. peleterianum was the pollen-parent, the reciprocal cross did not usually result in the formation of hybrids. The pentaploid form of H. pilosella (which reproduces agamospermously) failed to produce hybrids with H. peleterianum when the latter was used as egg-cell plant. The subspecies peleterianum is usually confined to coastal areas. The Dutch plants agree completely with Danish plants from Jylland and Sjaelland and with Norwegian plants from Oslo, but they differ from French, Swiss and Italian plants of Hieracium peleterianum Mérat subsp. ligericum Zahn in Engler and subsp. subpeleterianum Naegeli et Peter. Cytological examination of all plants collected outside the Netherlands (34 plants from 11 populations) confirmed the diploid chromosome number. The population from Terschelling forms a logical link between the distribution areas north and south of the Netherlands. In the author’s opinion H. peleterianum should be regarded as native not as adventitious.