Detlev Drenckhahn

• The island of Rügen (Rugia), located in the Baltic sea, is the most northeastern (NE) part of Germany. Due to its particular geographic position at the border between scandinavian, middle european and continental european floral elements, Rügen harbours several hawkweed species (Hieracia) of the scandinavian area such as Hieracium fuscocinererum, H. subramosum, H. subrigidum and H. diaphanoides subsp. neoornatum and, at the same time, is the most northwestern location of H. echioides. Two endemic Hieracium species have been identified recently,The island of Rügen (Rugia), located in the Baltic sea, is the most northeastern (NE) part of Germany. Due to its particular geographic position at the border between scandinavian, middle european and continental european floral elements, Rügen harbours several hawkweed species (Hieracia) of the scandinavian area such as Hieracium fuscocinererum, H. subramosum, H. subrigidum and H. diaphanoides subsp. neoornatum and, at the same time, is the most northwestern location of H. echioides. Two endemic Hieracium species have been identified recently, i. e. H. muorum subsp. rugianum and H. caesium subsp. zabelianum (Gottschlich et al. 1998, Bot. Rundbr. Mecklenburg-Vorpommern 31:1-94). In the present communication, two further novel endemic Hieracium taxa will be described, which are restricted to the chalk cliffs of Cape Arkona and Jasmund, i. e. H. swantevitii and H. lachenalii subsp. litocretaceum. H. swantevitii (Swantevit’s hawkweed) is intermediate between H. caesium/H. bifidum and H. lachenalii with hairy, modestly glandular involucre and slightly serrated elongated leaves . This view of an intermediate position of H. swantevitii between these species was further supported by the ultrastructure of epidermal papillae of the outer bracts of the involucre visualized by scanning electron microscopy. H. lachenalii subsp. litocretaceum (chalk cliff hawkweed) is characterized by its narrow anguste to almost linear denticulate leaves in combination with mode rately glandular heads. In addition to the description of these two new hawkweed taxa , the rediscovery of three further species will be reported for Rügen, i. e. H. echioides (W. Gager in SE Rügen), H. cymosum subsp. cymosum (close to Göhren in SE Rügen) and H. subrigidum E Glowe in N Rügen. The locality of H. echioides appears to be most north-western site in middle Europe, the locality of H. cymosum is one of the last growth sites in the northern German lowlands and H. subrigidum (so far only known as a single herbarium specimen, collected 1858 in Rügen) has so far not been recorded in other localities of middle Europe.…