ECOGEOGRAPHY OF THE GRASS GENUS HELICTOTRICHON (POACEAE, AVENEAE) IN THE MEDITERRANEAN AND ADJACENT REGIONS

The geographical distribution of the grass genus Helictotrichon in the Mediterranean Region is analysed and mapped for 33 taxa. Based on onl y a single life form (perennial herb), a variety of edaphically, clima tically and altitudinally differently adapted species complexes has ev olved in the area. Most of these complexes show west-east disjunctions and contain geographically, sometimes even edaphically vicarious taxa with complementary distribution. A transition from mesomorphic to xer omorphic habit occurred independently in different species groups and led to the establishment of the ''modern'' Mediterranean taxa which ar e in part highly polyploid derivatives of more mesophilic diploids. Th e significance of polyploidy, patterns of parapatric and sympatric dis tribution, biogeographical borders, and centres of species diversity a re discussed in context with the history of the Mediterranean vegetati on. New combinations are: Helictotrichon setaceum subsp. petzense, H. pratense subsp. lusitanicum, H. praetutianum.