Native or introduced? Problems in the taxonomy and plant geography of some widely introduced annual brome-grasses

Abstract

SynopsisWeedy nature and critical taxonomic status of widespread autogamous annual brome-grasses combine to make assessments of their native phytogeographical areas uncertain or impossible. Suggested criteria for determining native status are reviewed. Some species found in SW Asia occur also in Europe. Some others are so far known only in Europe and may either be native there or introduced from SW Asia. These possibilities are considered by applying native status criteria to 10 principal exemplar species and 4 subspecies. On the basis of known distributions, these criteria suggest that: (i) some species are not native inanyprimary habitats, and perhaps never have been; (ii) though SW Asia seems to be the centre from which the current adaptive radiation ofBromusL. annuals began, not all its brome-grass flora is native, and some of its probable native species are known only as introduced plants in Europe i.e. are undiscovered in SW Asia. It is urged that our imperfect knowledge of distributions in this critical group be remedied by careful analysis of the brome-grass flora of primary habitats in SW Asia.