Relationships among native and introduced North American species of Hordeum, based on chloroplast DNA restriction-site variation

Restriction-site analysis of chloroplast DNA was carried out on a total of 13 North American species of Hordeum, 7 native and 6 introduced. Sites associated with polymorphic banding patterns were omitted so that only invariant sites within species were used in the analyses. A number of taxa whose species status is in dispute can indeed be supported at species rank, i.e., H. brachyantherum, H. californicum, H. pusillum, H. intercedens, H. marinum, and H. geniculatum. The maternal progenitor of H. arizonicum is H. pusillum, and this is further discussed in light of other possibilities. Both phenetic and cladistic analyses indicate a tripartite relationship whereby H. vulgare is distant from the group of H. leporinum, H. glaucum, and H. murinum and from a second group comprising the native species H. brachyantherum, H. californicum, H. arizonicum, H. jubatum, H. pusillum, H. intercedens, and H. depressum. Hordeum marinum and H. geniculatum occupy a central position in this relationship. Speculation that the putative ancient form of Hordeum resembled a H. murinum – H. geniculatum-like species is discussed. Key words: chloroplast DNA, Hordeum, phylogenetic relationships.