Chloroplast Dna Variation and the Phylogeny of Hordeum (Poaceae)

Restriction site variation in the chloroplast genome (cpDNA) was surveyed among 37 taxa or cytotypes (40 accessions) of the genus Hordeum. Seventeen restriction enzymes were employed, and a total of 491 restriction sites were assayed. Of these, 120 were variable among the taxa, including 70 synapomorphies. The level of sequence divergence (p) among species of Hordeum varied from 0.0 to 0.017, indicating that Hordeum possesses an about‐average level of cpDNA diversity as compared to most other genera of flowering plants for which data are available. Wagner and polymorphism parsimony phytogenies were constructed from the restriction site data. These analyses divided the genus into several distinct groups; 1) American taxa; 2) diploid H. marinum; 3) Asian taxa; 4) H. vulgare‐H. bulbosum; and 5) the H. murinum complex. Bootstrap‐based confidence limits provided statistical support for the monophylesis of the latter three groups. The cpDNA data showed remarkably good congruence with previously published isoenzymatic, molecular, cytological, and crossing data.