A phylogenetic analysis ofBromus(Poaceae: Pooideae: Bromeae) based on nuclear ribosomal and plastid data, with a focus onBromussect.Bromus

Abstract

To investigate phylogenetic relationships among and within major lineages ofBromus, with focus onBromussect.Bromus, we analyzed DNA sequences from two nuclear ribosomal (ITS, ETS) and two plastid (rpl32-trnLUAG,matK) regions. We sampled 103 ingroup accessions representing 26 taxa ofB. sectionBromusand 15 species of otherBromussections. Our analyses confirm the monophyly ofBromuss.l. and identify incongruence between nuclear ribosomal and plastid data partitions for relationships within and among majorBromuslineages. Results support classification ofB. pumilioandB. gracillimuswithinB. sect.BoissieraandB. sect.Nevskiella, respectively. These species are sister groups and are closely related toB. densus(B. sect.Mexibromus) in nrDNA trees andBromussect.Ceratochloain plastid trees.Bromussect.Bromopsisis paraphyletic. In nrDNA trees, species ofBromussects.Bromopsis,Ceratochloa,Neobromus, andGeneaplusB. rechingeriofB. sect.Bromusform a clade, in whichB. tomentellusis sister to aB. sect.Genea–B. rechingericlade. In the plastid trees, by contrast,B. sect.Bromopsisspecies exceptB. tomentosusform a clade, andB. tomentosusis sister to a clade comprisingB. sect.BromusandB. sect.Geneaspecies. Affinities ofB. gedrosianus,B. pulchellus, andB. rechingeri(members of theB. pectinatuscomplex), as well asB. oxyodonandB. sewerzowii, are discordant between nrDNA and plastid trees. We infer these species may have obtained their plastomesviachloroplast capture from species ofB. sect.BromusandB. sect.Genea. WithinB. sect.Bromus,B. alopecurossubsp.caroli-henrici, a clade comprisingB. hordeaceusandB. interruptus, andB. scopariusare successive sister groups to the rest of the section in the nrDNA phylogeny. Most relationships among the remaining species ofB. sect.Bromusare unresolved in the nrDNA and plastid trees. Given these results, we infer that mostB. sect.Bromusspecies likely diversified relatively recently. None of the subdivisional taxa proposed forBromussect.Bromusover the last century correspond to natural groups identified in our phylogenetic analyses except for a group includingB. hordeaceusandB. interruptus.