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 of Bromus, with focus on Bromus sect. 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 of B. section Bromus and 15 species of other Bromus sections. Our analyses confirm the monophyly of Bromus s.l. and identify incongruence between nuclear ribosomal and plastid data partitions for relationships within and among major Bromus lineages. Results support classification of B. pumilio and B. gracillimus within B. sect. Boissiera and B. sect. Nevskiella, respectively. These species are sister groups and are closely related to B. densus (B. sect. Mexibromus) in nrDNA trees and Bromus sect. Ceratochloa in plastid trees. Bromus sect. Bromopsis is paraphyletic. In nrDNA trees, species of Bromus sects. Bromopsis, Ceratochloa, Neobromus, and Genea plus B. rechingeri of B. sect. Bromus form a clade, in which B. tomentellus is sister to a B. sect. Genea–B. rechingeri clade. In the plastid trees, by contrast, B. sect. Bromopsis species except B. tomentosus form a clade, and B. tomentosus is sister to a clade comprising B. sect. Bromus and B. sect. Genea species. Affinities of B. gedrosianus, B. pulchellus, and B. rechingeri (members of the B. pectinatus complex), as well as B. oxyodon and B. sewerzowii, are discordant between nrDNA and plastid trees. We infer these species may have obtained their plastomes via chloroplast capture from species of B. sect. Bromus and B. sect. Genea. Within B. sect. Bromus, B. alopecuros subsp. caroli-henrici, a clade comprising B. hordeaceus and B. interruptus, and B. scoparius are successive sister groups to the rest of the section in the nrDNA phylogeny. Most relationships among the remaining species of B. sect. Bromus are unresolved in the nrDNA and plastid trees. Given these results, we infer that most B. sect. Bromus species likely diversified relatively recently. None of the subdivisional taxa proposed for Bromus sect. Bromus over the last century correspond to natural groups identified in our phylogenetic analyses except for a group including B. hordeaceus and B. interruptus.

What Hides in the Heights? The Case of the Iberian Endemism Bromus picoeuropeanus

“…The trees and networks based on trnL presented large groups formed by many different species, with B. erectus and B. picoeuropeanus found in the section Bromopsis group. These results are similar to those of Nasiri et al [ 51 ], who used a similar methodology to study the phylogenetic relationship within sect. Bromus and determined that neither the ITS nor the plastid markers were capable of discriminating at the species level, while the combination of ITS and ETS allowed them to be discriminated at species level.…”

“…Since previous molecular studies have revealed that the section Bropmosis , in which B. picoeuropeanus was classified by Rico and Acedo [ 54 ], is polyphyletic e.g., [ 14 , 51 ], sequences from different Bromus sections generated in previous studies were included in the analyses. The newly generated sequences together with Bromus sequences from previous studies available at GenBank (see Table S1 ) were used to generate several datasets: the ITS dataset, ETS dataset, trnL dataset, nuclear dataset, and the combined dataset.…”

Characterization and Comparative Analysis of Complete Chloroplast Genomes of Four Bromus (Poaceae, Bromeae) Species

“…B. inermis , B. benekenii , and B. riparius , which all belong to Bromopsis , constitute several independent lineages and are not clustered into a single clade, which is in agreement with the results of Saarela and Pillay [ 13 , 14 ]. Nasiri [ 1 ] found that Bromeae sect. Genea is not monophyletic in plastid trees.…”

“…Pillay [ 13 ] analyzed the enzyme cleavage sites of Bromus using phylogenetic information and obtained a simple phylogenetic chart, which provided a preliminary analysis of the genetic relationships of Bromus . Saarela and Nasiri [ 1 , 14 ] confirmed the monophyletic nature of Bromus . However, the ribosomal and cp data were inconsistent for the Bromus major lineage.…”

“…Bromus (Poaceae Bromeae) is an important forage grass with annual, biennial, and perennial growth [ 1 ]. It is mainly found in Europe, Asia, America, and Africa, and is highly adaptable to drought, salinity, and cold [ 2 ].…”