Morphological variation in Bromus sect. Ceratochloa germplasm of Patagonia

Abstract

South American representatives of Bromus sect. Ceratochloa make up a morphologically diverse group of grasses indigenous to the southern Andes of Argentina and Chile. The objectives of the present study were to describe patterns of morphological variation among 30 accessions representing six species (Bromus catharticus Vahl, Bromus coloratus Steud., Bromus lithobius Trin., Bromus mango E. Desv., Bromus stamineus E. Desv., and Bromus tunicatus Phil.) in a common garden, correlate morphological and previously obtained molecular data, and develop a taxonomic treatment within sect. Ceratochloa of South America. Plant materials included 28 hexaploid (2n = 6x = 42) and 2 octoploid (2n = 8x = 56) accessions. Based on multivariate analyses of 24 characters, the two octoploid accessions formed an isolated, well-defined group, while the hexaploids formed two less-defined groups. Characterized by lemma awns longer than 3 mm, one group consisted of those accessions of B. coloratus, B. lithobius, and B. stamineus, whereas the other group consisted of B. catharticus, B. mango, and B. tunicatus. A significant Mantel test statistic (r = 0.70, P = 0.001) suggested a high correlation between morphological variation and DNA polymorphism. Taken together, our results indicated that the hexaploid complex should be described as a single variable species (B. cathar ticus), with two nearly continuous groups: B. catharticus subsp. catharticus (Vahl) Herter and B. catharticus subsp. stamineus (E. Desv.) Massa. Based on nomenclature priority and type specimen designations, the octoploid accessions should be described as Bromus coloratus.Key words: Bromus, morphology, multivariate analysis, Patagonia, taxonomy.