ARS | Publication request: MOLECULAR INSIGHTS INTO THE TAXONOMY OF GLYCERIA (POACEAE: MELICEAE) IN NORTH AMERICA

Submitted to: American Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 16, 2006
Publication Date: March 22, 2007
Citation: Whipple, I.G., Barkworth, M.E., Bushman, B.S. 2007. Molecular insights into the taxonomy of glyceria (poaceae: meliceae) in north america. American Journal of Botany.

Interpretive Summary: Glyceria (Poaceae: Meliceae) includes approximately 40 species. Eighteen species grow in the United States and Canada, 16 being native to the region. Distinguishing species is impossible using current taxonomic treatments, primarily because of the morphological overlap within two groups of species: G. declinata, G. occidentalis, and G. fluitans and G. striata and G. elata. This study was designed to provide an independent assessment, through chloroplast intergenic DNA sequences, of the morphological delineation that had been developed for the above species. With the notable exception of G. occidentalis, the chloroplast DNA sequences supported recognition of each of the other taxa in our study. Haplotypes of G. occidentalis were present in two clades, one belonging to G. leptostachya and the other to G. fluitans. The most reliable measurable morphological characters for distinguishing among G. leptostachya, G. fluitans, and G. occidentalis were lemma length and anther length. Most measurements for lemma and anther length in Glyceria occidentalis were between those for G. leptostachya and G. fluitans although there was some overlap, chiefly with G. fluitans. We consider that the chloroplast and morphological data favor interpretation of G. occidentalis as a series of natural hybrids between G. leptostachya and G. fluitans.

Technical Abstract: Eighteen Glyceria species grow in the United States and Canada, with 16 being native to the region. We used data from three chloroplast DNA intergenic regions and morphological data to address taxonomic questions concerning Glyceria in North America, particularly the status of G. declinata, G. occidentalis, G. fluitans, G. striata, and G. elata in western North America. The chloroplast data confirmed the presence of two European species, G. declinata and G. fluitans, in western North America. Glyceria occidentalis was exceptional among the taxa studied in having chloroplast genotypes that fell into two different clades, one of which contained G. fluitans and the other the North American species G. leptostachya. The morphological data showed G. occidentalis to be intermediate between G. fluitans and G. leptostachya with respect to their distinguishing characters. Based on these results, we hypothesize that G. occidentalis consists of hybrids between the two species. Glyceria elata and G. striata, which have sometimes been treated as a single species, had different chloroplast genotypes, supporting their recognition as distinct taxa. DNA data from all three intergenic regions was needed for unequivocal identification of the non-hybrid species examined.