PETERSON, PAUL M.1*, J. TRAVIS COLUMBUS2, ROSA CERROS TLATILPA2, and MICHAEL S. KINNEY2. 1Department of Systematic Biology - Botany, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560-0166; 2Rancho Santa Ana Botanic Garden, Claremont, CA 91711. - Phylogenetics of Muhlenbergia and relatives (Poaceae: Chloridoideae) based on internal transcribed spacer region sequences (nrDNA).
A recent treatment of the subtribe Muhlenbergiinae (Eragrostideae;
Peterson 2000 in Grasses: Systematics and Evolution, Pp. 195-212.)
suggested that Muhlenbergia (a large genus of about 153
species) shares a common ancestor with five smaller genera: Bealia,
Blepharoneuron, Chaboissaea, Lycurus, and Pereilema. An
ongoing phylogenetic study of this group based on internal transcribed
spacer (ITS) region sequences (nrDNA) shows that these five genera are
nested within a paraphyletic Muhlenbergia. In addition, four
chloridoid genera that have been classified outside of the
Muhlenbergiinae are also nested within Muhlenbergia: Aegopogon,
Redfieldia, Schaffnerella, and Schedonnardus. Some well
supported clades (i.e., with many base substitutions and high
jackknife support) in the phylogeny correspond to existing formal and
informal groups within Muhlenbergia. One clade consists
entirely of species of Aegopogon, Muhlenbergia subg.
Muhlenbergia, and Pereilema that exhibit PCK leaf
anatomy. Another clade contains species that correspond to members of
Muhlenbergia subg. Trichochloa (i.e., with sclerosed
phloem in the primary vascular bundles and a crown of inflated cells
just above the primary vascular bundles). Interestingly, ITS sequences
within this clade have diverged little compared to other clades.
Members of the Muhlenbergia montana complex, a group of
caespitose perennials and annuals that usually have a 3-nerved and/or
toothed upper glumes, form a clade. Another clade is composed entirely
of annual species of Muhlenbergia, and Blepharoneuron
tricholepis, a caespitose perennial. Although only 32 species of
Muhlenbergia have been sampled at this writing, it is already
clear that the ITS region will contribute much to our understanding of
the diversification of this lineage.
Key words: Chloridoideae, Eragrostideae, molecular systematics, Muhlenbergia, Muhlenbergiinae, Poaceae