GIUSSANI, LILIANA M., J. HUGO COTA-SANCHEZ*, FERNANDO ZULOAGA, AND ELIZABETH A. KELLOGG. Instituto de Botanica Darwinion, Buenos Aires, Argentina; and Department of Biology, University of Missouri-St. Louis, St. Louis, MO 63121. - A molecular phylogeny of the subfamily Panicoideae (Poaceae) using ndhF sequences.
The grass subfamily Panicoideae includes over 3000 species,
approximately 500 of them in the polymorphic and polyphyletic genus
Panicum. We have used full-length sequences of the chloroplast
gene ndhF to determine the phylogeny of the group. The final
data set includes sequences of 102 panicoids plus 6 outgroups; of
these 79 sequences are new to this study. The Panicoideae are
monophyletic, supporting all previous molecular and morphological
studies. The subfamily is divided into three strongly supported
clades, representing groups with the same chromosome base number: the
Andropogoneae (x=10), x=10 Paniceae and x=9 Paniceae; the first two
may be sister taxa, but this result is not strongly supported. The
point of origin of C4 photosynthesis is ambiguous, and varies among
and within strongly-supported clades. The PCK and the NAD-ME C4
subtypes each originated once and are unreversed synapomorphies for
the Urochloa-clade and for Panicum subgenus
Panicum, respectively. All other C4 species are NADP-ME and
lack an outer bundle sheath; despite their biochemical and anatomical
similarity, these do not form a monophyletic group. Panicum
subg. Panicum is unrelated to the other subgenera of
Panicum. Panicum maximum, the sole species in
Panicum subg. Megathyrsus is better placed in
Urochloa, as suggested by earlier authors. Panicum subg.
Agrostoides, subg. Phanopyrum and possibly also subg.
Dichanthelium are polyphyletic. Paspalum is
paraphyletic, with Thrasya derived from within it. All genera
with bristles in the inflorescence (Setaria, Pennisetum, Cenchrus,
Paspalidium) form a clade. Previously defined subtribes are not
monophyletic, but some clades in the phylogeny are similar to those in
morphological cladograms.
Key words: C4 photosynthesis, ndhF, Panicoideae, Panicum, Poaceae