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A molecular phylogeny of the grass subfamily Panicoideae (Poaceae) shows multiple origins of C 4 photosynthesis
DNA sequence data from the chloroplast gene ndhF were analyzed to estimate the phylogeny of the subfamily Panicoideae, with emphasis on the tribe Paniceae. Our data suggest that the subfamily is divided into three strongly supported clades, corresponding to groups with largely identical base chromos...
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Published in: | American journal of botany 2001-11, Vol.88 (11), p.1993-2012 |
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Main Authors: | , , , |
Format: | Article |
Language: | English |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | DNA sequence data from the chloroplast gene
ndhF
were analyzed to estimate the phylogeny of the subfamily Panicoideae, with emphasis on the tribe Paniceae. Our data suggest that the subfamily is divided into three strongly supported clades, corresponding to groups with largely identical base chromosome numbers. Relationships among the three clades are unclear. In unweighted parsimony analyses, the two major clades with
x
= 10 (Andropogoneae and
x
= 10 Paniceae) are weakly supported as sister taxa. The third large clade corresponds to
x
= 9 Paniceae. In analyses under implied weight, the two clades of Paniceae are sisters, making the tribe monophyletic. Neither resolution is strongly supported.
Our molecular phylogenies are not congruent with previous classifications of tribes or subtribes. Based on this sample of species, we infer that C
4
photosynthesis has evolved independently several times, although a single origin with multiple reversals and several reacquisitions is only slightly less parsimonious. The phosphoenol pyruvate carboxykinase (PCK) subtype of C
4
photosynthesis has evolved only once, as has the NAD‐malic enzyme (ME) subtype; all other origins are NADP‐ME. Inflorescence bristles are apparently homologous in the genera
Setaria
and
Pennisetum
, contrary to opinions of most previous authors. Some genera, such as
Digitaria, Echinochloa
, and
Homolepis
are supported as monophyletic. The large genus
Paspalum
is shown to be paraphyletic, with
Thrasya
derived from within it. As expected,
Panicum
is polyphyletic, with lineages derived from multiple ancestors across the tree.
Panicum
subg.
Panicum
is monophyletic.
Panicum
subg.
Dichanthelium
, subg.
Agrostoides
, and subg.
Phanopyrum
are unrelated to each other, and none is monophyletic. Only
Panicum
subg.
Dichanthelium
sect.
Dichanthelium
, represented by
P. sabulorum
and
P. koolauense
, is monophyletic.
Panicum
subg.
Megathyrsus
, a monotypic subgenus including only the species
P. maximum
, is better placed in
Urochloa
, as suggested by other authors. |
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ISSN: | 0002-9122 1537-2197 |
DOI: | 10.2307/3558427 |