Flora of North America species comparison

Bouteloua curtipendula is a common, often dominant or co-dominant species in open grasslands and wetlands of the drier portions of the central grasslands of North America. It is highly regarded as a forage species and is also an attractive ornamental. Its range extends from the Flora region through Mexico and Central America to western South America.

As the range of chromosome numbers suggests, B. curtipendula is an apomictic species. There are three varieties. Two of the three grow in the Flora region; the third, B. curtipendula var. tenuis Gould & Kapadia, is endemic to Mexico.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

The subfamily Chloridoideae is most abundant in dry, tropical and subtropical regions. In the Flora region, it reaches its greatest diversity in the southwestern United States (Barkworth and Capels 2000). Almost all its members, and all those in the Flora region, have C4 photosynthesis. Most employ the NAD-ME or PCK pathways, but Pappophorum utilizes the NADP-ME pathway.

The subfamily has been recognized, with essentially the same limits as here, for some time, although reservations have been expressed concerning its monophyly (Campbell 1985; Jacobs 1987; Kellogg and Campbell 1987). More recent studies, both morphological (Van den Borre and Watson 1997, 2000) and molecular (Soreng and Davis 1998; Hilu et al. 1999; Hsaio et al. 1999; Grass Phylogeny Working Group 2001; Hilu and Alice 2001) support its recognition as a monophyletic unit. There is less agreement concerning the subfamily's closest relative, some studies pointing to the Arundinoideae (Grass Phylogeny Working Group 2001) and some to the Danthonioideae (Barker et al. 1995; Hilu and Esen 1993; Hilu and Alice 2001).

There is considerable disagreement concerning the tribal treatment within the Chloridoideae, the number of tribes recognized varying from two (Prat 1936) to eight (Gould and Shaw 1983). Hilu and Wright (1982, p. 28) concluded, on the basis of their morphological study, that "... the boundaries between most of the tribes in this subfamily are not pronounced." They noted that Savile (1979) reached the same conclusion from considering the host specificity of various pathogenic fungi.

More recent work supports Hilu and Wright's conclusion. Van den Borre and Watson (1997, 2001) recognized eight informal groups within the subfamily. Five of the groups were large, the smallest including around 133 species and the largest around 380. The other three groups, which correspond to the Orcuttieae, Pappophoreae, and subtribe Triodiinae, include 9, 42, and 54 species, respectively. The difference in size is of no concern; the fact that all three of the small groups are embedded within one of the five large groups, the Pappophoreae and Triodiinae in a group than includes Eragrostis subg. Eragrostis and the Orcuttieae in the group that includes Muhlenbergia, is disturbing. Van den Borre and Watson noted that part of the problem was that that Eragrostis, and probably some of the other large genera, are not monophyletic.

Hilu and Alice (2001) recognized four clades within the Chloridoideae. Like Van den Borre and Watson, they found the Orcuttieae and Triodiinae to be monophyletic, although their placement within the subfamily was not clear. Unlike Van den Borre and Watson, Hilu and Alice found Pappophorum, and hence the Pappophoreae, to be polyphyletic.

The treatment presented here is conservative in recognizing the Orcuttieae and Pappophoreae as distinct tribes. It departs from most other treatments in merging all other North American taxa into a single tribe, the Cynodonteae. Consensus on how the Cynodonteae sensu lato should be broken up is unlikely to be reached until the generic limits of its members have been more thoroughly examined.

(Discussion copyrighted by Flora of North America; reprinted with permission.)