Flora of North America species comparison

Clarkia rhomboidea is a tetraploid derived from C. mildrediae and C. virgata or a closely related species. The six diploid species in sect. Myxocarpa closely related to C. rhomboidea (C. australis, C. borealis, C. mildrediae, C. mosquinii, C. stellata, and C. virgata) are California endemics with relatively small areas of distribution, whereas C. rhomboidea occurs throughout much of the western United States and is morphologically much more variable. Clarkia rhomboidea characteristically has relatively small, self-pollinating flowers with the stigma in contact with the anthers. Among the diploid species only C. stellata has similar small, self-pollinating flowers but is distinguished by yellow pollen and petals with a shallowly 3-lobed blade that is not flecked. Rare populations of C. rhomboidea have relatively large flowers with the stigma exserted beyond the anthers. When they occur within the geographical range of the outcrossing diploid species, they may be difficult to distinguish without determining chromosome number.

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

Genera 13, species 265 (12 genera, 199 species in the flora).

Onagreae account for more than half the total genera in Onagraceae and diversified from a center in southwestern North America (L. Katinas et al. 2004). Delimitation of the tribe by W. L. Wagner et al. (2007) differs from previous ones by the exclusion of Gongylocarpus, now in its own tribe, by the segregation of eight genera (Camissoniopsis, Chylismia, Chylismiella, Eremothera, Eulobus, Neoholmgrenia, Taraxia, and Tetrapteron) from Camissonia, and by the inclusion of three previously separate genera (Calylophus, Gaura, and Stenosiphon) in Oenothera. Within the branch of the family that lacks stipules (Gongylocarpeae, Epilobieae, and Onagreae), the last two tribes form a clade that has very strong molecular support (R. A. Levin et al. 2003, 2004), but no obvious morphological synapomorphy. The clade may be defined by a cytogenetic change from the base chromosome number of x = 11 found in Circaeeae, Gongylocarpeae, and Lopezieae, to x = 18 in Epilobieae, and x = 7 in Onagreae; however, these changes could also have occurred independently. Other than the new chromosome number x = 7, the only apparent morphological synapomorphy for Onagreae alone is pollen with prominent apertural protrusions (J. Praglowski et al. 1987, 1989), a character state also found in Circaeeae (Praglowski et al. 1994). The monophyly of Onagreae has moderate (Levin et al. 2004) to strong support (V. S. Ford and L. D. Gottlieb 2007).

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