Herbs (annual or perennial), [shrubs]. Leaves alternate or basal; stipules absent. Flowers usually actinomorphic, rarely slightly zygomorphic (in Oenothera), (3 or)4-merous; stamens 2 times as many, or rarely as many, as sepals; pollen usually shed in monads, rarely tetrads (Chylismia sect. Lignothera). Fruit a dry capsule, usually dehiscent, sometimes indehiscent. Seeds few to numerous, without hairs or wings, [very rarely with asymmetrical dry wing (Xylonagra)], or with dry (Oenothera), erose or smooth wing, or with thick, papillate wings (Chylismiella).
Distribution
North America, Mexico, West Indies, Central America, South America.
Discussion
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).
Selected References
None.