Flora of North America species comparison

Subspecies crinita is the most polymorphic subspecies of Oenothera cespitosa; it is also the least understood. W. L. Wagner et al. (1985) grouped two series of populations that appear to intergrade together within the limits of this subspecies. One population is a morphologically relatively uniform form characterized by a many-branched habit, which may form dense clumps to 50 cm diameter, leaves that are 2–7 cm, floral tubes 25–60 mm and petals that fade to a rose color, and it occurs at high elevations on rocky, limestone sites or at lower elevations on extreme, chalky, white limestone and dolomite substrates or sometimes scree slopes. A more common form occurs at low to mid elevations in pinyon-juniper woodlands to Great Basin or Mojave Desert scrub on rocky slopes, talus, or along arroyos that is much less compact with one to several clustered rosettes, rarely more, with leaves 8–16 cm, floral tubes 45–75 mm, and petals that fade rose purple. The common form also grows on limestone and dolomite but, unlike the clumped form, it does not seem to be restricted to it. To compound the problem, many foothill and valley populations of subsp. crinita intergrade extensively with subspp. cespitosa and marginata.

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

Genera 22, species 664 (17 genera, 277 species in the flora).

Members of the Onagraceae are especially richly represented in North America. The family comprises annual and perennial herbs, with some shrubs and a few small to medium-sized trees. Most species occur in open habitats, ranging from dry to wet, with a few species of Ludwigia aquatic, from the tropics to the deserts of western North America, temperate forests, and arctic tundra; some species of Epilobium, Ludwigia, and Oenothera can be weeds in disturbed habitats. Members of the family are characterized by 4-merous flowers (sometimes 2-, 5-, or 7-merous), an inferior ovary, a floral tube in most species, stamens usually two times as many as sepals, and pollen connected by viscin threads. Flowers are usually bisexual, sometimes unisexual, and plants are gynodioecious, matinal, diurnal, or vespertine, self-compatible or self-incompatible, often outcrossing and then pollinated by a wide variety of insects or birds, or autogamous (P. H. Raven 1979; W. L. Wagner et al. 2007).

Onagraceae are known in considerable systematic detail, and information is available on comparative breeding systems and pollination biology, on chromosome numbers and cytogenetic relations, often involving translocations, and on vegetative, floral, and seed anatomy, palynology, and embryology. The phylogeny of the family is known in reasonably good detail, with most parts of the trees generally well-supported.

The suprageneric and generic classification presented by W. L. Wagner et al. (2007) differs in a number of ways from the previous classification (P. H. Raven 1979, 1988). Onagraceae are divided into two subfamilies based on a fundamental basal split recognized in all phylogenetic studies (R. H. Eyde 1981; P. C. Hoch et al. 1993; R. A. Levin et al. 2003, 2004; V. S. Ford and L. D. Gottlieb 2007), with Ludwigia on one branch (as Ludwigioideae), and the rest of the family on a second branch (as Onagroideae). Onagroideae are subdivided into six tribes: Circaeeae (including Fuchsieae), Epilobieae, Gongylocarpeae, Hauyeae, Lopezieae, and Onagreae. The Epilobieae and Onagreae are diverse; together they constitute fully two-thirds of the species in the family and include 15 of the 22 genera. The classification following Wagner et al. can be viewed on the Onagraceae web site by Wagner and Hoch at http://botany.si.edu/Onagraceae.

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