Oenothera sect. Lavauxia
(when present) ascending [or decumbent].
in a basal rosette, sometimes also cauline, (4–)8–36 cm;
blade margins coarsely pinnatifid or lobed to dentate or subentire.
solitary flowers in axils of leaves.
opening near sunset, with a slightly sweet fragrance and a spermaceous background odor, or nearly unscented;
buds erect, obtusely quadrangular, with unequal or subequal free tips;
floral tube (20–)40–200(–265) mm;
sepals splitting along one suture, remaining coherent and reflexed as a unit at anthesis or separating in pairs;
petals yellow [white], fading orange to lavender, drying purple to lavender or purplish brown, obovate with acute apex or obcordate;
stigma deeply divided into 4 linear lobes.
leathery or woody in age, usually narrowly ovoid or ellipsoid to rhombic-obovoid, sometimes ovoid or lanceoloid, winged, wings oblong to triangular in distal [1/2–]2/3 of capsule, constricted to a short beak, dehiscent 1/4–1/2 their length;
sessile.
numerous, usually in 2 rows per locule, rarely 3 adjacent and distinct rows (O. triloba), asymmetrically cuneiform, narrowly winged distally, also along one adaxial margin, surface minutely beaded.
= 14.
Oenothera sect. Lavauxia
Species 5 (3 in the flora).
Section Lavauxia consists of five diploid (n = 7) species, divided into two subsections, which are locally common in seasonally wet depressions, flats, meadows, stream banks, or disturbed sites from southern Canada through the western and east-central United States to central Mexico, disjunct in Baja California, and two species in southern South America, at 0–3200 m elevation. The monophyly of sect. Lavauxia is strongly supported, but its relationships to the rest of the genus are obscure. No member of the South American subsect. Australis has been included in molecular analyses, but it shares unique morphological features with the North American subsect. Lavauxia; the monophyly of this section is not in doubt, based on the shared dandelionlike acaulescent habit and unique capsule morphology. Species are self-compatible or, rarely, apparently self-incompatible (some plants of O. acutissima); flowers vespertine, fragrance pungent, often slightly sweet with a spermaceous background scent in O. acutissima and outcrossing populations of O. flava, or without noticeable scent in autogamous populations of O. flava and in O. triloba. Species are outcrossing and pollinated by hawkmoths (O. acutissima and large-flowered populations of O. flava) or autogamous, occasionally cleistogamous in O. flava (W. L. Wagner et al 2007; R. A. Raguso et al. 2007; H. E. Summers et al. 2015).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
