Oenothera riparia
Oenothera arizonica
California evening primrose
erect or ascending, usually many-branched throughout, proximal branches often somewhat spongy, 50–120 cm.
ascending to erect, with decumbent branches, thickened at base, tapering toward apex, 10–35(–60) cm.
in a basal rosette and cauline, softly succulent, 4–13.5 × 0.8–2.1 cm, petiole 0–1.5 cm, blade lanceolate to elliptic-lanceolate, margins remotely denticulate.
in a basal rosette and cauline, basal 5–10(–26) × 0.6–1.5(–3.5) cm, cauline 5–8(–15.5) × 1–2 cm;
petiole 0–12 cm;
blade lanceolate to oblanceolate, margins pinnatifid or sometimes coarsely serrate.
erect, flowers in axils of distalmost few nodes.
opening near sunrise;
buds with free tips 0.5–2(–5) mm, erect to spreading;
floral tube 14–20 mm;
sepals 20–30 mm;
petals bright yellow, fading pale pink or lavender, 16–27 mm;
filaments 10–15 mm, anthers 7–8 mm, pollen 85–100% fertile;
style 15–30 mm, stigma exserted beyond anthers at anthesis.
1–several opening per day near sunset;
buds nodding, weakly quadrangular, without free tips;
floral tube 26–31 mm;
sepals 19–26 mm, conspicuously maroon-spotted, each spot at base of a long hair;
petals white, fading pink to deep pink, broadly obovate or obcordate, 16–26(–36) mm;
filaments 9–15 mm, anthers 7–9 mm;
style 45–50 mm, stigma exserted beyond anthers at anthesis.
oblong-clavate to oblong-ellipsoid, 4-angled or 4-winged, and wings 0.1–0.2 mm, 7–15 × 4–6 mm, stipe 2–5 mm;
sessile.
spreading, woody in age, curved upward, or distal end recurved, cylindrical, obtusely 4-angled, especially toward base, tapering gradually from base to apex, 30–80 × 2.5–3.5 mm;
sessile.
0.8 × 0.4 mm.
numerous, in 1 row per locule, light brown to yellowish brown with dark purple splotches, obovoid, 1.6–2 mm.
= 56.
= 14.
Oenothera riparia
Oenothera arizonica
Oenothera riparia has not been accepted as a distinct species for a long time. The conservative approach used by G. B. Straley (1977) is here followed in recognizing a broadly delimited O. fruticosa, except that the very distinctive coastal tidal-freshwater semi-aquatic octoploid populations (Straley 1982) are recognized as O. riparia. Plants of these coastal populations, which occur from southern Virginia to North Carolina, are more robust, more branched, and less pubescent than those of the two subspecies of O. fruticosa, and have slightly succulent leaves and more prominent adventitious roots (Straley 1982; D. Boufford, pers. comm.). Further field studies and cytological analyses are needed to fully understand the geographical and ecological limits of O. riparia and confirm that it is strictly an octoploid species. K. N. Krakos et al. (2014) determined that Oenothera riparia is self-incompatible and is pollinated by bees (Bombus, Lassioglossum, Megachile, Parallelia, Xylocopa, and Zale).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Oenothera arizonica occurs in southern Arizona from Maricopa and Yuma counties to Cochise County, and from scattered localities in northern Sonora, Mexico, including Cerro Tepopa, Puerto Libertad, and Tastiota. The populations from southwestern Arizona (Yuma County) southward to Sonora often grow on low dunes.
Populations from sand dunes in Yuma County, Cabeza Prieta National Wildlife Refuge, appear to be a large phenotype of Oenothera arizonica that differ from all other specimens in the size of vegetative parts and flowers, and comprise all of the atypical measurements given in the description. Oenothera arizonica typically grows on dunes in Sonora, but rarely so in Arizona. Populations growing on dunes should be studied further and compared to non-dune populations in the northern and eastern portion of the range. Oenothera arizonica is self-compatible (W. L. Wagner et al. 2007; K. E. Theiss et al. 2010).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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