Oenothera primiveris
Oenothera sessilis
desert evening primrose, yellow desert evening primrose
(when present) unbranched and erect or, sometimes, few branches from near base, in robust plants stems and caudex hollow and greatly enlarged, especially toward base, densely leafy, 5–35 cm.
ascending, unbranched to few-branched, 30–65 cm.
in a basal rosette, sometimes also cauline, (1.4–)6–15(–28) × (0.2–)1–3.5(–5.6) cm;
petiole (0.9–)3.5–8(–14) cm;
blade oblanceolate to linear-oblanceolate, pinnatifid or 2-pinnatifid to shallowly pinnately lobed, margins sinuate-dentate or subentire, apex obtuse.
in a basal rosette and cauline, basal 2.5–7 ×0.7–2.3 cm, petiole 1–1.5 cm, blade oblanceolate, margins subentire, undulate;
cauline (3–)6–7(–9) ×(0.3–)0.6–0.8(–1.1) cm, sessile, blade lanceolate to narrowly lanceolate, margins subentire.
nodding, flowers in axils of distalmost few nodes.
usually 1–4, rarely more, opening per day, 1–2 hours before sunset;
sepals (7–)12–25(–30) mm;
petals yellow, fading reddish orange to purple, obcordate to obovate, (6–)13–35(–40) mm;
filaments 6–16 mm, anthers 3–10 mm;
style (32–)40–90(–100) mm, stigma exserted beyond anthers or surrounded by them.
opening near sunrise;
buds with free tips 1–2 mm, connivent to spreading;
floral tube 10–15(–20) mm;
sepals 10–18 mm;
petals bright yellow, fading pale pink, 15–25 mm;
filaments 7–9 mm, anthers 5–8 mm, pollen 85–100% fertile;
style 10–12 mm, stigma exserted beyond anthers at anthesis.
woody in age, sigmoid or curved to nearly straight, lanceoloid to ovoid, 4-angled, 10–45(–60) × 4–8 mm, beak 4–15 mm, dehiscent 1/4–2/3 their length;
sessile.
ellipsoid, 4-angled, 8–10 × 3–4 mm, stipe 0–2 mm;
sessile.
usually numerous, in 2 rows per locule, obovoid to oblanceoloid, 3–3.5 × 1–1.4 mm, surface thickened above raphe and at distal end into U-shaped structure.
1 × 0.5 mm.
= 14.
= 56.
Oenothera primiveris
Oenothera sessilis
Oenothera primiveris has a complex variation pattern (W. L. Wagner 2005). In the western part of the range from southeastern California across southern Nevada to southern Utah counties of Emery, Kane, and Washington, and northwestern Mohave County, Arizona, plants generally have a gray appearance, with dense pubescence and larger flowers with widespread self-compatibility, but with scattered populations retaining self-incompatibility. Populations from southof the Mogollon Plateau to southern New Mexico, western Texas, Chihuahua, Sonora, and Baja California, Mexico, are greener in appearance with smaller to much smaller flowers, and are all self-compatible with occasional outcrossing or complete autogamy. The transitions between these two extremes are so extensive and more or less gradual that it is not possible to subdivide into two subspecies as has been done previously (Wagner).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Oenothera sessilis is relatively rare within its range and has a narrow overall distribution, occurring in Ashley, Phillips, Prairie, and St. Francis counties in Arkansas, Allen, Claiborne, and Tensas parishes in Louisiana, and Galveston County in Texas. Oenothera sessilis appears to be relatively rare and may no longer occur in Texas; it was last collected there in the 1840s by Lindheimer on Galveston Island. It is also rare in Louisiana but has been collected in recent decades. It is currently most common in Arkansas. P. A. Munz (1937, 1965) treated this taxon as O. sessilis, but G. B. Straley (1977) in his revision of sect. Kneiffia placed it as a subspecies of O. pilosella based on a common octoploid (2n = 56) chromosome number, morphology, and field studies. K. N. Krakos et al. (2014), based on new field studies, controlled greenhouse breeding experiments, and phylogenetic data found that this taxon differs morphologically from O. pilosella by having consistently shorter stature and smaller flowers, is self-compatible, and does not form a monophyletic group with O. pilosella in molecular analyses, and is here reinstated as a distinct species.
Oenothera sessilis is in the Center for Plant Conservation’s National Collection of Endangered Plants as O. pilosella subsp. sessilis.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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