Oenothera sessilis
Oenothera coloradensis
Colorado beeblossom
ascending, unbranched to few-branched, 30–65 cm.
1–few-branched from base, 50–80(–100) cm.
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.
in a basal rosette and cauline, basal 4–18 × 1.5–4 cm, blade very narrowly elliptic, lanceolate, or oblanceolate;
cauline 5–13 × 1–4 cm, blade narrowly elliptic, narrowly lanceolate, or narrowly oblanceolate, margins subentire or repand-denticulate.
nodding, flowers in axils of distalmost few nodes.
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.
4-merous, zygomorphic, opening at sunset;
floral tube 8–12 mm;
sepals 9.5–13 mm;
petals white, fading pink, rhombic-obovate, 7–12 mm;
filaments 6.5–9 mm, anthers 2.5–4 mm, pollen 90–100% fertile;
style 19–25 mm, stigma exserted beyond anthers at anthesis.
ellipsoid, 4-angled, 8–10 × 3–4 mm, stipe 0–2 mm;
sessile.
ellipsoid or ovoid, sharply 4-angled, with fairly deep furrows alternating with angles, 6–8.5 × 2–3 mm;
sessile.
1 × 0.5 mm.
1–4, yellowish to light brown, 2–3 × 1 mm.
= 56.
= 14.
Oenothera sessilis
Oenothera coloradensis
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.)
Oenothera coloradensis is currently known from fewer than two dozen populations from southern Laramie and Platte counties in Wyoming, northern Weld County, Colorado, formerly near Fort Collins, Larimer County, Colorado, and in western Kimball County, Nebraska. It is federally listed as a threatened species in the United States. The primary threats are agricultural use of habitat, herbicide spraying to control weed species, and livestock trampling and grazing (see W. L. Wagner et al. 2013). Recent study by K. N. Krakos (unpubl.) has determined this species to be self-compatible. P. H. Raven and D. P. Gregory (1972[1973]) described this species as glandular puberulent in inflorescence, which was repeated in the recent revised taxonomy (Wagner et al.); however, examination of specimens show that P. A. Munz (1965) was correct in describing the pubescence of the inflorescence as non-glandular.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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