Oenothera sessilis
Calylophus tubicula
(synonym of Oenothera tubicula)
ascending, unbranched to few-branched, 30–65 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.
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.
ellipsoid, 4-angled, 8–10 × 3–4 mm, stipe 0–2 mm;
sessile.
1 × 0.5 mm.
= 56.
Oenothera sessilis
Calylophus tubicula
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.)
Subspecies 2 (1 in the flora).
H. F. Towner (1977) found that Oenothera tubicula is self-incompatible and diurnal with opening times just prior to sunrise. It occurs primarily on limestone soil in arid lowlands, but occasionally in montane areas, from Guadalupe County, New Mexico, south to western Texas, northeast to Howard County, Texas, and south to northern Zacatecas, south-central Nuevo León, and southwestern Tamaulipas, 600–1800 m. Subspecies strigulosa (Towner) W. L. Wagner & Hoch is known only from rocky, open sites and canyons in relatively montane areas, sometimes in pine forests in southernmost Coahuila, south-central Nuevo León, and southeastern Tamaulipas, from 1500 to 2300 m. It differs in being strigillose on the ovary and distally on stems, leaves linear to narrowly lanceolate, and the petals fading red or purple.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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