Oenothera linifolia |
Oenothera sessilis |
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threadleaf evening-primrose, threadleaf sundrop |
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Habit | Herbs annual, caulescent, strigillose or glabrous, also often glandular puberulent, especially distally; from a sparsely branched taproot. | Herbs perennial, densely strigillose, glabrate proximally; from fibrous roots. |
Stems | unbranched or with many ascending branches arising near base, erect, 10–50 cm. |
ascending, unbranched to few-branched, 30–65 cm. |
Leaves | in a basal rosette and cauline, basal 1–2(–4) × 0.2–0.6 cm, petiole 0.2–1(–1.5) cm, blade ovate to obovate or narrowly elliptic; cauline 1–4 × less than 0.1 cm, sessile, blade linear or filiform. |
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. |
Inflorescences | nodding, flowers in axils of distalmost few nodes. |
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Flowers | usually 1–3 opening per day near sunrise; buds without free tips; sepals 1.5–2 mm; petals bright yellow, fading pink, obcordate to obovate, 3–5(–7) mm; filaments 1–2 mm, anthers 0.5–1 mm; style 1–2 mm, stigma surrounded by anthers at anthesis. |
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. |
Capsules | ellipsoid-rhombic to subglobose, 4-angled, 4–6(–10) × 1.5–3 mm, stipe 0–4 mm, valve midrib raised at distal end, indehiscent or tardily dehiscent distally; sessile. |
ellipsoid, 4-angled, 8–10 × 3–4 mm, stipe 0–2 mm; sessile. |
Seeds | clustered in each locule, ovoid, surface minutely papillose, 1 × 0.5 mm. |
1 × 0.5 mm. |
2n | = 14. |
= 56. |
Oenothera linifolia |
Oenothera sessilis |
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Phenology | Flowering Apr–Jun(–Aug). | Flowering May–Jun. |
Habitat | Prairies, open woodlands, open rocky and sandy sites, roadsides. | Moist remnant prairies in sandy or silty soil. |
Elevation | 0–400 m. (0–1300 ft.) | 0–100 m. (0–300 ft.) |
Distribution |
AL; AR; FL; GA; IL; KS; KY; LA; MO; MS; NC; OK; SC; TN; TX
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AR; LA; TX |
Discussion | Kneiffia linearifolia Spach (1835) is an illegitimate name based on Oenothera linifolia. (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.) |
Source | FNA vol. 10. | FNA vol. 10. |
Parent taxa | Onagraceae > subfam. Onagroideae > tribe Onagreae > Oenothera > sect. Peniophyllum | Onagraceae > subfam. Onagroideae > tribe Onagreae > Oenothera > sect. Kneiffia |
Sibling taxa | ||
Synonyms | Kneiffia linifolia, O. linifolia var. glandulosa, Peniophyllum linifolium | Kneiffia sessilis, O. pilosella subsp. sessilis, O. pilosella var. sessilis |
Name authority | Nuttall: J. Acad. Nat. Sci. Philadelphia 2: 120. (1821) | (Pennell) Munz: Bull. Torrey Bot. Club 64: 291. (1937) |
Web links |