Oenothera linifolia
Oenothera filiformis
threadleaf evening-primrose, threadleaf sundrop
bee-blossom, longflower beeblossom
unbranched or with many ascending branches arising near base, erect, 10–50 cm.
usually well-branched distal to base, (50–)100–400 cm.
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 8–15(–40) × 1.5–3.6 cm, blade lyrate, margins irregularly toothed to lobed;
cauline 1.5–13 × 0.5–3 cm, blade narrowly elliptic to elliptic or lanceolate, margins subentire or shallowly undulate-denticulate.
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.
4-merous, zygomorphic, opening at sunset;
floral tube 4–13(–15) mm;
sepals 7–18 mm;
petals white, fading pink, elliptic to elliptic-obovate, 7–15 mm;
filaments 5–13 mm, anthers 1.5–5 mm, pollen 90–100% fertile;
style 12–34 mm, stigma exserted beyond anthers at anthesis.
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 or ovoid, sharply 4-angled, 4.5–7 × 1.5–2.5 mm;
sessile.
clustered in each locule, ovoid, surface minutely papillose, 1 × 0.5 mm.
2–4, yellowish to reddish brown, 1.3–3 × 0.7–1.3 mm.
= 14.
= 14.
Oenothera linifolia
Oenothera filiformis
Kneiffia linearifolia Spach (1835) is an illegitimate name based on Oenothera linifolia.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
P. H. Raven and D. P. Gregory (1972[1973]) found various levels of hybridization and intergradation between Oenothera filiformis and O. lindheimeri to occur where their ranges overlap. In the region of geographical overlap, most populations of O. filiformis are strigillose in the inflorescences and have evening-opening flowers, while O. lindheimeri is villous in the inflorescences, and has large morning-opening flowers. Moreover, O. lindheimeri occurs only on black clay prairie soil, while O. filiformis occurs in light, sandy soil, as it does throughout its range, and in more disturbed areas. Despite these differences, Raven and Gregory found hybridization between these species scattered across an area from eastern Texas across Louisiana to Alabama. At some locations there is apparently no hybridization, while at others hybrids were uncommon to relatively common. Intermediate morning-blooming plants in Alabama appear to represent evidence of past hybridization since O. lindheimeri does not occur there. Many of the individuals they tested had somewhat reduced pollen fertility (40–70% fertile). They suspected that habitat disturbance was primarily responsible in many cases, but they also detected what may have been intergradation resulting from past hybridization outside of the current distribution of O. lindheimeri. Many of these individual cases deserve further investigation to better understand the dynamics of the interactions between these species and if any of the interactions have led to stabilization of novel populations that might be recognized taxonomically.
Very few collections have been made from areas on the periphery of the range of Oenothera filiformis (southern Ontario, Connecticut, Maryland, Massachusetts, Pennsylvania), and populations in these areas probably represent recent human-based introductions. P. H. Raven and D. P. Gregory (1972[1973]) determined O. filiformis to be self-incompatible.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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