Oenothera pilosella
Oenothera filiformis
meadow evening-primrose
bee-blossom, longflower beeblossom
spreading or ascending, unbranched or few-branched distally, 20–80 cm.
usually well-branched distal to base, (50–)100–400 cm.
in a basal rosette and cauline, basal 4–8 × 2–5 cm, petiole (0.5–)1–3(–4) cm, blade oblanceolate to ovate, margins entire;
cauline 3–10(–13) × 1–2(–4) cm, petiole 0–0.5(–2) cm, blade lanceolate to ovate, abruptly narrowed to base, margins subentire or coarsely dentate.
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.
erect, flowers in axils of distalmost few nodes.
opening near sunrise;
buds with free tips 1–3 mm, spreading;
floral tube 10–25 mm;
sepals 10–20 mm;
petals bright yellow, fading pale pink or pale yellow, 15–30 mm;
filaments 7–15 mm, anthers 4–8 mm, pollen 85–100% fertile;
style 10–20 mm, stigma exserted beyond 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.
usually oblong-clavate to oblong-ellipsoid or ellipsoid, 4-angled or weakly 4-winged, (5–)10–15(–28) × 2–4(–5) mm, stipe (1–)3–5(–9) mm;
sessile.
ellipsoid or ovoid, sharply 4-angled, 4.5–7 × 1.5–2.5 mm;
sessile.
1 × 0.5 mm.
2–4, yellowish to reddish brown, 1.3–3 × 0.7–1.3 mm.
= 56.
= 14.
Oenothera pilosella
Oenothera filiformis
Oenothera pilosella is widespread in cultivation in gardens and frequently escapes and becomes naturalized; the northern and eastern natural limits of O. pilosella are not clear. According to G. B. Straley (1977) the natural limits are from Wayne County, West Virginia, along the Ohio River and Erie County, New York, for the eastern limits, and Tuscola County, Michigan, and Manitowoc County, Wisconsin, for the northern limits. K. N. Krakos (2014), based on new field studies and phylogenetic data, found that O. pilosella does not form a monophyletic group with plants previously treated by Straley as O. pilosella subsp. sessilis in molecular analyses, and thus is here reinstated as the distinct species O. sessilis. Straley determined that O. pilosella is self-incompatible and an octoploid, one of the few in the genus.
(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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