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FNA | Family List | FNA Vol. 10 | Onagraceae | Oenothera

51. Oenothera filiformis (Small) W. L. Wagner & Hoch, Syst. Bot. Monogr. 83: 212. 2007.

Gaura filiformis Small, Bull. Torrey Bot. Club 25: 617. 1898; G. biennis Linnaeus var. pitcheri Torrey & A. Gray; G. filiformis var. kearneyi Munz; G. longiflora Spach 1836, not Oenothera longiflora Linnaeus 1753

Herbs usually robust winter-annual, sometimes biennial, moderately to densely strigillose, sometimes also glandular puberulent, villous and/or short-hirtellous; from fleshy taproot. Stems usually well-branched distal to base, (50–)100–400 cm. Leaves 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. Flowers 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. Capsules ellipsoid or ovoid, sharply 4-angled, 4.5–7 × 1.5–2.5 mm; sessile. Seeds 2–4, yellowish to reddish brown, 1.3–3 × 0.7–1.3 mm. 2n = 14.

Flowering (Jun–)Jul–Oct(–Nov). Open woods, fields, along streams, sandy soil, disturbed sites, ditch banks, roadsides, railway embankments; 10–500 m; Ont.; Ala., Ark., Colo., Conn., Ill., Ind., Iowa, Kans., Ky., La., Md., Mass., Mich., Miss., Mo., Nebr., Ohio, Okla., Pa., Tenn., Tex., Wis.

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.


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