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

38. Epilobium oreganum Greene, Pittonia. 1: 225. 1887.
[C E]

Grant’s Pass willowherb

Epilobium glaucum Howell, Howell’s Pacific Coast Pl., no. 1139. 1887, not Philippi 1864; E. brevistylum Barbey var. exaltatum (Drew) Jepson; E. californicum Haussknecht var. exaltatum (Drew) Jepson; E. exaltatum Drew; E. glandulosum Lehmann var. exaltatum (Drew) Munz; E. subcaesium Greene

Herbs with leafy basal rosettes or short shoots. Stems several to many, ascending or erect, terete, loosely clumped, 40–100 cm, usually well-branched apically, ± glabrous and glaucous proximal to inflorescence, without distinct raised lines, sparsely mixed strigillose and glandular pubescent proximally. Leaves opposite proximal to inflorescence, alternate distally, petiole broad, 1–3 mm; blade narrowly lanceolate to narrowly ovate, 3–9 × 0.7–2.5 cm, base rounded to cuneate, mar­gins finely serrulate, 20–40 teeth per side, veins red­dish green, conspicuous, 6–10 per side, apex acute, surfaces glabrous and often glaucous, crowded proximally; bracts much reduced and narrower. Inflorescences erect racemes or open panicles, often branched, glandular puberulent, sometimes mixed strigillose. Flowers erect; buds 5–8 × 2–3.5 mm, often with stigma exserted; pedicel 2–4 mm; floral tube 2–3 × 1.8–3 mm, with ring of spreading hairs near base of tube inside; sepals often flushed red, 6–10 × 2.1–2.8 mm, abaxial surface mixed strigillose and glandular puberulent; petals dark pink to rose-purple, (6–)10–15 × 4.5–6 mm, apical notch 2.6–3 mm; filaments cream or light pink, those of longer stamens 6–8 mm, those of shorter ones 3.5–4.5 mm; anthers cream or yellow, 1–1.2 × 0.5–0.6 mm; ovary 20–25 mm, densely glandular puberulent and mixed strigillose; style cream or yellow, 9–13 mm, stigma broadly and sometimes irregularly 4-lobed, 1–1.5 × 2.1–2.9 mm, exserted beyond anthers. Capsules 25–45 mm, surfaces mixed sparsely glandular puberulent and strigillose, often with reduced fertile seed set; pedicel 3–6 mm. Seeds narrowly obovoid, 0.9–1.3 × 0.4–0.5 mm, chalazal collar 0.1–0.15 × 0.2–0.25 mm, gray-brown, surface with conspicuous parallel longitudinal ridges of laterally flattened papillae; coma readily detached, white, 4–6 mm. 2n = 36.

Flowering Jul–Aug(–Sep). Damp seeps, swampy areas, stream banks; of conservation concern; 200–500 m; Calif., Oreg.

Epilobium oreganum is endemic to a small region of southern Oregon (Douglas and Josephine counties, mainly from Grants Pass south along the Illinois River) and northern California (Del Norte, Humboldt, Siskiyou, Tehama, and Trinity counties, especially along the South Fork of the Trinity and Klamath rivers).

Epilobium oreganum is the only other species that shares the distinctive ridged seeds found also in E. ciliatum, and looks quite similar to that species; both also have the AA chromosomal arrangement. However, it differs from E. ciliatum in being generally glabrous and glaucous, and by having exserted 4-lobed stigmas. W. Trelease (1891) and later P. A. Munz (1965) considered E. oreganum to be of hybrid origin, the presumptive parents being E. glaberrimum (glabrous) and so called E. adenocaulon (= E. ciliatum; ridged seeds). Some specimens have notably reduced seed set; whether that is the result of a hybrid origin, a failure to outcross in a plant with a very exserted stigma, or to another cause is not clear. The exact affinities of E. oreganum are uncertain, but it occupies a restricted and distinctive ecogeographical range and has a unique combination of morphological features.


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