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

25. Epilobium obscurum Schreber, Spic. Fl. Lips. 147, [155]. 1771.

Dwarf willowherb

Herbs with elongated, leafy epigeal stolons. Stems erect or ascending, subterete, 20–80 cm, often well branched from base, sometimes also distally, sub­glabrous proximal to inflo­rescence with raised strigillose lines decurrent from margins of petioles, strigillose distally. Leaves opposite proximal to inflorescence, alternate distally, petiole 0–2 mm; blade green or slightly bluish green, lanceolate to narrowly ovate, 1.5–10 × 0.4–1.8 cm, ± shorter than internodes, base rounded to atten­uate, margins denticulate with 15–40 evenly spaced teeth per side, veins prominent, 3–7 per side, apex sub­acute, surfaces sparsely strigillose, mainly on margins and veins; bracts gradually reduced. Inflorescences erect racemes or sparse panicles, strigillose. Flowers erect; buds 2–5 × 1–2.5 mm; pedicel 2–14 mm; floral tube 0.8–1 × 1.1–1.5 mm, conspicuous ring of spreading hairs at mouth inside, mixed strigillose and sparse glandular puberulent externally; sepals lanceolate, somewhat keeled, 2.5–4 × 1–1.3 mm, abaxial surface strigillose; petals rose-purple, 3.5–6 × 1.8–3 mm, apical notch 0.8–1.4 mm; filaments pale pink, those of longer stamens 2–2.2 mm, those of shorter ones 0.8–1.3 mm; anthers yellow, 0.7–0.8 × 0.4–0.5 mm; ovary 12–38 mm, strigillose; style white, 2.5–3.5 mm, glabrous, stigma clavate, 1.5–2 × 0.6–0.8 mm, surrounded by longer anthers. Capsules 40–70 mm, surfaces strigillose; pedicel 4–16 mm. Seeds narrowly obovoid, 0.9–1 × 0.3–0.4 mm, chalazal collar inconspicuous, brown, surface coarsely papillose; coma readily detached, dull white, 4–5 mm. 2n = 36.

Flowering Jul–Aug. Ruderal areas, banks of ditches, streams, edges of swampy areas; 0–200[–500] m; introduced; B.C.; Mich., Wash.; Europe; introduced also in South America (Chile), Africa (Morocco), Pacific Islands (New Zealand), Australia (Tasmania).

Epilobium obscurum, native throughout Europe and the European part of Russia except the far north, to Turkey and the Azores, is one of several Eurasian species that has naturalized in North America, follow­ing multiple early introductions around east coast port cities, and later around the Great Lakes. E. G. Voss (1972–1996, vol. 2) reported a collection of E. obscurum made in 1927 in Michigan near Detroit, but despite efforts by Voss and others, no additional collections of this species have been detected in that area, suggesting that it failed to become naturalized there.

In the Pacific Northwest, W. Suksdorf grew and collected at least six European taxa in his garden in Bingen (Klickitat County, Washington); this included E. obscurum (as early as 1922) but none of those taxa became naturalized. However, one or more independent new introductions in the Seattle (P. Zika, pers. comm.) and Vancouver (F. Lomer, pers. comm.) regions appear to be more persistent and the species should be considered naturalized there.


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