Dahurian willowherb, épilobe de Daourie

Epilobium palustre Linnaeus var. davuricum (Fischer ex Sprengel) S. L. Welsh

Herbs with basal rosettes of linear leaves 12–40 × 2–5 mm. Stems erect, rarely clumped, terete, 10–40(–45) cm, usually simple, rarely branched, glabrous proxi­mal to inflorescence with sparsely strigillose raised lines decurrent from margins of petioles, mixed strigillose and glandular puberulent distally. Leaves opposite and crowded proximal to inflorescence, alternate and scattered distally, sub­sessile; blade narrowly oblong or narrowly lanceolate to linear, (1.2–)2–4.5 × 0.1–0.5 cm, base attenuate, margins irregularly denticulate, 2–4 teeth per side, veins inconspicuous, 3 or 4 per side, apex subacute to obtuse or ± truncate, surfaces glabrous with sparsely strigillose margins and adaxial midrib; bracts much reduced and narrower. Inflorescences nodding in bud, suberect later, racemes, simple, mixed strigillose and glandular puberulent, sometimes subglabrous. Flowers erect, sometimes starting in third most-proximal node; buds 3–6.5 × 1–2 mm; pedicel 4–15 mm; floral tube 0.7–1.6 × 1–2.2 mm, with or often without ring of spreading hairs at mouth inside; sepals 1.2–3.5 × 0.7–1.2 mm, apex subacute; petals white, 2–5.5 × 1.2–3.1 mm, apical notch 0.3–1 mm; filaments white or cream, those of longer stamens 1–2.5 mm, those of shorter ones 0.5–1.4 mm; anthers cream, 0.4–0.6 × 0.3–0.5 mm; ovary usually purplish red, 10–20 mm, sparsely mixed strigillose and glandular puberulent or subglabrous; style cream or white, 0.7–2.5 mm, stigma cylindrical to clavate, entire, 0.8–2 × 0.2–1.2 mm, surrounded by anthers. Capsules slender, 30–55 mm, surfaces sparsely strigillose and glandular puberulent; pedicel 8–38 mm. Seeds narrowly attenuate, 1.4–2 × 0.3–0.5 mm, chalazal collar conspicuous, 0.1–0.3 mm, light brown or blond, surface papillose; coma persistent, white, 3–5 mm. 2n = 36.

Flowering Jul–Aug. Subarctic open balsam poplar and spruce forests, taiga, wet meadows, boggy coastal areas, limestone barrens, wet marly soils; 0–1500(–2000) m; Alta., B.C., Man., Nfld. and Labr. (Nfld.), N.W.T., Nunavut, Ont., Que., Sask., Yukon; Alaska; Europe (Russia).

Even though Epilobium davuricum has not yet been characterized by chromosome group, its morphology and general distribution suggest that it (plus E. arcticum) is related to E. palustre as a member of the Palustriformes group. It does not have the turion-tipped stolons that characterize E. palustre and relatives but has similarly large seeds with a distinct chalazal collar. Some specimens with aberrant combinations of characters suggest that E. davuricum may hybridize with E. palustre and possibly E. arcticum in areas where their distributions overlap.