American Willowherb

This variable taxon, which probably originated in North America, has become the most widespread and abundant species of Epilobium worldwide. Epilobium ciliatum subsp. glandulosum (Lehmann) Hoch & P. H. Raven occurs throughout montane and boreal North America; E. ciliatum subsp. watsonii (Barbey) Hoch & P. H. Raven occurs along the North American Pacific shoreline from C California to British Columbia.

Herbs perennial, erect, with compact leafy rosettes or rarely fleshy turions that leave brown basal scales. Stems (10-)25-90(-150) cm tall, well-branched or rarely simple, strigillose and glandular pubescent, sparsely pubescent or glabrescent below, with raised strigillose lines decurrent from margins of petioles. Leaves sessile above, lower ones with petioles 1-3 mm; cauline blade lanceolate to narrowly ovate, 2.5-6(-7) × 0.6-1.5(-2) cm, subglabrous except for strigillose margin and veins, base rounded or rarely subcordate, margin serrulate with 10-30 teeth per side, apex acute to subacuminate. Inflorescence and flowers erect. Sepals 2.4-3.5 mm, keeled. Petals pink or white, rarely rose-purple, 3.5-5(-7) mm. Stigma clavate to cylindric, entire. Capsules 4.5-7 cm, sparsely strigillose and glandular; pedicels 0.5-0.8(-1.4) cm. Seeds brown, 0.8-1.2 mm, with conspicuous longitudinal ridges of flattened, fused papillae, with chalazal collar 0.08-0.1 mm; coma dull white, readily detaching. Fl. Jul-Aug(-Sep), fr. Aug-Oct. 2n = 36.

Heilongjiang, Jilin [Japan, Korea, Russia (Far East); extremely widespread in North and South America; naturalized in Asia, Australia, Europe, and New Zealand].

Moist disturbed places along streams, rivers, roadside ditches, slopes, and seeps; (700-)1200-2100 m.

Epilobium glandulosum Lehmann var. asiaticum H. Hara; E. glandulosum var. kurilense (Nakai) H. Hara; E. kurilense Nakai; E. maximowiczii Haussknecht; E. punctatum H. Léveillé.