Med. Repos., hexade 2, 5: 361. 1808.
Herbs with leafy basal rosettes or large, fleshy, condensed underground turions, or sometimes shoots from caudex. Stems erect, green or tan to reddish green, terete, (3–)10–120(–190) cm, often thick, well branched or simple, subglabrous proximal to inflorescence with raised strigillose lines decurrent from margins of petioles, ± densely mixed strigillose and glandular puberulent distally, rarely densely strigillose or densely villous throughout. Leaves opposite proximal to inflorescence, alternate distally, petiole 0–5(–10) mm, often subsessile distally, sometimes clasping; blade narrowly obovate, obovate, broadly elliptic, or spatulate proximally, to very narrowly lanceolate to ovateor broadly elliptic distally, (1–)3–12(–16) × (0.2–)0.6–5.5 cm, base rounded to cuneate or short-attenuate, margins serrulate, (8–)15–40 irregular teeth per side, veins prominent, 4–10 per side, apex obtuse to acute or subacuminate, surfaces usually subglabrous with strigillose margins, rarely densely strigillose or villous; bracts scarcely reduced to very reduced and narrower. Inflorescences usually erect, rarely nodding, racemes or panicles, well branched and open, to simple and congested, ± densely strigillose and glandular puberulent. Flowers erect; buds 1.5–7 × 1–3 mm; pedicel 2–14(–20) mm; floral tube 0.5–2.6 × 0.9–3.5 mm, ring of spreading hairs at mouth inside; sepals often reddish green, lanceolate, sometimes keeled, 2–7.5 × 0.7–2.5 mm; petals white or pink to rose-purple, obovate, 2–14 × 1.3–6.3 mm, apical notch 0.4–2.5 mm; filaments white to dark pink, those of longer stamens 1.4–7 mm, those of shorter ones 0.6–5.2 mm; anthers light yellow to cream, 0.5–1.8 × 0.3–0.9 mm; ovary often reddish green, 8–40 mm, ± densely mixed strigillose and glandular pubescent; style cream to light yellow, 1.1–8.5 mm, stigma cream to orange-yellow, narrowly to broadly clavate or subcapitate, 0.8–2.8 × 0.4–1.2 mm, rarely indented apically, usually surrounded by, rarely exserted beyond, anthers. Capsules erect, (15–)30–100 mm, surfaces usually strigillose and glandular puberulent, rarely glabrescent; pedicel 2–15(–40) mm, rarely subsessile. Seeds narrowly obovoid or subfusiform, (0.6–)0.8–1.6(–1.9) × 0.3–0.6 mm, chalazal collar ± conspicuous, 0.1–0.3 × 0.2–0.4 mm, grayish tan to brown, surface with conspicuous parallel longitudinal ridges of laterally flattened papillae; coma readily detached, white or dingy white, 2–8 mm, very rarely absent. 2n = 36.
North America, Mexico, Central America, South America, e Asia, introduced in Europe, Pacific Islands, Australia.
Subspecies 3 (3 in the flora).
Epilobium ciliatum, which has the AA chromosomal arrangement, shows extraordinary variation in morphology. It has the largest geographical range among North American Epilobium species, and has spread invasively outside of its native range. Although almost certainly originating in North America, E. ciliatum is also considered native in South America (J. C. Solomon 1982) and East Asia (Chen C. J. et al. 1992), but adventive in Europe and western Russia (P. H. Raven 1968), Pacific Islands, especially New Zealand, and Australia (Raven and T. E. Raven 1976). Its chromosomal affinities and morphological similarities to a small group of species in western North America strongly suggest that that region is its center of origin.
Within the enormous variation displayed by Epilobium ciliatum, three broadly defined entities can be recognized: subsp. watsonii, characteristically with bracts scarcely reduced on an extended, crowded corymbose inflorescence, found only along the Pacific coast, usually within sight of the ocean; subsp. glandulosum, generally large, few-branched plants with condensed turions just below ground and crowded inflorescences of relatively large rose-purple flowers, found mainly in damp, cool, and relatively undisturbed habitats; and subsp. ciliatum, which range from small and simple to large and well-branched, usually with leafy basal rosettes and open inflorescences, relatively narrow leaves and small white flowers, found most often in disturbed damp to dry habitats throughout the entire range of the species. These subspecies often intergrade in regions where their ranges overlap, resulting in populations with diverse mixtures of intermediate characters, yet the subspecies consistently retain their main morphological characteristics in populations throughout most of their respective ranges. Each shows some degree of endogenous variability, most notably in the very widespread subsp. ciliatum.
|1||Leaf blades very narrowly lanceolate to narrowly ovate or elliptic, proximally narrowly obovate to spatulate; bracts very reduced on open inflorescence; petals 2–6(–9) mm, white or sometimes pink; herbs usually with rosettes, rarely fleshy turions.||Epilobium ciliatum subsp. ciliatum|
|1||Leaf blades narrowly ovate to ovate to broadly elliptic, sometimes lanceolate, proximally obovate to broadly elliptic; bracts little reduced on crowded inflorescence; petals 4.5–12(–15) mm, usually rose-purple to pink, rarely white; herbs usually with fleshy turions or rosettes, rarely fleshy shoots.||> 2|
|2||Herbs usually with large, condensed subsessile turions 1–10 cm below ground, leaving dark scales, rarely with rosettes of fleshy leaves; inflorescences simple or branched, not corymbose.||Epilobium ciliatum subsp. glandulosum|
|2||Herbs with leafy basal rosettes, sometimes fleshy shoots from woody caudex; inflorescences ± simple, subcorymbose.||Epilobium ciliatum subsp. watsonii|