27. Epilobium parviflorum Schreber, Spic. Fl. Lips. 146, . 1771.
Smaller hairy willowherb
Herbs often robust and rank, with short-stalked leafy basal rosettes. Stems erect, terete, 18–100(–160) cm, well branched distally, densely gray-villous proximally, mixed villous and glandular puberulent distally, often with raised strigillose lines decurrent from margins of petioles. Leaves opposite proximal to inflorescence, alternate distally, petioles 1–3 mm proximally, sessile distally; blade narrowly lanceolate or oblong-lanceolate, 3–12 × 0.5–2.5 cm, often exceeding internodes, base rounded to broadly cuneate, margins serrulate, with 15–60 teeth per side, veins 4–8 per side, apex subacute, surfaces ± densely villous, hairs sometimes appressed; bracts usually much reduced. Inflorescences erect racemes or often leafy panicles. Flowers erect; buds 3.5–5.5 × 1.8–3 mm; pedicel 3–10 mm; floral tube 1–1.9 × 1.3–2.5 mm, a ring of spreading hairs at mouth within, densely villous and glandular puberulent abaxially; sepals narrowly lanceolate, often keeled, 2.5–6 × 1–1.5 mm; petals usually pink to rose-purple, rarely white, broadly obovate, 4–8.5 × 3–4.5 mm, apical notch 1–4 mm; filaments cream to light purple, those of longer stamens 2–6 mm, those of shorter ones 1–3.5 mm; anthers oblong, 0.8–1.3 × 0.4–0.6 mm; ovary 10–30 mm, mixed villous and glandular puberulent; style white to pink, 2.2–6 mm, glabrous, stigma deeply 4-lobed, 1–1.5 × 2.2–4 mm, lobes 1–1.8 mm, initially erect, later recurved, surrounded by or barely exserted beyond anthers. Capsules 30–70 mm, surfaces usually glandular puberulent, often mixed villous, rarely glabrescent; pedicel 5–18 mm. Seeds obovoid, 0.8–1.1 × 0.4–0.5 mm, chalazal collar inconspicuous, brown, surface coarsely papillose; coma easily detached, dingy white, 5–9 mm. 2n = 36.
Flowering Jun–Sep. Disturbed, wet areas near streams, bogs, rivers, and lakes, often calcareous; 0–150[–1800] m; introduced; B.C., Ont.; Mich., N.J., N.Y., Ohio, Pa., Vt., Wash.; Eurasia; n Africa; introduced also in Pacific Islands (New Zealand).
Epilobium parviflorum is widespread in Eurasia, from Europe through the Caucasus and southern Asia to eastern China (Chen C. J. et al. 1992), and in northwestern Africa and the Canary Islands (P. H. Raven 1967). Prior to the report of naturalized populations of E. parviflorum in Ontario by N. J. Purcell (1976), the species was considered an ephemeral adventive in New Jersey, New York, and Pennsylvania, where collections were made on ballast heaps in 1877–1880 (W. Trelease 1891; H. A. Gleason 1952, vol. 2) but not subsequently. However, recent collections indicate well-established populations scattered widely across the Great Lakes region (Purcell; E. G. Voss 1972–1996, vol. 2; T. S. Cooperrider and B. K. Andreas 1991) and more recently in the Pacific Northwest. Epilobium parviflorum is clearly naturalized and can be expected to spread farther, given its weedy nature (Raven and T. E. Raven 1976).
Epilobium parviflorum most closely resembles E. hirsutum, sharing the otherwise unique combination of densely villous pubescence and 4-lobed stigmas, but differs by having smaller flowers, leaves not clasping and/or decurrent on stems, and perennating by rosettes rather than by thick ropy stolons. The two species co-occur throughout most of their range in Eurasia, and although their adventive ranges in North America are quite similar, E. hirsutum has spread much more widely and rapidly.