Epilobium torreyi

(S. Watson) Hoch & P. H. Raven

Phytologia 73: 458. 1993.

Common names: Torrey’s willowherb
Basionym: Oenothera torreyi S. Watson Proc. Amer. Acad. Arts 8: 600. 1873
Synonyms: Boisduvalia parviflora A. Heller B. stricta (A. Gray) Greene B. torreyi (S. Watson) S. Watson Gayophytum strictum A. Gray 1868 Oenothera densiflora var. tenella A. Gray
Treatment appears in FNA Volume 10.

Herbs with taproot. Stems erect, terete, (1–)4–65 cm, usually with several erect or ascending virgate branches proximally or simple, densely villous, sometimes mixed strigillose, or sometimes subglabrous. Leaves opposite only in proximal pairs, distally alternate, subsessile, blade linear-lanceolate to very narrowly elliptic, 0.5–4.5 × 0.2–0.3(–0.6) cm, usually longer than internodes, base cuneate, margins subentire to sparsely serrulate, 2–5 low teeth per side, lateral veins obscure, 2–5 per side, apex acute, surfaces subglabrous proximally to densely villous and/or strigillose distally; bracts slightly reduced. Inflorescences erect spikes, simple or sparsely branched, ± densely villous and/or strigillose. Flowers erect, often initiating in most proximal nodes, usually cleistoga­mous; buds 0.8–1.5 × 0.5–1 mm; floral tube 0.4–1 × 0.6–1.2 mm, ring of lax hairs near base inside; sepals 0.7–2 × 0.4–0.8 mm; petals pink with darker veins or white, 1.2–3.2 × 0.9–1.8 mm, apical notch 0.4–1 mm; filaments pale pink, those of longer stamens 0.4–1.8 mm, those of shorter ones 0.3–1 mm; anthers 0.3–0.6 × 0.3–0.4 mm, apiculate; ovary 3–6 mm, densely pubescent; style pale pink, 1.2–2.8 mm, stigma clavate to subcapitate or irregularly 4-lobed, 0.5–1.2 ×0.3–0.6 mm, surrounded by longer anthers. Capsules cylindrical to subfusiform, terete to slightly 4-angled, (6–)8–14 × 1.1–2 mm, beak 2–3 mm, central column disintegrating, villous; sessile. Seeds 3–6 per locule, irregularly angular-oblong or fusiform, 0.9–1.6 × 0.4–0.9 mm, chalazal collar absent, brown, surface irregularly reticulate. 2n = 18.

Phenology: Flowering May–Aug.
Habitat: Moist places along stream banks, seasonal streambeds, seeps, and roadside ditches, often in gravelly red or granite soil.
Elevation: 0–2600 m.


B.C., Calif., Idaho, Nev., Oreg., Wash.


Epilobium torreyi is an annual species that has a unique gametic chromosome number of n = 9, the lowest found in the genus. Its morphological similarity to Epilobium pallidum (n = 10) suggested to P. H. Raven and D. M. Moore (1965) that E. torreyi may be an aneuploid derivative of E. pallidum or a close relative.

No natural hybrids among species of sect. Pachydium have been reported, but in fact such plants might be difficult to detect. S. R. Seavey (1992) was able to form hybrids, but they were highly sterile. Nevertheless, hybridization between species with n = 9 and n = 10, followed by polyploidization, may well have given rise to the South American species of this section, Epilobium subdentatum (n = 19).

Selected References


Lower Taxa

... more about "Epilobium torreyi"
Peter C. Hoch +
(S. Watson) Hoch & P. H. Raven +
Oenothera torreyi +
Torrey’s willowherb +
B.C. +, Calif. +, Idaho +, Nev. +, Oreg. +  and Wash. +
0–2600 m. +
Moist places along stream banks, seasonal streambeds, seeps, and roadside ditches, often in gravelly red or granite soil. +
Flowering May–Aug. +
Boisduvalia parviflora +, B. stricta +, B. torreyi +, Gayophytum strictum +  and Oenothera densiflora var. tenella +
Epilobium torreyi +
Epilobium sect. Pachydium +
species +