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FNA | Family List | FNA Vol. 10 | Onagraceae | Epilobium

1. Epilobium rigidum Haussknecht, Oesterr. Bot. Z. 29: 51. 1879.

Stiff willowherb

Epilobium rigidum var. canescens Trelease

Herbs from woody caudex forming hypogeal shoots with barklike periderm. Stems several to many, suberect or ascending, terete, 10–40 cm, simple or sparsely branched, usually glabrous and ± glaucous proximal to inflorescence, strigillose distally, sometimes densely strigillose throughout. Leaves crowded distally, petiole 2–6 mm, blade narrowly ovate to ovate or broadly elliptic, often obovate in proximal pairs; cauline 2–4.5 × 0.8–2 cm, base rounded to attenuate, margins subentire or finely denticulate, 8–12 teeth per side, lateral veins inconspicuous, 3–5 per side, apex obtuse proximally to subacute distally, surfaces glaucous and subglabrous to densely strigillose; bracts narrower and much smaller. Inflorescences erect racemes, simple, ± densely strigillose, rarely mixed sparsely glandular puberulent. Flowers erect; buds 6–11 × 4–5 mm, apiculate; pedicels 4–8 mm; floral tube 1–1.8 × 2–3 mm, with raised ring of tissue edged with spreading hairs at mouth inside; sepals often reddish green, lanceolate, 9.5–14.5 × 2.5–3.5 mm, apex acuminate, abaxial surface densely strigillose; petals pink to rose-purple, obcordate, 16–20 × 13–16 mm, apical notch 3.4–5.5 mm; filaments light pink, those of longer stamens 9–14 mm, those of shorter ones 6.5–10 mm; anthers cream, 1.8–3.5 × 1–1.9 mm; ovary 6–12 mm, densely strigillose; style cream to light pink, 14.5–18.5 mm, stigma broadly 4-lobed, 1–1.5 × 3–3.5 mm, exserted beyond anthers. Capsules 20–35 mm, surfaces strigillose; pedicel 9–13 mm, bracts often attached 2–3 mm from base. Seeds narrowly obovoid, constriction 0.6–0.8 mm from micropylar end, 2.5–3.4 × 0.9–1.4 mm, chalazal collar obscure, light brown, surface papillose; coma easily detached, white, 6–8 mm. 2n = 36.

Flowering Jul–Sep. Dry rocky or sandy benches, rocky hillsides, dry streambeds in coniferous forests, on seasonally moist serpentine slopes, rarely along disturbed roadsides; 100–1200(–1500) m; Calif., Oreg.

Within its range in northwestern California and southwestern Oregon, Epilobium rigidum is restricted to unusually dry habitats compared to most species in sect. Epilobium, but is not unlike taxa in the non-n = 18 clade, which are both perennial and annual. It is self-compatible, but with strongly protandrous flowers and an exserted stigma, and is modally outcrossing, pollinated by bees and flies.

Plant vestiture varies from subglabrous to densely strigillose throughout (var. canescens), but plants with these differences can be in the same population, and no other morphological differences between them have been found.


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