Snow Mountain willowherb

Herbs with many shoots from thick, woody caudex 5–12 mm diam.. Stems erect or ascending, terete, 10–25 cm, sparsely branched distally, densely grayish white-strigillose. Leaves subsessile or petioles 0.5–2.5 mm, blade elliptic or narrowly so to lanceolate, often folded along midrib, 0.9–1.8 × 0.3–0.7 cm, usually longer than internodes, base rounded to cuneate, margins subentire or low denticulate, 1–3 low teeth per side, lateral veins inconspicuous, 1–3 per side, apex blunt to acute with conspicuous dark brown mucronate tip, surfaces densely spreading-hairy; bracts very reduced, attached to pedicel 1–2 mm from base. Inflorescences erect open racemes or panicles, densely spreading-hairy. Flowers erect; buds 6–8 × 2.5–3.2 mm; floral tube 5.2–9.5 × 2.4–3.2 mm, constriction 4–6 mm distal to base, base ± bulbous, spreading-hairy from mouth nearly to base inside; sepals 2.7–4.2 × 1.6–2 mm, abaxial surface densely villous and glandular puberulent; petals rose-purple, 6–9.5 ×3.8–6.2 mm, apical notch 1.5–2.5 mm; filaments light pink, those of longer stamens 5–6.5 mm, those of shorter ones 3–3.5 mm; anthers 1.3–2.1 × 0.6–0.9 mm, apicu­late; ovary 2.5–4.5 mm, densely villous and glandular puberulent; style pinkish cream, 11–17 mm, glabrous, stigma 4-lobed, 0.8–1 × 1.1–2.1 mm, lobes often not spread and then cuplike, usually exserted beyond anthers. Capsules fusiform, 8–16 mm, surfaces glandular puberulent; pedicel 2–5 mm. Seeds obovoid to broadly so, with slight constriction 0.4–0.6 mm from micropylar end, 1.5–2.4 × 0.8–1.3 mm, inconspicuous chalazal collar, dark brown, surface papillose; coma easily detached, dingy white, 6.5–7.5 mm. 2n = 30.

Flowering late Jul–Sep. Crevices in rocky outcrops, shale or talus slopes, with scrub oak (Quercus), Abies concolor, and Pinus jeffreyi; 1600–2400 m; Calif.

Epilobium nivium has an extremely restricted range, mainly in the Snow Mountain region of Colusa and Lake counties, but recent collections from Mendocino and southern Trinity counties have extended its range several hundred km to the north. Many collections, notably including the type gathering, have strikingly woody bases, suggesting that these are long-lived plants. Like E. nevadense and some other species in the genus that characteristically grow on scree slopes, the lower part of the stems often lack leaves, which may be abraded by movement of the rocky substrate.

As reported by S. R. Seavey and P. H. Raven (1977c) and also noted on some herbarium labels, capsules of Epilobium nivium sometimes show signs of possible seed predation by moth larvae as reported for E. nevadense.