19. Epilobium densum Rafinesque, Précis Découv. Somiol. 42. 1814.
Downy willowherb, épilobe dressé
Epilobium strictum Muhlenberg ex Sprengel
Herbs with threadlike, sparsely leaved epigeous stolons terminating with compact fleshy turions 4–8 × 3–4 mm. Stems erect, simple or loosely clustered, terete, 15–95 cm, often well branched distally, densely villous throughout, sometimes mixed glandular puberulent distally, decurrent lines absent. Leaves opposite proximally, alternate and often fasciculate distally, subsessile; blade oblong-lanceolate to sublinear, 2–4.5 × 0.3–0.9 cm, ± exceeding internodes, base cuneate, margins entire or denticulate, 3–6 inconspicuous teeth per side, sometimes revolute, veins apparent on abaxial side, 3–5 per side, apex acute, surfaces villous, especially distally; bracts somewhat reduced. Inflorescences erect racemes, branched or not, densely villous, sometimes mixed glandular puberulent. Flowers erect; buds 2.5–5 × 1.5–1.5 mm; pedicel 3–8 mm; floral tube 1–1.8 ×1–2 mm, ring of spreading hairs at mouth inside; sepals 2–4.5 × 1–1.3 mm, abaxial surface villous and glandular puberulent; petals light to dark pink, obcordate, 4–6 × 2–3 mm, apical notch 1–1.5 mm; filaments pink, those of longer stamens 2–3.5 mm, those of shorter ones 1–2 mm; anthers cream, 0.5–0.8 × 0.4–0.6 mm; ovary 12–20 mm, densely villous, often mixed glandular puberulent; style cream, 2–3.5 mm, stigma narrowly clavate, entire, 1–1.6 × 0.5–1 mm, surrounded by anthers. Capsules 35–68 mm, short-beaked, surfaces densely villous, sometimes mixed glandular puberulent; pedicel 5–15 mm. Seeds narrowly fusiform to narrowly obovoid, 1.5–2 × 0.5–0.6 mm, chalazal collar inconspicuous, 0.1 mm, surface low papillose; coma persistent, dingy white, 6–8 mm. 2n = 36.
Flowering Jul–Sep. Sphagnum and peat bogs, marshes, seeps, damp pastures; 0–600 m; N.B., N.S., Ont., P.E.I., Que.; Conn., Ill., Ind., Iowa, Maine, Md., Mass., Mich., Minn., N.H., N.J., N.Y., Ohio, Pa., R.I., Vt., Va., Wis.
Epilobium densum is relatively uncommon but widely distributed within the Great Lakes-St. Lawrence River region in boggy or marshy areas. Within that region, it sometimes grows in close proximity with E. leptophyllum and E. palustre; it is densely pubescent like E. leptophyllum, and although the type of hairs differs markedly on the two species, they sometimes are found mixed on herbarium sheets. Because it is less pubescent, E. palustre is rarely mixed or confused with E. densum. Hybrids among these species occur but are uncommon and generally marked by slightly to moderately reduced seed fertility.
M. L. Fernald (1944d), among others, argued that names published in the Catalogus by Muhlenberg were not validly published. In the case of Epilobium strictum, K. Sprengel considered that Muhlenberg provided enough of a description (upright, soft) to validate the name in 1825. However, Rafinesque had validly published the name E. densum for the same taxon in 1814.
Epilobium molle Torrey is an illegitimate name that pertains here.