Bog willowherb, épilobe leptophylle

Epilobium densum Rafinesque var. nesophilum Fernald; E. nesophilum (Fernald) Fernald; E. oliganthum Michaux var. gracile Farwell; E. palustre Linnaeus var. gracile (Farwell) Dorn; E. squamatum Nuttall; E. tenellum Rafinesque

Herbs with threadlike, nearly leafless epigeous stolons term­inating in compact, fleshy turions 3–8 × 2–4 mm. Stems erect, simple to loosely clustered, terete, 15–95 cm, simple to well branched, densely strigillose, often mixed glandular puberulent on inflorescence, rarely with faint strigillose lines decurrent from margins of petioles. Leaves opposite proximally, usually alternate, rarely fasciculate distally, subsessile; blade linear to very narrowly elliptic or sublanceolate, 2–7.5 × 0.1–0.7 cm, usually longer than internodes, base rounded to subcuneate, margins subentire, 4–7 inconspicuous teeth per side, sometimes revolute, lateral veins inconspic­uous, apex obtuse proximally to acute distally, both surfaces densely strigillose, increasing distally; bracts not much reduced. Inflorescences erect racemes, densely strigillose, often mixed sparsely glandular puberulent. Flowers erect; buds 3–5 × 1.5–2.5 mm; pedicel 5–12 mm; floral tube 0.8–1.5 × 1.2–1.8 mm, ring of spreading hairs at mouth inside; sepals 2.5–4.5 × 0.9–1.3 mm, abaxial surface strigillose; petals obcor­date, white to light pink, 3.5–7 × 1.6–4 mm, apical notch 1–1.8 mm; filaments white or cream, those of longer stamens 0.8–3.5 mm, those of shorter ones 0.6–2.5 mm; anthers cream, 0.5–0.9 × 0.4–0.6 mm; ovary 12–18 mm, densely strigillose, sometimes mixed glandular puberulent; style cream, 2–3.8 mm, stigma narrowly clavate, entire, 1–1.8 × 0.5–1.2 mm, usually surrounded by, rarely exserted beyond, anthers. Capsules straight, narrowly cylindrical, 35–80 mm, surfaces densely strigillose; pedicel 10–35 mm. Seeds narrowly fusiform to narrowly obovoid, 1.5–2.2 ×0.5–0.7 mm, chalazal collar 0.1–0.2 mm, ± pro­nounced, surface papillose; coma persistent, dingy white, 6–8 mm. 2n = 36.

Flowering Jun–Sep. Marshy ground, bogs, fens, low thickets, seepage areas, damp pastures; 0–1000(–2900) m; St. Pierre and Miquelon; Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.W.T., N.S., Ont., P.E.I., Que., Sask.; Alaska, Calif., Colo., Conn., Idaho, Ill., Ind., Iowa, Kans., Ky., Maine, Md., Mass., Mich., Minn., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.

The range of Epilobium leptophyllum overlaps with that of the related E. palustre, but the former is less common to the north and more common south into the midwestern United States, and absent only from most of the southern tier of states. It is also relatively uncommon in the western United States and Canada. Judging by the number of herbarium sheets that also include E. palustre, E. densum, and even E. coloratum, it sometimes occurs in sympatry with those species and may rarely hybridize with them, based on plants with intermediate morphology and/or sterile fruits.

Fernald described Epilobium nesophilum from the Magdalen Islands (Quebec), and especially Newfoundland, first as a variety of E. densum (1918), then as a separate species (1925).

Epilobium rosmarinifolium Pursh 1813, an illegit­imate name (not Haenke 1788), pertains here.