Siskiyou willowherb

Epilobium obcordatum A. Gray subsp. siskiyouense Munz in N. L. Britton et al., N. Amer. Fl., ser. 2, 5: 205. 1965; E. obcordatum var. laxum Dempster

Herbs ± suffruticose, shoots from woody caudex with bark­like periderm extending to 40 cm below ground, shoots with scaly bases. Stems several to many, erect to ascend­ing, loosely clumped, terete, 10–25 cm, rarely branched distal to base, usually short-villous and strigillose throughout, mixed sparsely glandular puberulent dis­tally, rarely subglabrous proximal to inflorescence. Leaves opposite proximal to inflorescence, alternate and usually crowded distally, sessile; blade gray-green, narrowly to broadly ovate, 1.3–2.6 × 0.8–2 cm, base rounded to subcordate, margins usually serrulate, 6–12 teeth per side, rarely subentire, veins inconspicuous, 3–5 per side, apex rounded proximally to acute distally, surfaces sparsely short-villous to subglabrous and glaucous; bracts much reduced. Inflorescences erect, compact racemes, densely canescent and glandular puberulent, or subglabrous, only ovaries pubescent. Flowers erect; buds often purplish green, 9–11 × 3.5–5 mm, blunt; pedicel 6–12 mm; floral tube 2.1–4 × 2.9–5 mm, prominent ring of tissue 0.3–0.6 mm wide, edged by spreading hairs, 0.9–1.8 mm from base of tube inside; sepals purplish green, 5–10.5 × 2–3.5 mm, apex acute; petals pink to rose-purple, obcordate, 10–22.5 × 9.5–15.5 mm, apical notch 2–6.5 mm; filaments cream, those of longer stamens 6.5–14 mm, those of shorter ones 3.5–11 mm; anthers cream 1.9–3.3 × 0.7–1.2 mm; ovary 12–22 mm, ± densely canescent and glandular puberulent; style white to light pink, 10.5–18 mm, sparsely villous just proximal to stigma, stigma broadly 4-lobed, 1–1.8 × 2.4–4.2 mm, exserted beyond anthers. Capsules 25–45 mm, surfaces canescent and glandular puber­ulent; pedicel 6–25 mm. Seeds narrowly obovoid, 1.4–1.9 × 0.6–0.7 mm, with low, obscure chalazal collar, light brown, surface papillose; coma easily detached, somewhat tawny, 4–8 mm. 2n = 36.

Flowering Jul–Aug. Stream banks, moist, rocky slopes, montane ridges, sometimes on serpentine areas; 1600–2500 m; Calif., Oreg.

Epilobium siskiyouense is endemic to the Klamath region in southwestern Oregon (Jackson County) and north-central California in the Salmon, Scott Bar, and Siskiyou mountains of Siskiyou and Trinity counties. As noted by Hoch and Raven, this geographical range and several morphological features appear to be intermediate between those of E. obcordatum and E. rigidum. All three species have unusually large flowers (12–26 mm) with four-lobed stigmas, and as a group are quite distinct from their congeners in the region. Despite these similarities, the three taxa differ substantially in details of floral structure, especially regarding the dimensions of the floral tube. Specifically, E. rigidum has mean petal length 18.2 mm, floral tubes 1–1.6 × 2.5–3.6 mm; E. siskiyouense mean petal length 17.1 mm, floral tubes 2.1–4 × 2.9–5 mm; and E. obcordatum mean petal length 18.6 mm, floral tubes 3.2–5.2 × 2.2–3.6 mm. Thus, in flowers that are similar in overall size and aspect, E. rigidum has a very short, broad floral tube, E. obcordatum has a relatively long, narrow tube, and E. siskiyouense has a tube intermediate in size and shape. In terms of the ratio of tube length to width, the three taxa do not overlap. Although these characters are difficult to include in a key (since they require floral dissection and/or precise measure­ments), they are diagnostic for these species.

Epilobium siskiyouense has an additional diagnostic floral character that is unique in the genus. Whereas most other species of Epilobium have a simple ring of spreading hairs, sometimes with a low ridge of tissue near the mouth of the floral tube, E. siskiyouense has a relatively broad ring of tissue (0.3–0.6 mm wide), shaped like a washer, from which spreading hairs arise; this feature may provide protection for the nectar.

Epilobium siskiyouense has two distinct patterns of vestiture on the stems. In some specimens, the lower stems are mixed canescent and glandular puberulent and the inflorescence only glandular puberulent. In other specimens, the stems are subglabrous below a sparsely canescent and glandular puberulent inflorescence. There is no obvious correlation of this difference with any other morphological, ecological, or geographical factors.