Flora of North America species comparison

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.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Epilobium palustre is an extremely widespread circumboreal species that is relatively common from Alaska across Canada, especially around the Great Lakes to the Maritime provinces (mostly below 1000 m). This species is somewhat less common in the northeastern United States, and only scattered in the mountains of the western United States, south to California and Colorado (to 3000 m). It also occurs in ice-free regions of Greenland south of 70º north latitude, in northern and central Europe, across most of subarctic Russia to the Caucasus, the Himalaya complex, and eastern Asia, including Japan and the Russian Far East.

Epilobium palustre shows considerable variation across its very wide distribution and, not surprisingly, distinctive local races, which sometimes have been named formally, including several from northeastern North America. Within series Palustriformes by C. Haussknecht (1884), M. L. Fernald (1944d) clarified much confusion in names at that time, clearly delineating and establishing the nomenclature of E. davuricum, E. leptophyllum, E. palustre, and E. densum. Fernald also recognized E. nesophilum (see discussion under 18. E. leptophyllum) and E. pylaieanum, the latter based on small plants of E. palustre from southern Newfoundland.

Epilobium lineare Muhlenberg and E. palustre var. albiflorum Lehmann are illegitimate names that pertain here.

(Discussion copyrighted by Flora of North America; reprinted with permission.)