Flora of North America species comparison

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Epilobium anagallidifolium

Epilobium oregonense

alpine willow-herb, pimpernel willow-herb, épilobe à feuilles de mouron

Oregon willowherb, slim-stem willowweed
Habit Herbs with spreading thin, small-leafed epigeous soboles to 5 cm. Herbs with slender stolons to 18 cm with minute, rounded leaves.
Stems

many, ascending, often sigmoidally bent, nodding distally, later erect, clumped or mat-forming, terete, 3–20(–25) cm, simple, subglabrous, sometimes with faint raised strigillose lines decurrent from margins of petioles, rarely mixed strigillose and sparsely glandular puberulent distally.

erect or ascending, often loosely matted, often flushed purple distally, terete, 8–30(–40) cm, simple or sparsely branched from base, subglabrous.
Leaves

opposite and crowded proximal to inflorescence, alternate distally, petioles 1–6 mm, rarely subsessile distally;

blade spatulate to oblong proximally, elliptic to narrowly lanceolate or sublinear distally, (0.5–)0.8–2.5 × 0.3–1 cm, base attenuate to cuneate, margins subentire proximally, sparsely denticulate distally with 2–5 low teeth per side, veins obscure, 2–4 per side, apex obtuse or rounded proximally to subacute distally, surfaces subglabrous;

bracts reduced, usually much narrower.

opposite proximal to inflorescence, alternate distally, subsessile;

blade broadly elliptic proximally, narrowly elliptic or lanceolate to sublinear distally, 5–25 × 1–7 mm, longer than internodes proximally to much shorter distally, base cuneate to rounded, margins subentire, veins extremely faint, 3–5 per side, apex obtuse, surfaces subglabrous;

bracts extremely reduced and linear.
Inflorescences

nodding in bud, later suberect, few-flowered racemes, subglabrous to sparsely strigillose and/or glandular puberulent.

usually erect, sometimes nodding in bud, racemes, open, unbranched, sparsely strigillose and glandular puberulent.
Flowers

suberect;

buds 2–5 × 1–2 mm;

pedicel 1–6(–15) mm;

floral tube 0.6–1.2 × 0.8–1.8 mm, slightly raised subglabrous ring at mouth inside;

sepals green to reddish purple, 1.5–5 × 0.6–1.5 mm, abaxial surface subglabrous to sparsely glandular;

petals usually pink to rose-purple, rarely white, narrowly obcordate, (1.7–)2.5–6.5(–8) × 1.6–3.5 mm, apical notch 0.5–1.2 mm;

filaments cream to light pink, those of longer stamens 1.4–3.2 mm, those of shorter ones 0.7–2 mm;

anthers 0.3–0.6 × 0.2–0.4 mm;

ovary often reddish purple, 6–20 mm, subglabrous or sparsely strigillose and glandular puberulent;

style white, 1.2–2.5 mm, glabrous, stigma broadly clavate to subcapitate, entire, 0.9–1.5 × 0.4–0.7 mm, surrounded by longer anthers.

suberect or nodding;

buds 2–3.5 × 1–1.5 mm, apex blunt;

pedicel 2–7 mm;

floral tube 0.8–1.8 × 1–2.1 mm, with faint ring of hairs at mouth inside;

sepals often flushed purple, 2.5–4.5 × 1–1.6 mm;

petals white to pink, 5–8 × 2.8–4 mm, apical notch 0.8–1.5 mm;

filaments white, those of longer stamens 2.8–4.5 mm, those of shorter ones 2–3.8 mm;

anthers yellow-cream, 0.8–1.2 × 0.4–0.5 mm;

ovary green to purple, 8–14 mm, sparsely strigillose and glandular puberulent;

style white, 3.8–4.8 mm, glabrous, stigma subcapitate, 1–1.4 × 1–1.2 mm, surrounded by longer anthers.
Capsules

slender, often reddish purple, 17–40(–55) mm, surfaces subglabrous or with scattered hairs;

pedicel 5–35(–68) mm.

slender, often purplish green, 21–40(–52) mm, surfaces subglabrous;

pedicel 20–65 mm.
Seeds

narrowly obovoid, 0.7–1.4 × 0.3–0.5 mm, inconspicuous chalazal collar 0.1–0.2 mm wide, light brown, surface reticulate (smooth);

coma persistent, dull white, 2–4 mm.

narrowlyoblanceoloid or subfusiform, 1–1.4 × 0.4–0.6 mm, chalazal collar 0.1–0.2 mm, light brown, surface low papillose;

coma persistent, whitish, 3–4 mm.
2n

= 36.

= 36.

Epilobium anagallidifolium

Epilobium oregonense
Phenology Flowering Jun–Sep. Flowering Jul–Aug.
Habitat Moist flats, stream banks, subarctic coastal marsh edges, high montane and alpine meadows and seeps. Montane to subalpine boggy or mossy areas, wet meadows, protected, semi-shaded stream banks.
Elevation 0–4500 m. [0–14800 ft.] 1200–3000(–3500) m. [3900–9800(–11500) ft.]
Distribution
from FNA
AK; CA; CO; ID; ME; MT; NH; NV; OR; UT; WA; WY; AB; BC; NL; NT; NU; QC; YT; Greenland; Eurasia
[WildflowerSearch map]
[BONAP county map]
from FNA
AZ; CA; CO; ID; MT; NM; NV; OR; UT; WA; WY; BC
[WildflowerSearch map]
[BONAP county map]
Discussion

Epilobium anagallidifolium is widely but sparsely distributed in high montane-alpine and subarctic Eurasia, including Europe, Russia, China, and Japan.

Epilobium anagallidifolium usually forms low clumps or mats, with stems nodding in bud and usually subglabrous below the inflorescence. Many collections of E. anagallidifolium from eastern Canada and Greenland tend to be unusually tall (to 25 cm) and robust for the species, with somewhat larger, thicker leaves, and longer pedicels (to 60 mm). Similarly large and robust specimens occur scattered in Yukon and Washington, and may result from occasional hybridization and introgression with sympatric species such as E. hornemannii or E. lactiflorum, which also have the CC chromosomal arrangement. In an analysis of Fennoscandian populations of the Alpinae group, I. Kytövuori (1972) found a similar pattern of mostly smaller, sigmoidal plants of E. anagallidifolium with a small proportion of larger ones, and he also suggested the possibility of hybridization and/or introgression.

Plants of Epilobium anagallidifolium, and indeed of the whole Alpinae group, from Haida Gwaii (the Queen Charlotte Islands) of British Columbia (J. A. Calder and R. L. Taylor 1968), are particularly distinctive compared to those on the mainland, and difficult to interpret. The observed differences may be the result of hybridization with other sympatric species or a response to unique ecological conditions on the islands, reinforced by relative isolation from mainland British Columbia.

The Linnaean name Epilobium alpinum has long been a source of nomenclatural confusion and instability, since it circumscribed at least four distinct species, especially E. anagallidifolium. A proposal by P. C. Hoch et al. (1995) to permanently reject the name E. alpinum Linnaeus was approved.

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

Epilobium oregonense is a distinctive western North American endemic, found primarily throughout the Cascade–Sierra mountain complex barely into the Transverse Ranges of southern California, and very scattered through the Rocky Mountains. It is exceedingly rare in Arizona, Colorado, and New Mexico.

Even though Epilobium oregonense bears some similarity to E. anagallidifolium and other members of the Alpinae group, and often grows in close proximity to them, this species does not share the derived CC chromosomal arrangement with that group, instead having the more globally widespread BB arrangement. The similarities with E. anagallidifolium include the small stature, small, obtuse, and subentire leaves, and long pedicels in fruit; however, E. oregonense differs by its long, threadlike stolons, distal leaves extremely narrow and reduced in size relative to the internodes, and near complete absence of pubescence on the plant, including a lack of raised lines of hairs on the stems.

Another species with which Epilobium oregonense has been confused is E. hallianum, but that species always forms condensed basal turions, is more strictly erect, and generally has larger and more denticulate leaves. The distinctive and diagnostic stolons of E. oregonense are similar to those found in E. palustre and related species (all of which also have the BB chromosome arrangement), except that those of E. oregonense never terminate in a condensed turion, as found in those other species. The exact affinities of E. oregonense remain uncertain, but it appears to be most closely related to the E. palustre complex.

Some specimens of Epilobium oregonense grow as floating mats in cold streams; these specimens are notably large, with particularly strong development of basal stolons and larger, more lanceolate leaves. As evidenced by mixed herbarium collections, E. oregonense grows sympatrically with several congeners, including E. anagallidifolium, E. ciliatum subspp. ciliatum and glandulosum, E. hallianum, and E. hornemannii, and hybridizes occasionally, at least with E. ciliatum subsp. ciliatum and E. hornemannii.

Epilobium oregonense var. gracillimum Trelease, which pertains here, was not validly published, and other names based on it are also invalid.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Parent taxa Onagraceae > subfam. Onagroideae > tribe Epilobieae > Epilobium > sect. Epilobium Onagraceae > subfam. Onagroideae > tribe Epilobieae > Epilobium > sect. Epilobium
Sibling taxa
E. arcticum, E. brachycarpum, E. campestre, E. canum, E. ciliatum, E. clavatum, E. cleistogamum, E. coloratum, E. davuricum, E. densiflorum, E. densum, E. foliosum, E. glaberrimum, E. hallianum, E. hirsutum, E. hornemannii, E. howellii, E. lactiflorum, E. leptocarpum, E. leptophyllum, E. luteum, E. minutum, E. mirabile, E. montanum, E. nevadense, E. nivium, E. obcordatum, E. obscurum, E. oreganum, E. oregonense, E. pallidum, E. palustre, E. parviflorum, E. rigidum, E. saximontanum, E. septentrionale, E. siskiyouense, E. smithii, E. suffruticosum, E. torreyi
E. anagallidifolium, E. arcticum, E. brachycarpum, E. campestre, E. canum, E. ciliatum, E. clavatum, E. cleistogamum, E. coloratum, E. davuricum, E. densiflorum, E. densum, E. foliosum, E. glaberrimum, E. hallianum, E. hirsutum, E. hornemannii, E. howellii, E. lactiflorum, E. leptocarpum, E. leptophyllum, E. luteum, E. minutum, E. mirabile, E. montanum, E. nevadense, E. nivium, E. obcordatum, E. obscurum, E. oreganum, E. pallidum, E. palustre, E. parviflorum, E. rigidum, E. saximontanum, E. septentrionale, E. siskiyouense, E. smithii, E. suffruticosum, E. torreyi
Synonyms E. alpinum, E. pseudoscaposum
Name authority Lamarck in J. Lamarck et al.: Encycl. 2: 376. (1786) Haussknecht: Monogr. Epilobium, 276, plate 14, fig. 66. (1884)
Source FNA vol. 10. Treatment author: Peter C. Hoch. FNA vol. 10. Treatment author: Peter C. Hoch.
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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