Flora of North America species comparison

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Epilobium oregonense

Epilobium nivium

Oregon willowherb, slim-stem willowweed

Snow Mountain willowherb
Habit Herbs with slender stolons to 18 cm with minute, rounded leaves. Herbs with many shoots from thick, woody caudex 5–12 mm diam..
Stems

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

erect or ascending, terete, 10–25 cm, sparsely branched distally, densely grayish white-strigillose.
Leaves

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.

subsessile or petioles 0.5–2.5 mm, blade elliptic or narrowly so to lanceolate, often folded along midrib, 0.9–1.8 × 0.3–0.7 cm, usually longer than internodes, base rounded to cuneate, margins subentire or low denticulate, 1–3 low teeth per side, lateral veins inconspicuous, 1–3 per side, apex blunt to acute with conspicuous dark brown mucronate tip, surfaces densely spreading-hairy;

bracts very reduced, attached to pedicel 1–2 mm from base.
Inflorescences

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

erect open racemes or panicles, densely spreading-hairy.
Flowers

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.

erect;

buds 6–8 × 2.5–3.2 mm;

floral tube 5.2–9.5 × 2.4–3.2 mm, constriction 4–6 mm distal to base, base ± bulbous, spreading-hairy from mouth nearly to base inside;

sepals 2.7–4.2 × 1.6–2 mm, abaxial surface densely villous and glandular puberulent;

petals rose-purple, 6–9.5 ×3.8–6.2 mm, apical notch 1.5–2.5 mm;

filaments light pink, those of longer stamens 5–6.5 mm, those of shorter ones 3–3.5 mm;

anthers 1.3–2.1 × 0.6–0.9 mm, apiculate;

ovary 2.5–4.5 mm, densely villous and glandular puberulent;

style pinkish cream, 11–17 mm, glabrous, stigma 4-lobed, 0.8–1 × 1.1–2.1 mm, lobes often not spread and then cuplike, usually exserted beyond anthers.
Capsules

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

pedicel 20–65 mm.

fusiform, 8–16 mm, surfaces glandular puberulent;

pedicel 2–5 mm.
Seeds

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.

obovoid to broadly so, with slight constriction 0.4–0.6 mm from micropylar end, 1.5–2.4 × 0.8–1.3 mm, inconspicuous chalazal collar, dark brown, surface papillose;

coma easily detached, dingy white, 6.5–7.5 mm.
2n

= 36.

= 30.

Epilobium oregonense

Epilobium nivium
Phenology Flowering Jul–Aug. Flowering late Jul–Sep.
Habitat Montane to subalpine boggy or mossy areas, wet meadows, protected, semi-shaded stream banks. Crevices in rocky outcrops, shale or talus slopes, with scrub oak (Quercus), Abies concolor, and Pinus jeffreyi.
Elevation 1200–3000(–3500) m. (3900–9800(–11500) ft.) 1600–2400 m. (5200–7900 ft.)
Distribution
from FNA
AZ; CA; CO; ID; MT; NM; NV; OR; UT; WA; WY; BC
[WildflowerSearch map]
[BONAP county map]
from FNA
CA
[BONAP county map]
Discussion

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.)

Epilobium nivium has an extremely restricted range, mainly in the Snow Mountain region of Colusa and Lake counties, but recent collections from Mendocino and southern Trinity counties have extended its range several hundred km to the north. Many collections, notably including the type gathering, have strikingly woody bases, suggesting that these are long-lived plants. Like E. nevadense and some other species in the genus that characteristically grow on scree slopes, the lower part of the stems often lack leaves, which may be abraded by movement of the rocky substrate.

As reported by S. R. Seavey and P. H. Raven (1977c) and also noted on some herbarium labels, capsules of Epilobium nivium sometimes show signs of possible seed predation by moth larvae as reported for E. nevadense.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 10. FNA vol. 10.
Parent taxa Onagraceae > subfam. Onagroideae > tribe Epilobieae > Epilobium > sect. Epilobium Onagraceae > subfam. Onagroideae > tribe Epilobieae > Epilobium > sect. Cordylophorum > subsect. Petrolobium
Sibling taxa
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
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. 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
Name authority Haussknecht: Monogr. Epilobium, 276, plate 14, fig. 66. (1884) Brandegee: Zoë 3: 242, plate 24. (1892)
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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