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milk-flower willowherb, white-flower willow-herb, épilobe à fleurs blanches

California willowherb, chaparral willowherb, desert willowherb, little willowherb, minute willowherb, small-flower willowherb

Habit Herbs with short, leafy epigeal soboles. Herbs slender.
Stems

ascending to suberect, often clumped, terete, 15–50 cm, usually simple, rarely branched proximally, subglabrous proximal to inflorescence except for raised densely strigillose lines decurrent from margins of petioles, usually mixed strigillose and glandular puberulent distally.

strict, erect, sometimes reddish green, terete, 3.5–40 cm, simple or freely branched, subglabrous proximally to strigillose and glandular puberulent distally.

Leaves

opposite proximal to inflorescence or just proximal 1/3, alternate distally, petiole 3–12 mm, ± winged;

blade broadly spatulate to ovate proximally, narrowly ovate to narrowly lanceolate distally, 2–5.5 × 0.8–2.4 cm, base attenuate to cuneate, margins subentire proximally to denticulate distally with 7–16 teeth per side, more marked distally, lateral veins inconspicuous, 4–8 per side, apex obtuse proximally to subacute distally, surfaces glabrous except for strigillose margins;

bracts reduced and narrower.

alternate distally, not fasciculate, petiole 0–2 mm, blade subspatulate proximally to lanceolate, oblanceolate, or narrowly elliptical distally, not folded along midrib, 0.9–2.5 × 0.2–0.6 cm, shorter than internodes, base tapered, margins entire or scarcely denticulate, 1–4 teeth per side, lateral veins obscure, apex subacute or often blunt proximally, surfaces subglabrous or with scattered hairs along margins;

bracts much reduced, sometimes attached to pedicel.

Inflorescences

nodding in bud, later erect, ± open racemes, mixed strigillose and glandular puberulent.

erect racemes or open panicles, relatively loose and uncrowded, branches thin, mixed strigillose and glandular puberulent.

Flowers

suberect;

buds 2–5 × 1.5–3.5 mm;

pedicel 5–15 mm;

floral tube 1–2.2 × 1–3 mm, inner surface glabrous without ring;

sepals often flushed purplish red, frequently keeled, (2–)3–5.5 × 0.9–1.8 mm, abaxial surface sparsely glandular puberulent, sometimes mixed strigillose;

petals white, rarely with red veins or flushed light pink, 3–8.5 × 1.6–4.5 mm, apical notch 0.7–1.4 mm;

filaments white to cream, those of longer stamens 1.4–4 mm, those of shorter ones 1.1–3 mm;

anthers light yellow, 0.4–0.9 × 0.3–0.6 mm;

ovary 20–40 mm, glandular puberulent;

style cream or white, 1.4–4.6 mm, stigma clavate or rarely subcapitate and indented apically, entire, 1.2–2.5 × 0.4–1.6 mm, surrounded by anthers.

erect or, sometimes, nodding in bud;

buds broadly ovoid, 1.2–2.5 × 1–1.5 mm;

floral tube 1.1–1.5 × 1–1.4 mm, usually with ring of spreading hairs at mouth inside;

sepals 0.5–2.5 × 0.4–1.3 mm, apex acute, abaxial surface strigillose, sometimes mixed glandular puberulent;

petals white to pink, 2–5 × 1.5–3 mm, apical notch 0.2–1.9 mm;

filaments white, those of longer stamens 0.5–3 mm, those of shorter ones 0.3–2 mm;

anthers 0.6–1 × 0.5–0.8 mm;

ovary 4–9 mm, mixed strigillose and glandular puberulent;

style light pink, 1–3.5 mm, stigma subclavate to obscurely 4-lobed, 0.4–0.6 × 0.4–0.5 mm, surrounded by longer anthers.

Capsules

slender, sometimes flushed reddish green, ± ascending, 50–100 mm, surfaces sparsely glandular puberulent;

pedicel 15–45 mm.

9–28 mm, surfaces strigillose and glandular puberulent;

pedicel 3–10 mm.

Seeds

narrowly obovoid, 1.1–1.7 × 0.4–0.6 mm, chalazal collar 0.05–0.1 mm, blond or light brown, surface reticulate or sometimes barely rugose;

coma easily detached, white, 7–14 mm.

obovoid, without constriction, 0.9–1.2 × 0.4–0.6 mm, low chalazal collar 0.1–0.2 mm wide, brown, surface reticulate;

coma easily detached, white, 2.5–3 mm.

2n

= 36.

= 26.

Epilobium lactiflorum

Epilobium minutum

Phenology Flowering Jun–Sep. Flowering Apr–Sep.
Habitat Montane stream banks, moist crevices and ledges, gravelly roadsides, burned-over woodlands, sandy moraines, subalpine forests, alpine meadows. Open, dry places, along roads, disturbed areas.
Elevation 50–3800 m. (200–12500 ft.) 90–1900 m. (300–6200 ft.)
Distribution
from FNA
AK; AZ; CA; CO; ID; ME; MT; NH; NM; NV; OR; UT; VT; WA; WY; AB; BC; NB; NL; NS; NT; ON; QC; YT; Greenland; Eurasia
[WildflowerSearch map]
[BONAP county map]
from FNA
CA; ID; MT; NV; OR; WA; BC
[WildflowerSearch map]
[BONAP county map]
Discussion

Epilobium lactiflorum has a nearly circum-subarctic distribution in North America (including coastal Greenland) and Eurasia, extending south into alpine and cool montane habitats along mountain axes. This distribution is similar to that of E. anagallidifolium and E. hornemannii (all with CC chromosomal arrangement), and these species commonly grow in similar habitats as well.

Petal color can be variable in many Epilobium species, but E. lactiflorum (white flowers) differs quite consistently from E. hornemannii (rose-purple to light pink or rarely white) in that feature. Mature fruits and pedicels are also fairly longer in E. lactiflorum. Despite their morphological similarities and broadly overlapping ranges and habitats, E. lactiflorum and E. hornemannii subsp. hornemannii do not appear to hybridize with much frequency, although intermediates, with only moderately reduced seed fertility, might be difficult to detect.

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

Epilobium minutum, like the similar E. foliosum, also occasionally produces cleistogamous flowers, and is modally autogamous in any event. S. R. Seavey et al. (1977b) observed that E. minutum is less common than E. foliosum in the southern part of their overlapping ranges and more common in the north. Several sheets (for example, Lawler 3276, California, Butte Co. [MO]; Nelson & Gordon 5573, California, Trinity Co. [MO]) mention that the plants were growing on serpentine soil. The earliest collection of this species appears to be one made by Archibald Menzies in 1792–1794 under the name E. palustre (BM).

Crossostigma lindleyi Spach (a substitute name for Epilobium minutum) and E. lindleyi (Spach) Rydberg are illegitimate names that pertain here.

(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. Crossostigma
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. 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. 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
Synonyms E. alpinum var. lactiflorum, E. canadense, E. canadense var. albescens, E. hornemannii var. lactiflorum E. minutum var. canescens
Name authority Haussknecht: Oesterr. Bot. Z. 29: 89. (1879) Lindley in W. J. Hooker: Fl. Bor.-Amer. 1: 207. (1832)
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