Epilobium rigidum
Epilobium sect. Macrocarpa
rigid willowherb, Siskiyou Mountains. willowherb, stiff willowherb
several to many, suberect or ascending, terete, 10–40 cm, simple or sparsely branched, usually glabrous and ± glaucous proximal to inflorescence, strigillose distally, sometimes densely strigillose throughout.
± woody at base, epidermis peeling proximally.
crowded distally, petiole 2–6 mm, blade narrowly ovate to ovate or broadly elliptic, often obovate in proximal pairs;
cauline 2–4.5 × 0.8–2 cm, base rounded to attenuate, margins subentire or finely denticulate, 8–12 teeth per side, lateral veins inconspicuous, 3–5 per side, apex obtuse proximally to subacute distally, surfaces glaucous and subglabrous to densely strigillose;
bracts narrower and much smaller.
opposite proximal to inflorescence, alternate distally.
erect racemes, simple, ± densely strigillose, rarely mixed sparsely glandular puberulent.
erect;
buds 6–11 × 4–5 mm, apiculate;
pedicels 4–8 mm;
floral tube 1–1.8 × 2–3 mm, with raised ring of tissue edged with spreading hairs at mouth inside;
sepals often reddish green, lanceolate, 9.5–14.5 × 2.5–3.5 mm, apex acuminate, abaxial surface densely strigillose;
petals pink to rose-purple, obcordate, 16–20 × 13–16 mm, apical notch 3.4–5.5 mm;
filaments light pink, those of longer stamens 9–14 mm, those of shorter ones 6.5–10 mm;
anthers cream, 1.8–3.5 × 1–1.9 mm;
ovary 6–12 mm, densely strigillose;
style cream to light pink, 14.5–18.5 mm, stigma broadly 4-lobed, 1–1.5 × 3–3.5 mm, exserted beyond anthers.
actinomorphic;
floral tube extremely short for size of flower, without bulbous base and scales inside;
petals pink to rose-purple;
pollen shed in tetrads;
stigma deeply 4-lobed.
20–35 mm, surfaces strigillose;
pedicel 9–13 mm, bracts often attached 2–3 mm from base.
narrowly fusiform to cylindrical, splitting to base, central column persistent, pedicellate.
narrowly obovoid, constriction 0.6–0.8 mm from micropylar end, 2.5–3.4 × 0.9–1.4 mm, chalazal collar obscure, light brown, surface papillose;
coma easily detached, white, 6–8 mm.
numerous, in 1 row per locule, narrowly obovoid, prominently constricted near micropylar end, coma present.
= 36.
Epilobium rigidum
Epilobium sect. Macrocarpa
Within its range in northwestern California and southwestern Oregon, Epilobium rigidum is restricted to unusually dry habitats compared to most species in sect. Epilobium, but is not unlike taxa in the non-n = 18 clade, which are both perennial and annual. It is self-compatible, but with strongly protandrous flowers and an exserted stigma, and is modally outcrossing, pollinated by bees and flies.
Plant vestiture varies from subglabrous to densely strigillose throughout (var. canescens), but plants with these differences can be in the same population, and no other morphological differences between them have been found.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Species 1.
Section Macrocarpa consists of only Epilobium rigidum, an uncommon species endemic to the Klamath-Siskiyou region along the California-Oregon border in western United States. Since its publication in the worldwide monograph of Epilobium by C. Haussknecht (1884; see also P. C. Hoch and P. H. Raven 1990), this species has been included consistently in sect. Epilobium in the strict sense (Raven 1976), despite having a number of unusual morphological features. It has the largest seeds in the genus (2.5–3.4 × 0.9–1.4 mm), with a prominent constriction near the micropylar end (S. R. Seavey et al. 1977), in both features resembling seeds of sects. Cordylophorum, Crossostigma (only E. foliosum), Xerolobium, and Zauschneria but unlike any taxa in sect. Epilobium. Despite having some of the largest petals in the genus (16–20 mm), E. rigidum has an extremely short floral tube (1–1.8 mm), and this combination of character states is unique. It shares with sect. Epilobium the chromosome number n = 18, and can form hybrids with some species in that section; however, all hybrids are completely sterile, and no bivalents form at meiotic metaphase I (Seavey and Raven 1977b, 1978). Analysis of ITS sequence data (D. A. Baum et al. 1994) placed E. rigidum as the sister branch to sect. Epilobium but with essentially no support, even considering the sparse sampling of the section (five species). R. A. Levin et al. (2004), using both ITS and trnL-F sequence data, found very strong support for both a sparsely sampled sect. Epilobium and for a clade of all sections with chromosome numbers other than n = 18; E. rigidum is weakly supported as the basally diverging branch on the non-sect. Epilobium clade. The current best molecular evidence places E. rigidum near the base of the genus, possibly on a branch with all other species having n = 18 (sect. Epilobium), or more likely (with weak support) on the branch with all non-n = 18 species, with which it shares similarities in seed and pollen morphology. This apparent basal position and the unique short floral tube (which might even be seen as transitional to the character state in the tubeless sister genus, Chamaenerion) suggest that E. rigidum is best treated as a separate section, positioned near the base of the two well-supported clades in Epilobium.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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