FNA: Chamaenerion vs. Onagraceae

Distribution

North America; Mexico; Eurasia; nw Africa; Atlantic Islands (Iceland)

North America; Mexico; Central America; South America; West Indies; Bermuda; Eurasia; Africa; Atlantic Islands; Indian Ocean Islands; Pacific Islands; Australasia; nearly worldwide; primarily New World

[BONAP county map]

Discussion

Species 8 (2 in the flora).

J. Holub (1972b) argued that the correct name for this group, when segregated from Epilobium, should be Chamerion (Rafinesque) Rafinesque ex Holub. However, A. N. Sennikov (2011), using the more recent and clarified ICBN (Melbourne Code), correctly argued that the name of the segregated genus should be Chamaenerion, and that opinion is followed here.

All species of Chamaenerion tested to date have been self-compatible, although the strong protandry can result in low fertilization rates if there is a shortage of pollinators. Flowering is diurnal, with each flower generally remaining open for three to five or more days.

All eight species (nine taxa) of Chamaenerion are restricted to the northern hemisphere, and six of eight species occur only in Eurasia; Circaea is the only other genus of Onagraceae in which most species occur outside of the western hemisphere (D. E. Boufford 1982b). Chamaenerion is generally divided into two sections, each with four species (T. Tacik 1959; and, as Chamerion, J. Holub 1972b; W. L. Wagner et al. 2007). P. H. Raven (1976) and most others who treated this group as a section of Epilobium divided it into two corresponding subsections. Both species of Chamaenerion in North America are placed in sect. Chamaenerion (not treated formerly here), along with two species endemic to the Himalayan region, C. conspersum (Haussknecht) Kitamura and C. speciosum (Decaisne) Hoch & Gandhi (Chen C. J. et al. 1992); the other four species, all endemic in Eurasia, comprise sect. Rosmarinifolium Tacik.

Chamaenerion differs from Epilobium in leaves nearly always alternate, rarely subopposite or verticillate near stem base (versus opposite at least on proximal stem); absence of a floral tube (versus a distinct floral tube); slightly zygomorphic flowers with subequal stamens that are erect, later deflexed, and a style that is deflexed, later erect (versus actinomorphic flowers with erect stamens in two unequal series and erect style); and pollen shed in monads (versus pollen shed in tetrads, or monads in one species). Molecular analyses (D. A. Baum et al. 1994; R. A. Levin et al. 2004) provided strong support for Chamaenerion as a monophyletic group separate from Epilobium, and for sect. Chamaenerion (only C. angustifolium and C. latifolium sampled) as monophyletic.

The superfluous and illegitimate name Pyrogennema Lunell pertains here.

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

Genera 22, species 664 (17 genera, 277 species in the flora).

Members of the Onagraceae are especially richly represented in North America. The family comprises annual and perennial herbs, with some shrubs and a few small to medium-sized trees. Most species occur in open habitats, ranging from dry to wet, with a few species of Ludwigia aquatic, from the tropics to the deserts of western North America, temperate forests, and arctic tundra; some species of Epilobium, Ludwigia, and Oenothera can be weeds in disturbed habitats. Members of the family are characterized by 4-merous flowers (sometimes 2-, 5-, or 7-merous), an inferior ovary, a floral tube in most species, stamens usually two times as many as sepals, and pollen connected by viscin threads. Flowers are usually bisexual, sometimes unisexual, and plants are gynodioecious, matinal, diurnal, or vespertine, self-compatible or self-incompatible, often outcrossing and then pollinated by a wide variety of insects or birds, or autogamous (P. H. Raven 1979; W. L. Wagner et al. 2007).

Onagraceae are known in considerable systematic detail, and information is available on comparative breeding systems and pollination biology, on chromosome numbers and cytogenetic relations, often involving translocations, and on vegetative, floral, and seed anatomy, palynology, and embryology. The phylogeny of the family is known in reasonably good detail, with most parts of the trees generally well-supported.

The suprageneric and generic classification presented by W. L. Wagner et al. (2007) differs in a number of ways from the previous classification (P. H. Raven 1979, 1988). Onagraceae are divided into two subfamilies based on a fundamental basal split recognized in all phylogenetic studies (R. H. Eyde 1981; P. C. Hoch et al. 1993; R. A. Levin et al. 2003, 2004; V. S. Ford and L. D. Gottlieb 2007), with Ludwigia on one branch (as Ludwigioideae), and the rest of the family on a second branch (as Onagroideae). Onagroideae are subdivided into six tribes: Circaeeae (including Fuchsieae), Epilobieae, Gongylocarpeae, Hauyeae, Lopezieae, and Onagreae. The Epilobieae and Onagreae are diverse; together they constitute fully two-thirds of the species in the family and include 15 of the 22 genera. The classification following Wagner et al. can be viewed on the Onagraceae web site by Wagner and Hoch at http://botany.si.edu/Onagraceae.

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

Key

1. Leaf blades elliptic or ovate to lanceolate-elliptic, 2–5(–8) × 0.6–1.7(–2) cm, without submarginal vein, petioles 0–2 mm; bracts ca. 1/2 as long as cauline leaves; seeds fusiform, 1.2–2.1 × 0.4–0.6 mm, with distinct chalazal collar (0.1–0.2 mm); styles glabrous, shorter than stamens.	C. latifolium
1. Leaf blades lanceolate to linear, proximally oblong to obovate, (3–)5–23 × 0.3–3.4 cm, with ± prominent submarginal vein, petioles 0–7 mm; bracts much smaller than cauline leaves; seeds narrowly obovoid to oblong, 0.9–1.3 × 0.3–0.4 mm, with inconspicuous chalazal collar (to 0.1 mm); styles pubescent proximally, longer than stamens.	C. angustifolium

1. Sepals persistent or tardily caducous after anthesis; flowers (3 or)4 or 5(–7)-merous; floral tube absent; petals yellow or white [a. Onagraceae subfam. Ludwigioideae, p. 70].	Ludwigia
1. Sepals deciduous after anthesis (along with other flower parts); flowers (2–)4-merous; floral tube usually present, often elongate, if absent then petals usually rose purple or pink, rarely white [b. Onagraceae subfam. Onagroideae, p. 101].	→ 2
2. Stipules present and soon deciduous; fruit indehiscent (berry or burlike capsule with hooked hairs) [b1. Onagraceae subfam. Onagroideae tribe Circaeeae, p. 101].	→ 3
3. Fruit a berry; seeds few to ca. 500; flowers 4-merous.	Fuchsia
3. Fruit a capsule, burlike, with stiff, hooked hairs; seeds 1 or 2; flowers 2-merous.	Circaea
2. Stipules absent; fruit usually a capsule, sometimes indehiscent.	→ 4
4. Seeds usually comose, coma rarely secondarily lost; sepals erect or spreading; stigmas with dry multicellular papillae, entire or 4-lobed, lobes commissural; x = 18 [b2. Onagraceae subfam. Onagroideae tribe Epilobieae, p. 107].	→ 5
5. Floral tube absent; stamens subequal; style deflexed at anthesis, later erect, stamens initially erect, later deflexed; leaves usually alternate, rarely subopposite or subverticillate proximally.	Chamaenerion
5. Floral tube present; stamens in 2 unequal whorls; style and stamens erect; leaves opposite, at least near base of stem.	Epilobium
4. Seeds not comose; sepals reflexed; stigmas usually wet, non-papillate, and entire or (3 or)4-lobed (non-commissural), sometimes (Clarkia) lobes commissural and then with dry unicellular papillae; x = 7 [b3. Onagraceae subfam. Onagroideae tribe Onagreae, p. 159].	→ 6
6. Stigmas with commissural lobes and dry, unicellular papillae; flowers usually protandrous.	Clarkia
6. Stigmas hemispherical to subglobose or subcapitate, peltate, or 4-lobed, not commissural, surface wet, non-papillate; flowers not protandrous.	→ 7
7. Ovaries 2-locular; stems usually delicate.	Gayophytum
7. Ovaries (3 or)4-locular; stems usually not especially delicate.	→ 8
8. Seeds with concave and convex sides, concave side with a thick wing, convex side covered with glasslike, clavate hairs; petals white with yellow basal area.	Chylismiella
8. Seeds not concave/convex and not with a wing and clavate hairs; petals yellow, purple, red, or white, if white, mostly without yellow base.	→ 9
9. Ovaries with a slender, sterile apical projection; plants usually acaulescent.	→ 10
10. Herbs perennial; sterile projection of ovary persistent with fertile part in fruit, projection without visible abscission lines at its junctures with floral tube or fertile part of ovary.	Taraxia
10. Herbs annual; sterile projection of ovary with visible abscission lines at its junctures with both short floral tube and fertile part of ovary.	Tetrapteron
9. Ovaries without an apical projection; plants usually caulescent, sometimes acaulescent (in Oenothera).	→ 11
11. Styles with peltate indusium at base of stigma, at least at younger stages prior to anthesis; stigmas (3 or)4-lobed, receptive all around (or peltate to discoid or nearly square in sect. Calylophus).	Oenothera
11. Styles without indusium; stigmas usually subglobose to globose, subcapitate, capitate, or cylindrical (Eulobus), rarely conical-peltate and ± 4-lobed.	→ 12
12. Seeds in 2 rows per locule; capsules pedicellate; leaves mostly basal, blades often pinnately lobed, rarely bipinnately, sometimes unlobed, or lateral lobes greatly reduced or absent, terminal lobe usually large, abaxial surface of leaves or leaf margins with conspicuous, usually brown, oil cells.	Chylismia
12. Seeds in 1 row per locule; capsules usually sessile, rarely very shortly pedicellate; leaves not predominately basal, blades not lobed or pinnatifid, leaves without oil cells.	→ 13
13. Petals usually white, rarely red or tinged red; flowers vespertine.	Eremothera
13. Petals yellow, often with red flecks or spots; flowers diurnal.	→ 14
14. Flowering stems virgate; leaf blades pinnatifid to lobed; petals yellow with red flecks near base; seeds usually with purple spots; floral tube with a lobed disc.	Eulobus
14. Flowering stems not virgate; leaf blades not pinnatifid, margins entire or toothed; petals yellow, sometimes with 1+ red spots at base; seeds without purple spots; floral tube without a lobed disc.	→ 15
15. Stems densely leafy distally, nearly leafless proximally, with many slender, ascending branches from base; capsules strongly flattened, straight.	Neoholmgrenia
15. Stems usually leafy throughout, branched throughout or with a few basal branches; capsules not flattened, subterete or 4-angled, often flexuous or curled, sometimes straight.	→ 16
16. Capsules subterete; flowers only from distal nodes; seeds appearing smooth, glossy, triangular in cross section.	Camissonia
16. Capsules 4-angled, at least when dry; flowers from basalmost to distal nodes; seeds dull, flattened.	Camissoniopsis