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FOC | Family List | FOC Vol. 13 | Onagraceae

5. Oenothera Linnaeus, Sp. Pl. 1: 346. 1753.

月见草属 yue jian cao shu

Authors: Jiarui Chen, Peter C. Hoch & Warren L. Wagner

Oenothera rosea

Credit: Harvard University Herbaria

Annual, biennial or perennial herbs, caulescent or acaulescent, with a taproot or fibrous roots, occasionally with rhizomes or shoots arising from spreading lateral roots. Leaves alternate or in a basal rosette that often is absent in mature plants, entire, toothed to pinnatifid; stipules absent. Flowers perfect, actinomorphic, in axils of upper leaves, when numerous forming terminal leafy spikes, racemes, or corymbs, opening near sunset or near sunrise. Floral tube usually well developed, cylindric and somewhat flared near mouth, deciduous soon after anthesis. Sepals 4, green or yellowish, often tinged or striped red or purple. Petals 4, yellow, purple, pink, or white. Stamens 8; anthers versatile; pollen shed singly. Ovary with 4 locules; ovules numerous; stigma divided into 4 linear lobes, receptive all around, and subtended by a ± conspicuous ringlike indusium in early development, but often obscured when receptive. Fruit a dehiscent capsule [rarely indehiscent outside of China], straight or curved, terete to 4-angled or winged, sessile, occasionally pedicellate, or basal portion sterile and stipelike. Seeds numerous, in 1 or 2(or 3) rows or in clusters in each of 4 locules. 2n = 14, 28, 42, 56.

One hundred and twenty-one species: open, often disturbed habitats in temperate to subtropical areas of North, Central, and South America, with the center of diversity in SW North America; ten species (all naturalized within the past 200 years) in China.

Oenothera is currently divided into 15 sections, only three of which are represented in China. An evolutionary phenomenon that has occurred repeatedly in Oenothera (52 species) and several other genera of tribe Onagreae is permanent translocation heterozygosity, a peculiar, specialized genetic system based on heterozygosity for successive chromosomal translocations and manifested by autogamy and formation of a ring of 14 chromosomes at meiotic metaphase I (for reviews see Cleland, Oenothera Cytogenetics and Evolution. 1972; Holsinger and Ellstrand, Amer. Naturalist 124: 48-71. 1984). Permanent translocation heterozygote individuals breed true for their series of reciprocal translocations and are maintained by either balanced lethals or selective fertilization. These plants are essentially clonal. Many species of Oenothera that have become naturalized outside their natural range are permanent translocation heterozygotes, as noted in their descriptions.

Several ornamental species of Oenothera are known only from cultivation in China, often in Beijing, Kunming, or other botanical gardens. For example, O. macrocarpa Nuttall subsp. macrocarpa (O. sect. Megapterium (Spach) Endlicher) is native to the Great Plains region of C North America but has never become naturalized outside of its indigenous distribution because it is a self-incompatible outcrosser with rather specific habitat requirements. It can be distinguished by its large, yellow corollas (up to 14 cm in diam. at anthesis), 4-winged capsules (wings up to 3.4 cm wide), floral tube (7.8-)9.5-11.5(-14) cm, and coarsely rugose, distally winged seeds. A second species, O. acaulis Cavanilles (O. sect. Lavauxia (Spach) Endlicher, O. subsect. Australis W. L. Wagner & Dietrich), likewise known only from cultivation in China, is native to S South America and is characterized by white petals and capsules winged in the distal half.

1 Petals white, pink, or purple; capsules clavate or obovoid, valves sharply angled, winged or ridged, proximally narrowed into a tapering, sterile stipe; seeds in indistinct rows or clusters in each locule   (2)
+ Petals yellow, at least before fading; capsules lanceoloid or cylindric, sometimes slightly enlarged toward apex, valves acute or obtuse to rounded, not narrowed toward base into a sterile stipe; seeds in two rows in each locule   (3)
2 (1) Petals 16-38 mm, white, fading to rose-purple; sepals 16-32 mm; leaf margin weakly serrate to sinuate-pinnatifid, often with large terminal lobe; pollen ca. 90+% fertile.   9 O. tetraptera
+ Petals 5-12 mm, pink to rose purple; sepals 5-10 mm; leaf margin subentire to coarsely dentate, sometimes sinuate-pinnatifid at leaf base; pollen ca. 50% fertile.   10 O. rosea
3 (1) Capsules cylindric and ± slightly enlarged toward apex; erect to procumbent annual or short-lived perennial herbs, 5-80(-100) cm tall, rarely biennial; flowers few in upper axils; seeds ellipsoid, brown to dark brown   (4)
+ Capsules lanceoloid; coarse erect biennial herbs (10-)30-200 cm tall; flowers numerous in generally dense spikes; seeds irregularly angled, dark brown to black   (6)
4 (3) Floral tube 25-50 mm; sepals 13-33 mm; petals 20-45 mm; stigma exserted beyond anthers at anthesis; pollen ca. 90+% fertile; flowers primarily outcrossing.   7 O. drummondii
+ Floral tube 12-35 mm; sepals 5-25 mm; petals 5-25(-35) mm; stigma surrounded by anthers at anthesis; pollen ca. 50% fertile; flowers primarily self-pollinating   (5)
5 (4) Leaf margin deeply lobed to dentate; sepals 5-15 mm; petals 5-22 mm, yellow to pale yellow; capsule cylindric throughout.   6 O. laciniata
+ Leaf margin serrate and usually somewhat undulate; sepals 12-25 mm; petals 15-25(-35) mm, yellow, often with basal red spot; capsule cylindric, enlarged toward apex.   8 O. stricta
6 (3) Floral tube 35-50 mm; stigma elevated above anthers at anthesis, flowers mostly outcrossed; petals 35-50 mm; leaf surface often crinkled.   3 O. glazioviana
+ Floral tube 15-40 mm; stigma surrounded by anthers at anthesis, flowers mostly self-pollinating; petals 7-25(-30) mm; leaf surface smooth   (7)
7 (6) Free sepal tips 0.5-3 mm, apical; dry capsules grayish green or dull green; apex of inflorescence erect   (8)
+ Free sepal tips 0.5-5 mm, distinctly subapical; dry capsules rusty brown to black; apex of inflorescence usually curved or sigmoid   (9)
8 (7) Leaves grayish green, with prominent pale green veins; sepals 9-18 mm; stems ± exclusively densely strigillose; inflorescence dense, apex truncate from widely spreading bracts.   1 O. villosa
+ Leaves pale green, with inconspicuous veins; sepals 12-22(-28) mm; stems densely or sparsely strigillose and villous; inflorescence relatively open, apex obtuse from erect to slightly spreading bracts.   2 O. biennis
9 (7) Stems 10-60 cm tall, erect or procumbent, lower portions conspicuously pubescent; leaves grayish green, with inconspicuous veins; capsules dark to dull green, sometimes reddish, drying rusty brown.   4 O. oakesiana
+ Stems 30-150 mm tall, erect, lower portions inconspicuously pubescent; leaves bright green, with white or red veins; capsules dark green, often drying black.   5 O. parviflora

Lower Taxa


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