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Onagraceae
See list of 7 genera in this family-
1a. Perianth 2-merous [Fig. 738]; fruit indehiscent, covered with uncinate bristles; leaves opposite; petals white
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1b. Perianth 4- to 6-merous; fruit dehiscent (indehiscent in some Oenothera), without uncinate bristles; leaves opposite or alternate; petals absent, or white to pink to purple, or yellow
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2a. Sepals persistent in fruit; androecium with 4 stamens; hypanthium not prolonged beyond the summit of the ovary
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2b. Sepals deciduous in fruit; androecium with 8 stamens; hypanthium prolonged beyond the summit of the ovary (except in Chamerion)
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3a. Flowers zygomorphic, the petals all oriented toward one side of the flower [Fig. 744]; fruit indehiscent, with 2–6 seeds 1.5–3.5 mm long (in part)
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3b. Flowers actinomorphic [Fig. 745]; fruit dehiscent, with many seeds 0.3–2 mm long
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4a. Seeds comose; leaves opposite (especially the lower ones) or alternate throughout in Chamerion; hypanthium not, or only shortly, extending beyond the ovary; petals white to pink to pink-purple
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5a. Hypanthium shortly extending beyond the summit of the ovary; petals 2–16 mm long, notched at the apex; stamens in 2 series, erect to ascending; stigma unlobed or with 4 lobes; new shoots produced from turions, rosettes, or sobols
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5b. Hypanthium not extending beyond the summit of the ovary; petals 10–20 mm long, ± entire at the apex; stamens in 1 series, declined; stigma with 4 conspicuous lobes; new shoots produced from lateral roots (or sometimes by sobols)
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4b. Seeds not comose; leaves alternate; hypanthium extending beyond the summit of the ovary; petals yellow (sometimes fading to red) or pink to light purple or red-purple (rarely white) in Clarkia
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6a. Petals pink to light purple or red-purple (rarely white), with a pair of small lobes or recurved teeth on the claw; anthers basifixed
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6b. Petals yellow (sometimes fading to red), lacking lobes or teeth on the claw; anthers mesifixed (i.e., versatile)
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7a. Petals with 1 or 2 red dots near the base; stigma capitate or hemispherical
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7b. Petals without basal red dots; stigma with 4 lobes (caution: the lobes short in O. serrulata) (in part)
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Each photo represents one genus in this family.