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Ludwigia
See list of 4 species in this genusReferences: Munz (1944), Peng et al. (2005).
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1a. Leaves opposite, the blades 5–30 mm long, abruptly narrowed to a broad petiole; flowering stems prostrate or creeping, often rooting at the nodes
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1b. Leaves alternate, the principal blades 40–105 mm long, gradually tapering to the stem or a subpetiolar base; stems upright
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2a. Flowers borne on pedicels (2–) 3–5 mm long, with conspicuous yellow petals 5–7 mm long; roots usually tuberous-thickened
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2b. Flowers sessile or subsessile, lacking petals or sometimes with minute, green petals; roots not thickened
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3a. Fruit 4–7 mm long, longer than wide, glabrous; bracteoles 2–5 mm long, attached at or above the base of the fruit [Fig. 742]; branches wing-angled
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3b. Fruit 2.5–4 mm long, subglobose, pubescent; bracteoles wanting or shorter than 1 mm, when present attached at the base of or below the fruit; branches scarcely, if at all, wing-angled
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Each photo represents one species in this genus.