Ambrosia L. >

Burrs without hooked appendages, each burr containing 1 fruit (Fig. 41) Ambrosia
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Fruiting head without spines but with teeth, hairy. Perennials
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Leaves pinnatifid, lanceolate to ovate, 10 cm long, c. 3 cm wide. Male involucre 3 mm diam. Perennial herb up to 2 m high with creeping rootstock. Widespread. Weed of roadsides and waste places. Introd. from America. Fl. spring–summer Ambrosia psilostachya