Ambrosia L.
Burrs without hooked appendages, each burr containing 1 fruit (Fig. 41) Ambrosia
Fruiting head without spines but with teeth, hairy. Perennials
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
Leaves 2–4-pinnate, linear to oblong, mostly up to 10 cm long. Perennial herb with long suckering roots. Widespread. Weed of roadsides and waste places. Introd. from America. Fl. spring–summer Ambrosia tenuifolia