Ambrosia tenuifolia

Erect perennial herb to 75 cm high, stoloniferous; stems sparsely branched, with long spreading hairs. Leaves alternate or opposite, rhombic in outline, mostly 2–8 cm long and 4–5 cm wide, bipinnatisect with linear segments mostly less than 1.5 mm wide, surfaces greyish from a covering of long white hairs; petiole to 2 cm long. Inflorescences solitary or few together, 3–7 cm long. Male capitula numerous, 2–4 mm diam., greenish or white; peduncles c. 1 mm long; florets many, slightly exceeding involucral bracts. Female capitula solitary or in small clusters in upper axils; fruiting capitula ovoid, 3–4 mm long, reticulate or slightly ribbed, with 4–6 short spines above, apex with a long central beak. Flowers spring and summer.