"Three other spp. are merely casual with us. A. leptophyllum (Pers.) F. Muell., of trop. and subtrop. Amer., is an annual with filiform lf-segments. A. repens (Jacq.) Lag. and A. nodiflorum (L.) Lag. are Mediterranean rhizomatous perennials. The former has a well developed involucre, the latter does not."
Fruit ovoid to almost round, laterally compressed, 1.25–2 mm. long, with narrow, prominent, pale primary ribs; stylopodia small, flat; styles slender, ± twice as long as the stylopodia.
Stems finely striate, fleshy and fistular, ± 0.3–1.6 cm. in diameter, simple or branched.
Weak, trailing or ascending perennial, glabrous, rooting at the lower nodes with clusters of white rootlets, 11–80(–100) cm.
Umbels leaf-opposed, sessile or shortly (to ± 4 mm.) pedunculate, with 5–10 unequal rays ± 8–30 mm. long; involucre commonly absent, occasionally of up to 3 narrowly lanceolate bracts up to ± 3 mm. long, especially in pedunculate umbels; flowers ± 12–20 in each partial umbel, pedicels (0–)1.5–5 mm.; involucel conspicuous, of 5–7 lanceolate, nervose, acute, pale-margined bracteoles 3–6 mm. long.
Lower and middle stem leaves with the lamina ovate to oblong in outline, 4–40 cm. long, pinnate with 2–6 pairs of sessile leaflets; leaflets lanceolate to ovate, (5–)9–55(–75) × (3.5–)5–20(–40) mm., regularly or irregularly dentate, the terminal in particular sometimes ± lobed; petiole 1.5–12 cm.; sheaths 15–35(–50) mm., narrowly oblong, striate, membranous-margined; upper leaves sessile, shorter, with fewer leaflets.