Alternanthera philoxeroides (Mart.) Griseb.

Perennial herb; stems creeping or floating, ascending towards apex, rooting at the lower nodes, branched, hollow, with a longitudinal hairy groove on 2 opposite sides. Lvs subsessile or with petiole to 5 mm long, with a ring of white hairs between the 2 opposite lf bases. Lamina 3–13 × 1–3.5 cm, elliptic to oblanceolate or obovate, glabrous or slightly hairy near the attenuate base; apex obtuse or acute. Infls in upper axils, mostly 1–2 cm diam., capitate, white; peduncles to 9 cm long with 2 opposite longitudinal hairy grooves, occasionally heads shortly pedunculate and terminal. Bracts 2.5–3.5 mm long, ovate-acuminate; bracteoles similar to bracts, somewhat smaller, persistent. Tepals 5–7 mm long, oblong to ovate, acute or obtuse. Fertile stamens 5; staminodes = stamens. Style short, thick; stigma capitate. Fr. not seen.

[From: Webb et al. (1988) Flora of New Zealand. Volume 4.]