Herbs, perennial, 6-15 dm. Stems ascending to spreading, often clambering, pubescent, glabrate. Leaves sessile; blade ovate to lanceolate or elliptic, 1.8-8 × 0.5-3 cm, herbaceous, apex long-acuminate or acute, sparsely strigose or glabrous. Inflorescences terminal and axillary, pedunculate; heads yellowish white, subglobose to cylindric, 0.9-2.5(-4) × 0.9-1 cm; bracts keeled, less than 1/2 as long as tepals. Flowers: tepals monomorphic, green, lanceolate, 3.4-4.7 mm, apex acute, villous, hairs not barbed; stamens 5; pseudostaminodes ligulate, margins laciniate. Utricles included within tepals, greenish yellow, ellipsoid, 2.5 mm, apex acute. Seeds ovoid, 1.2-1.3 mm. Flowering year-round. Coastal hammocks, thickets, sand bars; 0 m; introduced; Fla.; Mexico; West Indies; South America. Alternanthera flavescens has long been known as A. ramosissima (Martius) Standley.