Guinea-fowl grass

Rottboellia cochinchinensis, the itch grass or guinea-fowl grass, is a robust annual grass of the Poaceae, native to tropical Africa and Asia and now a serious weed of row crops across the tropics. Plants are tufted but can become rhizomatous, reaching 1–3 m tall with stout, hollow culms 1–2 cm in diameter and conspicuous prop roots from lower nodes. Leaf sheaths are densely covered with stiff, irritating, silica-tipped trichomes that cause skin itching on contact; ligules are short and membranous. Blades are flat, 30–60 cm long, 10–25 mm wide, with a prominent white midrib. The inflorescence is a cylindrical, jointed raceme 5–15 cm long, 4–7 mm wide, breaking apart at maturity into barrel-shaped joints each containing a sessile bisexual spikelet sunk into the rachis plus a pedicellate staminate spikelet. The lower glume is thick, polished, and bony. Flowering occurs through the warm season, and seed dormancy is enforced by the indurated rachis joint.