Slender to coarse, smooth perennial 20-100 cm high; stems short, sometimes rhizomatous. Leaves erect or in a fan, (5-)10-30(-40) cm, soft, often with maroon pigment, sheath ciliate or entire, narrowing to blade, apically with short-triangular ligule, blade flattened, 1-5(-7) mm wide, margins lustrous, thickened, smooth, less often papillose or scabridulous. Scapes distally terete, 1-2 mm thick, with several strong ribs; spikes ovoid to lance-cylindric or ellipsoid, 1-2 cm, many-flowered, empty bracts several, grading larger into flowering bracts, these broadly ovate to obovate, 5-7 mm, subentire, narrowly rounded, convex, with distinct dorsal area bisected by a distinct, evidently branched midvein. Lateral sepals free, subequilateral, linear-oblanceolate, 4.5-5 mm, keel lacero-ciliate from middle to apex; petals obovate, 4-5 mm; staminodes bearded; anthers ca. 1.5 mm. Capsule 3-5 mm, placentation parietal; seeds cylindric or fusiform, 1-1.5 mm, amber.
Andes present, French Guiana present, Planalto of Brazil present, Southern America: Colombia (Colombia present), Trinidad present
Colombia E to French Guiana and Trinidad, S east of the Andes into the Planalto of Brazil
This morphologically and ecologically expressive species should include the extreme
X. erythema Maguire & L.B. Smith, as the rhizomal character, the deep red pigmentation and rugulosity of foliage, and the strong ciliation of leaf sheath margins all vary independently through populations in northern South America. The most constant characters remain those of the multicostate, terete scape, venose dorsal area, and the long and distinctively sculpted seed. X. fallax, together with X. jupicai and X. laxifolia comprise the weediest of South American xyrids, quickly coming into wetlands in mechanically disturbed savanna.