Herbs, perennial, cespitose or solitary, 30--100 cm. Leaves in broad or narrow fans, (5--)10--40(--50) cm; sheath base tan, straw-colored, or pale pink; blade pale or olive green, linear-triangular, (2--)3--7(--10) mm wide, smooth or slightly papillate, margins smooth to minutely scabrous or papillate. Inflorescences: scape sheaths much exceeded by leaves; scapes linear, rarely flexuous, terete or nearly terete, 1--1.5 mm wide, distally usually 2-ribbed, sometimes with additional ribs; spikes ovoid to ellipsoid, lanceoloid, or cylindric, 10--20(--30) mm; fertile bracts 5--8 mm, margins entire, apex rounded. Flowers: lateral sepals included, dark brown, strongly curved, 4--7 mm, keel firm, ciliate, petals unfolding in morning, blade obovate, 10 mm; staminodes bearded. Seeds translucent, ovoid to ellipsoid, 0.5--0.6 mm, finely multiribbed and cross ribbed. 2n = 18. Flowering late spring--fall (all year south). Acid, sandy, moist pine or oak savanna, pine flatwoods, pond shores, ditches, bogs; 0--300 m; Ala., Ark., Fla., Ga., La., Miss., N.C., S.C., Tenn., Tex., Va.; Mexico; West Indies (Cuba); Mexico; Central America (Belize, Honduras, Nicaragua). Xyris ambigua is one of the more widespread and weedy of xyrids, frequently invading disturbed moist, sandy areas. It is also one of the most variable in habit and apparently forms intermediates with X. stricta and X. torta.
Lvs broadly linear, spreading, scarcely twisted, mostly 10-40 cm נ3-20 mm, lustrous dark green, the firm, thickened base brownish or stramineous, only rarely anthocyanic, the plant tending to be invested with the stubble of old fibrous lf-bases; inner surface of inner lvs with prominent dark longitudinal veins; scapes (2-)5-10 dm, twisted, many-ribbed below, becoming flattened and 2-edged above; spikes 1-3 cm at maturity, many-fld, lance-ovoid or ellipsoid; lateral sep shortly included, curved, the broad, thickened keel ciliate-scabrid; pet-blades yellow, obovate, 8 mm, unfolding in the morning; seeds plump, 0.5-0.6 mm, finely ridged; 2n=18. Moist or wet low ground, often in grass-sedge bogs or savannas or along the upper edges of wet places; coastal plain from Va. to Fla. and Tex. Early summer-fall.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.