Plants 22–55 cm, glabrous. Leaf blades linear, 0.2–0.3 × 5–21.5 cm, margins entire. Flowers: tepals yellow adaxially and greenish abaxially, becoming green to coppery, golden brown abaxially and purple-margined adaxially after anthesis,10–12-veined; outer tepal (10–)12–15 × (2.5–)3–3.5 mm; inner tepal (8–)9–12 × (2–)2.5–3.5 mm; stamens 8–9 mm; anthers 2.5–3.5 mm; styles 0.5–1 mm. Capsules 8–10 mm. Seeds 2–3 mm.

Flowering late spring. Open ti-ti and pineland swamps to wet roadside ditches; of conservation concern; 0--10 m; Fla.

Highly localized, Harperocallis flava occurs on gentle slopes, seepage savannas between pinelands, and cypress swamps to precariously open roadside depressions (R. K. Godfrey [1979]; R. Kral 1983; S. W. Leonard and W. W. Baker 1983; D. A. Wood 1996). It has distinctive showy, yellow, solitary flowers, and tuberculate ovaries and fruits. Genetic uniformity among individuals and populations of this species, in which 22 loci were found to be monomorphic, suggests low variability and serious conservation concern (M. J. W. Godt et al. 1997).