Gentes Herbarum 11: 357. 1978.
Plants often multistemmed, from fibrous-thickened root crown, 1–2 m, herbage variously hispid or scabrid, hairs stellate or simple. Stems sparingly to freely branched. Leaves: stipules linear-subulate, 2.5–6 mm; petiole of lower leaves 1/4–2/3 times blade; blade narrowly ovate to transversely ovate, sometimes palmately, hastately, or sagittately 3(–5)-lobed, 3–8 × 1.5–6.5 cm, margins irregularly serrate to crenate, apex broadly acute to acuminate. Inflorescences solitary flowers in axils of distal leaves or leafy, open panicles. Pedicels exceeding petioles, sometimes blades; involucellar bractlets 6–7, linear to subulate, 2–3 mm. Flowers: calyx divided for 2/3–4/5+ its length, campanulate to rotate, 3.2–6 mm; corolla rotate, petals usually white, usually with yellow base, sometimes with pink blush, sometimes drying yellowish, asymmetrically ovate to orbiculate, 5–14 × 5–10 mm; staminal column straight or declinate, yellow, 4–10 mm, bearing filaments mostly in distal 1/2–2/3; filaments 1.5 mm; anthers subsessile, yellow; pollen yellow; styles white or pink, 1.5–2 mm; stigmas pink. Capsules olivaceous to brown, 8–11 mm diam., valve margins angulate or subangulate in outline, variously short-hairy, with prominent curved or hooked, simple hairs on sutures. Seeds brown, 2.5–2.8 mm, minutely hairy. 2n = 38 (Mexico, as K. pentasperma).
Phenology: Flowering fall.
Habitat: Freshwater and brackish marshes near coast
Elevation: 0–10 m
Fla., Tex., Mexico, West Indies, Central America, South America (Colombia, Ecuador, Peru, Venezuela).
Kosteletzkya depressa is variable and barely enters the flora area. The southern Texas plants conform more to Mexican populations in characters of leaves, fruits, and seeds; in the same characters, the southern Florida plants show affinity with populations of the Greater Antilles.
An earlier chromosome count of 2n = 34 for Kosteletzkya depressa (A. Skovsted 1941) has been shown to be incorrect (O. J. Blanchard 1974).
Plants of Kosteletzkya depressa are said to have stinging or irritating hairs.