Biennials; blackening upon drying. Stems simple or branched distally, 2–8 dm, appressed-hirsute or spreading-hirsute proximally, appressed-hirsute or glabrous distally. Leaves much smaller distally; larger blade: major vein 1, minor veins (0–)2, narrowly oblanceolate, lanceolate, or broadly linear, 25–60 x 3–12 mm, margins entire or crenate, teeth 0.5–1.5 mm, apex obtuse or rounded, sometimes acute, surfaces glabrate or appressed-pilose. Spikes: bracts ovate-lanceolate, 1.5–4 mm. Pedicels 0.5–1 mm; bracteoles 1–2 mm. Flowers: calyx 4.5–5.5 mm, tube obscurely 10-nerved, ascending- to appressed-hispid, hairs often pustular-based; corolla 10–16 mm, glabrate externally, lobes 2–5 mm; style included, 1–2 mm. Capsules blackish, ovoid, 4.5–6.5 mm, glabrate. Seeds 0.5–0.7 mm.
Phenology: Flowering May–Oct.
Habitat: Moist pine savannas, flatwoods, streamhead ecotones, seepage slopes, pitcher-plant bogs.
Elevation: 0–150 m.
Ala., Ark., Fla., Ga., La., Miss., N.C., S.C., Tex., Mexico (Yucatán), West Indies (Bahamas, Cuba, Dominican Republic, Jamaica), Central America (Belize).
Buchnera floridana is mostly restricted to the Coastal Plain, occurring primarily in fire-maintained, pine-graminoid ecosystems in strongly acidic soils. Collections also have been made from higher pH soils of chalk prairies in Alabama and Mississippi and from limestone substrates in Florida and Texas; in the Caribbean, it regularly occurs in limestone soils. The situation in Texas is unusual in that B. floridana occurs far inland as well as on the Coastal Plain; most Texas specimens of Buchnera belong to B. floridana; B. americana is known from counties along the Red River and in the pinelands of eastern Texas.
Some specimens of Buchnera floridana from southern Florida and the Keys have slender leaves and reduced indument on the calyx, which are typical of B. longifolia Kunth (= B. elongata Swartz; both names have been applied to Florida plants) of the Caribbean, Central America, and South America; they lack the glabrous corollas, long calyces, and large inflorescence bracts of B. longifolia. The presence of one or more B. longifolia characteristics in southern Florida plants may be the result of past contact between the two species; there is no evidence that the two come into contact in Florida at present.