Stems simple or branched, 50–80 cm; branches ascending, subterete, ridged proximally, quadrangular-ridged distally, glabrous or scabridulous. Leaves spreading-ascending, widely spaced; blade linear to linear-filiform, 10–30 x 0.5–1.4 mm, not fleshy, margins entire, adaxial surface scabrous; axillary fascicles absent or shorter than subtending leaves. Inflorescences racemes, elongate, flowers 2 per node, nodes widely spaced; bracts much longer than pedicels. Pedicels erect-ascending, 0.5–4(–5) mm, glabrous. Flowers: calyx funnelform-obconic, tube 4–6 mm, glabrous, lobes triangular-subulate, keeled, 1.3–2.8 mm; corolla pink to rose pink, with 2 yellow lines and dark purple spots in abaxial throat, 15–23 mm, throat pilose externally and villous within across bases and sinus of adaxial lobes, lobes: abaxial spreading, adaxial reflexed-spreading, 6–7(–8) mm, abaxial pilose externally, adaxial glabrous externally; proximal anthers parallel to filaments, distal perpendicular to filaments, pollen sacs 2–3 mm; style exserted, 10–16 mm. Capsules globular, 4–5(–6) mm. Seeds black, 0.6–1 mm. 2n = 28.
Phenology: Flowering late Sep–Oct.
Habitat: Wet to mesic savannas, bogs, wet prairies, borders of fresh to brackish marshes, roadsides and ditches, drier sites near these habitats.
Elevation: 0–100 m.
Ala., Fla., Ga., La., Miss., N.C., S.C., Tex., West Indies (Bahamas).
The authors have not seen specimens from southeastern coastal Virginia; Agalinis harperi is expected there. The species is known from Liberty and Newton counties, Texas.