Stems branched, 15–72 cm, bushy; branches spreading-ascending, terete to quadrangular proximally, quadrangular-ridged distally, glabrous or sparsely scabridulous. Leaves spreading or arching; blade filiform to sometimes narrowly linear, 10–45 x 0.2–1(–1.5) mm, not fleshy, margins entire, abaxial midvein occasionally scabridulous, adaxial surface finely scabrous; axillary fascicles absent or shorter than subtending leaves. Inflorescences racemes, sometimes interrupted by floriferous branches, flowers 2 per node; bracts shorter than or nearly equal to pedicels. Pedicels ascending-spreading, (5–)10–35 mm, glabrous. Flowers: calyx turbinate-obconic, tube 2.2–4.4 mm, glabrous, lobes triangular-subulate, 0.3–0.9 mm; corolla pink to rosy pink, with 2 yellow lines and red spots in abaxial throat, (9–)13–22 mm, throat pilose externally and villous within across bases and sinus of adaxial lobes, lobes: abaxial spreading to reflexed, adaxial reflexed, 3.5–7 mm, pilose externally throughout or only proximally; proximal anthers parallel to filaments, distal perpendicular to filaments, pollen sacs 2–3.2 mm; style exserted, 8–15 mm. Capsules elliptic-ovate, 3–4 mm. Seeds black, 0.4–0.7 mm. 2n = 28.
Phenology: Flowering Aug–Oct.
Habitat: Dry sandy soils, pine savannas, margins of pine-oak woodlands and scrub, sand hills, roadside embankments.
Elevation: 0–500 m.
Ala., Del., D.C., Fla., Ga., Md., N.J., N.Y., N.C., S.C., Tenn., Va.
Agalinis setacea is most common in North Carolina, South Carolina, and Virginia, and is much more rare or localized in other states.
Agalinis setacea is largely replaced toward the south and west on the coastal plain by A. plukenetii. Plants similar to A. setacea but with more slender leaves and stems, longer internodes, and racemes similar to those in A. plukenetii occur from the mid-western peninsula of Florida near Tampa east to Lake Wales area south to Sebring. F. W. Pennell (1920, 1929) referred these plants to A. stenophylla Pennell. That species may warrant recognition based on the examination of specimens from Tampa and along the Lake Wales Ridge.