Stems often leaning, branched, 30–70 cm; branches ascending to widely spreading, subterete proximally to obtusely quadrangular distally, glabrous or scabridulous. Leaves alternate, spreading; blade filiform, widened slightly distally, 10–20(–30) x 0.2–0.6(–1) mm, fleshy, margins entire, adaxial surface sparsely scabrous; axillary fascicles often equal to or longer than subtending leaves. Inflorescences racemes, elongate, flowers 1 or 2 per node; bracts shorter than pedicels. Pedicels spreading-ascending, 9–33 mm, glabrous. Flowers: calyx campanulate, tube 3–5 mm, glabrous, lobes subulate, 0.3–1.5 mm; corolla dark pink to nearly rose, with 2 yellow lines and purple spots in abaxial throat, 15–30 mm, throat pilose externally and villous within across bases and sinus of adaxial lobes, lobes: abaxial spreading, adaxial reflexed-spreading, 5–10 mm, pilose externally; proximal anthers parallel to filaments, distal perpendicular to filaments, pollen sacs 2.5–3.7 mm; style exserted, 10–20 mm. Capsules globular, 3.9–5.3 mm. Seeds nearly black, 0.4–0.5 mm. 2n = 28.
Phenology: Flowering Jun–Nov.
Habitat: Xeric, sandy, open pine forests, open coastal scrub habitats, dunes, open areas of pine flatwoods, hydric soils of pine flatwoods.
Elevation: 0–30 m.
Ala., Fla., Ga.
Agalinis filifolia is largely a species of Florida, where it is found in xeric, open, sandy, upland sites throughout the state. The species will, however, tolerate hydric conditions in open, pine flatwoods of southeastern Florida and is more common in south-central Florida than in any other part of its range. In the southernmost portion of its range, it flowers from early June through November, with different populations showing distinct phenologies. Agalinis filifolia is uncommon to rare in the Florida Panhandle and in southeastern Georgia, reaching its westernmost distribution along the remaining coastal scrub habitats of southern Baldwin County, Alabama.