J. Bot. Res. Inst. Texas 4: 1, fig. 1. 2010.
Stems branched, 30–90 cm; branches spreading-ascending, larger branches widely spreading and decumbent-ascending, quadrangular, glabrous or scabridulous on angles. Leaves spreading to spreading-ascending; blade linear to linear-spatulate, 7–13 x 0.8–1.5 mm, margins entire, midvein scabrous; axillary fascicles absent. Inflorescences paniculate-racemiform, flowers 1 or 2 per node; bracts shorter than pedicels. Pedicels spreading, 4–20 mm, glabrous. Flowers: calyx elongate-campanulate, tube 2–3.2 mm, glabrous, lobes deltate-subulate, 0.2–0.5 mm; corolla pink to rose, without 2 yellow lines and sometimes with dark-pink spots in abaxial throat, (8–) 10–12 mm, throat pilose externally and villous within across bases and sinus of adaxial lobes, lobes: abaxial spreading, adaxial reflexed-spreading, 3–4.5 mm, glabrous externally; proximal anthers parallel to filaments, distal perpendicular to filaments, pollen-sacs 1.2–1.8 mm; style exserted, 5–7 mm. Capsules obovoid-oblong, 3.8–4.5 mm. Seeds golden brown, 0.5–0.6 mm.
Phenology: Flowering Sep–late Oct.
Habitat: Mesic to moist soils, open, wiregrass-dominated longleaf pine systems, savannas, prairies, seepage slopes, depressed wetlands, disturbed ground.
Elevation: 0–60 m.
Agalinis flexicaulis is of conservation concern because of its limited distribution. The species is currently known from Bradford County.
Plants of Agalinis flexicaulis are distinguished by their weakly ascending main branches, which become more drooping and lax as they mature. It is most easily confused with the more widespread A. obtusifolia and A. tenella. Agalinis flexicaulis is differentiated from these species by characters in the key.