Stems branched, 40–100 cm; branches spreading-ascending, obtusely quadrangular-ridged, glabrous or scabridulous, sometimes slightly glaucous. Leaves spreading-ascending (primary branches) to erect or ascending (secondary branches); blade narrowly lanceolate to elliptic-lanceolate, 10–40(–50) x 2–6(–7) mm, not fleshy, margins of proximalmost sometimes 3-cleft, distal entire, midvein sometimes abaxially scabrous, adaxial surface scabridulous to slightly scabrous; axillary fascicles absent, rarely developed. Inflorescences racemes, elongate, flowers 2 per node; bracts longer than pedicels. Pedicels ascending, 1–5(–6) mm, glabrous. Flowers: calyx campanulate, tube 3–5(–7) mm, glabrous, lobes lanceolate, 3–8 mm, unequal; corolla pale to dark pink, with 2 yellow lines and dark purple spots in abaxial throat, 20–32 mm, throat pilose externally and glabrous within across bases of adaxial lobes, sparsely villous at sinus, lobes: abaxial spreading, adaxial spreading-reflexed, 6–9 mm, glabrous externally; proximal anthers parallel to filaments, distal perpendicular to filaments, pollen sacs 2.5–4 mm; style exserted, 11–24 mm. Capsules ovoid-oblong, 5–9 mm. Seeds dark brown, 0.7–1.1 mm. 2n = 28.
Phenology: Flowering late Aug–early Oct.
Habitat: Moist open sites, moist prairies, margins of mesic to wet forests, fallow fields, roadsides, ditches, margins of marshes and ponds, disturbed sandy soils.
Elevation: 0–300 m.
Ala., Ark., Kans., La., Miss., Mo., N.C., Okla., Tenn., Tex.
Agalinis heterophylla is the most common species of Agalinis in Oklahoma and is common in southern Arkansas, eastern Texas, and throughout Louisiana, except the extreme southeastern portion of the state (J. E. Williams 1973; K. A. Vincent 1982). The species occurs sporadically in eastern Mississippi and is rare in Alabama, Missouri, and Tennessee. It differs from the closely related, and rare, A. calycina by wider leaves, shorter pedicels, larger corollas, and smaller capsules. It differs from A. auriculata, which has auriculate leaves, retrorse hairs on stems and branches, spikelike racemes, and ovate-lanceolate calyx lobes.