Stems simple or branched, 10–50(–60) cm; branches ascending, sharply quadrangular, siliceous ridges and/or wings on angles distally, scabrous or scabridulous mostly on angles, especially proximally. Leaves: proximal slightly spreading, distal ascending-appressed; blade linear, 5–20(–25) x 0.5–1.5 mm, not fleshy, margins entire, abaxial midvein scabrous, adaxial surface scabrous; axillary fascicles absent. Inflorescences racemes, flowers 2 per node on central terminal raceme; bracts both longer and shorter than, or shorter than, pedicels, secondary branches with shorter pedicels, bracts shorter than pedicels. Pedicels erect-ascending, (3–)5–17(–30) mm, glabrous or sparsely scabridulous. Flowers: calyx hemispheric, tube 2–4.5 mm, glabrous, lobes triangular-subulate, 0.3–1.2 mm; corolla whitish to pale pink or pink, with 2 pale yellow lines and red spots in abaxial throat or lines absent, 8–16 mm, throat pilose externally and villous within across bases and sinus of adaxial lobes, lobes: abaxial spreading, adaxial spreading to reflexed, 3–4 mm, glabrous externally; proximal anthers parallel to filaments, distal perpendicular to filaments, pollen sacs 0.6–1.2 mm; style exserted, 4–8 mm. Capsules globular, 3.5–5 mm. Seeds yellow, 0.6–1 mm. 2n = 26.
Phenology: Flowering Aug–early Oct.
Habitat: Dry to mesic areas in sand and loess hill prairies, bluff prairies, dolomite glades, dunes, open woods, areas of low and/or sparse herbaceous cover.
Elevation: 10–300 m.
Ont., Ark., Ill., Ind., Iowa, Kans., La., Md., Mich., Miss., Mo., Ohio, Wis.
Agalinis skinneriana is rare throughout its relatively wide range. Specimens of A. skinneriana are often misidentified as A. gattingeri or A. tenuifolia, which also have elongated pedicels. Characters that differ between A. gattingeri and A. skinneriana are given in the discussion of 14. A. gattingeri. Although A. skinneriana and A. tenuifolia both have low wings on the stem angles, the flowers of the two species differ. The corolla throat is villous within at the bases of the reflexed adaxial lobes in A. skinneriana, while the corolla throat is glabrous within at the bases of forward-projecting adaxial lobes of A. tenuifolia. The abaxial corolla lobes are glabrous externally in A. skinneriana, but the abaxial lobes of A. tenuifolia are pilose externally. The main stem on plants of A. skinneriana is often simple or has few branches, and the leaves are strongly ascending to appressed on secondary branches. Stems of A. tenuifolia are usually much branched and the leaves are spreading, arching, or reflexed, sometimes ascending, but not appressed. Plants of A. tenuifolia may have axillary fascicles; fascicles are absent in A. skinneriana.
Agalinis skinneriana is in the Center for Plant Conservation’s National Collection of Endangered Plants.