Convolvulus macounii Greene, Pittonia 3: 331. 1898

Perennials, rhizomatous. Herb­age puberulent. Stems usu­ally ascending-decumbent, some­times proximally erect, distally weakly twining-climbing, to 50–70 cm. Leaves: blade del­tate, ovate, ovate-hastate, or ovate-lanceolate, 20–60 × 15–50 mm, base lobed, lobes ± rhombic, rounded, basal sinus rounded, apex rounded to subacute. Bracts immediately subtending sepals, oval, ovate, or ovate-oblong, (12–)15–21(–27) × (8–)10–16(–20) mm, proximally flat or slightly saccate, apex usually obtuse, sometimes acute. Flowers: sepals elliptic to ovate, 12–16 mm; corolla white, (35–)40–52(–69) mm.

Flowering May–Aug. Grassy sites, including tall grass and mixed grass prairies, prairie slopes, disturbed sites, meadows, openings in woodlands, stream banks; 400–2200 m; Alta., Man., Sask.; Ariz., Colo., Idaho, Iowa, Kans., Ky., Minn., Mo., Mont., Nebr., N.Mex., N.Dak., Okla., S.Dak., Tex., Utah, Wyo.

Calystegia macounii is morphologically and geographically intermediate between C. catesbeiana and C. malacophylla and between C. malacophylla and C. spithamaea. It differs from C. sepium in habit and leaf shape; in the Great Plains area, it is most readily identifiable by its hairy herbage, C. sepium there being glabrous.