Kalmia polifolia Wangenh.

An evergreen shrub 1 to 2 ft high, of rather thin, erect, bifurcating habit, but bushy; young shoots two-edged, covered with a fine down at first. Leaves opposite or in threes, narrowly oblong or ovate, 3⁄4 to 11⁄2 in. long, 1⁄8 to 3⁄8 in. wide, plane or recurved at the margins, tapered at both ends, dark lustrous green above and glabrous except on the midrib, lower surface glaucous white. Flowers in a terminal, flattish cluster 1 to 11⁄2 in. across, produced late in April; flower-stalks glabrous, very slender. Calyx-lobes ovate-oblong. Corolla saucer-shaped, about 1⁄2 in. across, with five broad, shallow lobes, of a beautiful pale purplish rose. Stamens of the same colour, but with brown anthers. Bot. Mag., t. 177.

Native of both eastern and western N. America; introduced in 1767. Naturally a plant of bogs and other wet places, it likes a cool, moist soil. Under the drier conditions usually given it in cultivation it is a sturdier more erect shrub than it appears to be in nature, where it is said to be straggling. It is very hardy and one of the brightest of spring-flowering shrubs of its colour.

From the Supplement (Vol. V)

[var. microphylla] – In both the revisions of Kalmia cited above this is accorded species status – K. microphylla (Hook.) Heller.

K. occidentalis Small (not mentioned in the main work) is not a distinct species but an intermediate between K. polifolia and K. microphylla. Ebinger places it under the latter as K. microphylla var. occidentalis (Small) Ebinger, while Southall and Hardin include it in K. microphylla without distinction.