This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Erect branching shrubs, with entire evergreen coriaceous leaves, alternate, opposite, or verticillate in 3's. Flowers in naked umbels or corymbs. Calyx 5-parted or 5-divided, the segments imbricated in the bud, persistent. Corolla saucer-shaped, the limbs strongly 10-keeled in the bud, 5-lobed, with 10 pouches below the limb, the keels extending from the pouches to the lobes and sinuses. Stamens 10, shorter than the corolla; anthers oblong, awnless, the sacs opening by large terminal pores; filaments erect in the bud, soon curving outward, placing the anthers in the pouches of the corolla, straightening elastically when the flower is fully expanded. Disk 10-crenate. Ovary 5-celled; ovules numerous; style slender; stigma depressed-capitellate. Capsule subglobose, obscurely 5-lobed, 5-celled, septicidally 5-valved from the summit. Seeds small, subglobose. [Dedicated by Linnaeus to his pupil, Peter Kalm, 1715-1779, who travelled in America.]
Six known species, of North America. Type species: Kalmia latifolia L. Flowers in mostly compound umbels or corymbs; twigs terete.
Leaves oblong, mostly obtuse; flowers 3 -5 broad.
Leaves glabrous beneath or nearly so.
Leaves densely puberulent beneath.
Leaves elliptic or oval, acute at both ends; flowers 8"-12" broad.
Flowers in simple terminal umbels: twigs 2-edged.
Kalmia angustifolia L. Sp. Pl. 391. 1753.
A shrub, 6'-3° high, with few nearly erect branches, and terete twigs. Leaves oblong or oblong-lanceolate, mostly opposite, or verticillate in 3's, obtuse or sometimes acute at the apex, narrowed at the base, petioled, glabrous, dark green above, light green beneath, 1'-2 1/2' long, 3"-10" wide; young twigs and petioles often slightly glandular; flowers 3"-5" broad, purple or crimson, numerous in lateral compound or simple corymbs; pedicels filiform, slightly glandular-canescent, 6"-12" long, recurved in fruit; calyx-segments ovate, acute, glandular-canescent, persistent; capsule depressed-globose, 5-lobed, canescent, 1 1/2"-2" in diameter, the apex impressed; style long-persistent.