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 mostly tall branching shrubs, with alternate thin deciduous leaves. Flowers large, white, purple, yellow, pink, or orange, in terminal umbels developed from cone-like scaly buds. Calyx small or minute, 5-parted. Corolla funnelform, the tube mostly narrow, the limb nearly regularly 5-lobed or somewhat 2-lipped. Stamens 5 (rarely 10), exserted, usually declined; anthers awnless, attached to the filaments by their backs, the cells opening by terminal pores; styles slender, declined, exserted. Ovary 5-celled; ovules numerous in the cavities. Capsule oblong or linear-oblong, 5-celled, septicidally 5-valved from the summit, many-seeded. [Greek, dry, from the habitat of one of the original species.]
About 40 species, natives of North America and Asia. Besides the following, another occurs on the Pacific Coast and 2 or 3 in the Southern States. Type species: Azalea indica L. The genus is included in Rhododendron by some authors. Flowers expanding before or with the leaves.
Flowers pink or white.
Leaves strigose on the midrib beneath; corolla-tube hirsute.
Leaves canescent beneath; corolla-tube glandular.
Flowers orange, yellow or red; leaves canescent beneatlu
Flowers expanding later than the leaves.
Leaves shining, glabrous beneath.
Leaves strigose on the midrib beneath.
Azalea nudiflora L. Sp. Pl. Ed. 2, 214. 1762.
R. nudiflorum Torr. Fl. N. & Mid. U. S. 424. 1824.
A shrub, 2°-6° high, branched above, often simple below, the twigs glabrous, or with stiff hairs. Leaves oblong or obovate, acute at both ends, short-petioled, hairy on the midrib and sometimes on the lateral veins beneath, glabrous or with a few scattered hairs above when old, sometimes canescent on the lower surface when unfolding, 2-4' long, the margins ciliolate; pedicels strigose, 4"-7" long; flowers pink to nearly white, expanding before or with the leaves, faintly odorous, the limb somewhat 2-lipped, 1 1/2' 2' broad, shorter than the narrow tube, which is pilose-pubescent and little or not at all glandular; stamens much exserted; capsule linear-oblong, strigose, 8"-9" long, erect.
In dry sandy or rocky woods and thickets Massachusetts to Illinois, south to Florida and Texas. Ascends to 3000 ft. in Virginia. Reported from Canada and from Maine. Swamp or election-pink. Mayflower. Early, purple or swamp-honeysuckle. River-pink. April-May.