Great Laurel
or
Rosebay
Rhododendron maximum
From Rosebay.org
In the central and southern regions forms dense thickets which in pioneer days caused travel across the Appalachian and Allegheny mountains to be very difficult.
The epithet 'maximum' refers to the large size of a mature specimen which although normally 15 feet, may become tree-like reaching 40 feet. The plant habit is spreading, broader than tall. The handsome leaves are large, 4 to 12 inches long, glossy dark green, and thinly indumented. The branchlets, petioles, and flower parts are glandular. These glands are quite apparent on the new growth causing it to feel sticky to the touch. 
The inflorescence (truss) of 15-30 funnel-shaped flowers is presented in a upright candelabroid umbel. The 5-lobed flower is 1 inch long, white to pale pink, occasionally deep pink to rose red in color with yellow-green spotting. Bloom time is late-season with peak being mid-July in northern locations. Hardiness is rated at -15° to -20° F (-25° to -29° C).
Rhododendron maximum, The Rosebay Rhododendron, is the only elepidote (having no scales) species native to New England. It grows in woods, often in dense shade, from sea level to 6000 feet in eastern North America from Georgia to Quebec and Nova Scotia. Growing along streams and on moist, rocky wooded slopes, it tolerates the low pH associated with damp, shady almost bog-like conditions. Rhododendron State Park in USDA Zone 4, Fitzwilliam, New Hampshire contains a large stand of this species.