Clethra alnifolia is a shrub 1-3 m tall, habit erect, extensively clonal from root sprouts, multistemmed, branches slender and sinuous, bark dark gray, smooth, finely grainy, propagates mainly by clonal spread rather than seed (Jordan and Hartman, 1995); twigs densely pale wooly, hairs star-shaped (use lens); leaf scar U-shaped, with a single protruding, V-shaped vein (bundle) scar (Seiler 2007; Harlow 1946).
Leaves alternate, stalk short, finely wooly-hairy, blade 4-11 cm long, 2-5 cm wide, mostly widest above middle (oblanceolate), tip pointed, base gradually tapered to stalk; veins pinnate, conspicuous, slightly impressed above, secondary veins parallel and at an acute angle to midrib; margin sharply toothed except near base; autumn foliage yellow-brown.
Flowers white, radially symmetrical, about 0.8 cm wide (Scheper 2007), very fragrant, petals 5, 0.5-0.8 cm long, tips rounded, sepals 5, 0.2-0.4 cm long, densely wooly, persistent in fruit (use lens); stamens 10 longer than petals, anthers becoming dark; ovary superior, 3-parted, style much longer than petals, stigmas 3, persistent in fruit; inflorescence of spike-like clusters (racemes) at ends of stems; blooms July-Aug.; very attractive to bumble bees and some wasps (Gargiullo personal observation).
Fruit dry, a grayish, rounded 3-lobed, hairy capsules 0.2-0.3 cm long, partly enclosed by persistent sepals, capsule splitting open in three sections to release pale tan, translucent seeds 0.1 cm long, surface puckered (Radford et al. 1968), wind dispersed in winter; dry fruit persistent through winter.
Wetland status: FAC+.
Frequency in NYC: Frequent.
Habitat: Moist to wet understories of undisturbed forest. Often a dominant of shrub. Also planted in wetland restorations. Tolerant of acid soil, pH 4.5-7 (Hightshoe 1988; USDA, NRCS 2006). Found in forest soil pH 4.4-5.0 (Gargiullo unpublished data).Tolerant of salt, soil compaction, flooding (brief), saturated soil for up to 25% of growing season, moderately tolerant of shade in closed canopy forest but blooms and establishes seedlings better in gaps and edges (Jordan and Hartman 1996); intolerant of drought (Hightshoe 1988).
Notes: Twigs eaten by rabbits and deer (Martin et al 1951). Seeds eaten by goldfinches and probably by other small birds (Gargiullo pers. obs.).