A. serrulàta.
2. Álnus serrulàta, Willd. (Smooth Alder.) Leaves 2 to 4½ in. long, thickish, obovate, acute at base, sharply and finely serrate, green both sides, smooth or often downy beneath; stipules yellowish green, oval, and falling after 2 or 3 leaves have expanded above them. Fruit ovate. Rather a shrub than a tree, 6 to 12 ft. high, common along streams south of 41° N. Lat. In the Southern States it sometimes forms a tree 30 ft. high.
A. marítima.
3. Álnus marítima, Muhl. (Seaside Alder.) Smooth; leaves oblong-ovate to obovate, with a tapering base, sharply serrulate; petiole slender; color bright green, somewhat rusty beneath. Flowering in the autumn. Fruiting catkin large, ¾ to 1 in. long, ½ in. thick, usually solitary, ovoid to oblong. A small tree, 15 to 25 ft. high. Southern Delaware and eastern Maryland, near the coast.
A. glutinòsa.
4. Álnus glutinòsa, L. (European Alder.) Leaves roundish, wedge-shaped, wavy-serrated, usually abrupt at tip, glutinous; sharply and deeply incised in some varieties. Fruit oval, ½ in. long. A medium-sized tree, 25 to 60 ft. high, of rapid growth, often cultivated under several names; the most important being vars. laciniata (cut-leaved), quercifolia (oak-leaved), and rubrinervis (red-leaved).
A. cordifòlia.