A shrub 3 to 10 ft high, forming a cluster of erect stems; young branchlets viscid and usually glabrous. Leaves viscid, ovate, or roundish oval, 1 to 31⁄2 in. long, 5⁄8 to 3 in. wide, unevenly and sharply toothed, rounded or broadly wedge-shaped at the base, mostly abruptly pointed; dark green and glabrous above, green and downy on the midrib and veins beneath; stalk about 1⁄3 in. long. Male catkins opening in April and May with the leaves, 2 to 3 in. long. Fruits 5⁄8 in. long, oval, slender-stalked, borne in loose racemes.
Native of the mountains of Central and S.E. Europe; introduced in 1820. The leaves are variable in the degree of hairiness, and forms markedly downy on both sides at maturity are named f. mollis (Beck) Hegi. Several varieties have been distinguished, based on form and size of leaf etc., of which one of the most distinct is:
var. pumila Cesati A. viridis var. brembana (Rota) Callier; A. brembana Rota; A. v. var. parvifolia Reg. – A curiously dwarfed mountain state of A. viridis, growing 1 or 2 ft high, and forming little close mounds. Adult plants have leaves 1⁄2 to 1 in. long. This dwarfed condition, however, is merely due to the climate under which it exists. A plant introduced to Kew gradually lost its dwarf character and after twenty years was no longer distinguishable from ordinary A. viridis. Found on the Swiss Alps etc.
An alder very similar to A. viridis is found in North America. By some botanists it is included in that species and by others recognised as of specific rank under the name A. crispa (Ait.) Pursh. In Bot. Mag., n.s., t. 382, the late Dr Turrill points out that there is no constant and reliable character by which the American plants may be distinguished from the European, but on the average they differ in their larger leaves on longer petioles and their larger fruits (strobiles). He considered that they should rank as a subspecies of A. viridis (subsp. crispa (Ait.) Turrill). The American green alder was first introduced in 1782. Both it and the European green alder are hardy and vigorous shrubs, of no special ornamental value, but useful for furnishing cold, damp spots.
The Siberian green alder – A. fruticosa Rupr. – is also closely allied to A. viridis, and scarcely to be differentiated from it.