This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Trees and shrubs in which the fleshy scales of the persistent cone-like female catkins become indurated and ligneous as they approach maturity. Stamens 3 to 5. This genus has about the same range in the northern hemisphere as the last, and extends to South America. The ancient Latin name of the genus.
1. A. glutinosa. Alder. - This is the only native species. It is usually a shrub or small tree, though it occasionally attains a height of 50 to 70 feet, and it abounds in the vicinity of rivers and brooks. The ordinary variety may be distinguished by the black bark, glutinous branches, and young leaves, which are of an orbicular or obovate form with a wavy serrulate margin. The female catkins are borne in racemes, and persist during the winter. The variety aurea has golden foliage, and imperialism laciniata, asplenifolia and quercifolia, have more or less lobed or cut foliage; the first having elegant drooping branches and fern-like leaves. This species occurs throughout Europe, North Africa, and North Asia.
2. A. cordifolia. - A very distinct South European species, having more the aspect of a Poplar, the leaves being nearly or quite glabrous, and somewhat shining, ovate or oblong-cordate in outline, with a serrate margin. It is a fast-growing tree with light-coloured bark.
A. incana and A. semdata are North American species, of no especial interest to horticulturists.