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A tree 50 to 90 ft in height, with a trunk 5 to 12 ft in girth, of narrow, pyramidal habit; young shoots covered with minute glands, glutinous, not downy. Leaves broadly obovate, sometimes almost round, the base always more or less tapered, the apex rounded, and thus giving the leaf a pear-shaped outline; 11⁄2 to 4 in. long, two-thirds to about as much wide; irregularly toothed except near the base; dark lustrous green, glabrous and glutinous above; pale green and with tufts of down in the vein-axils beneath; veins in six to eight pairs; stalk 1⁄2 to 1 in. long. Male catkins opening in March, usually three to five together, each 2 to 4 in. long. Fruit egg-shaped, 1⁄3 to 2⁄3 in. long, rather numerous in the cluster.
Native of Europe (including Britain), W. Asia, and N. Africa. The common alder has not much to recommend its being brought into the garden. It is abundant in a wild state, and the genus can be more effectively represented in gardens by selected varieties and such species as A. cordata and A. nitida. It is, at the same time, a very useful tree for planting in boggy places where few trees would thrive. The timber was once chiefly employed in the manufacture of the clogs so commonly used in the Lancashire mill towns. An ancient and humble, but honourable form of woodcraft was carried on where alders abound, especially in the north, by men who travelled from place to place, purchased the alder trees standing, felled them, then cut up the timber and roughly shaped it on the spot for clog-making.
There is a remarkable specimen of the common alder at Sandling Park, Kent, measuring 86 × 121⁄4 ft, with a smooth, round bole 45 ft in length to the first branch (1965).
Both A. glutinosa and A. incana (q.v.) are remarkable for the large number of cut-leaf forms which they have produced. These seem to be particularly common in Scandinavia and are reviewed by Nils Hylander in Svensk Botanisk Tidskrift, Vol. 51, part 2, 1957, with twenty-eight plates showing the extraordinary range of leaf-cutting that has been observed. The cultivated forms are also treated.
The remarkable tree at Sandling Park, Hythe, Kent, now measures 95 × 13 ft (1980). Some others noteworthy for height or girth are: Flitwick Manor, Beds., 70 × 13 ft (1977); Christchurch Park, Ipswich, with a fine bole, 87 × 71⁄4 ft (1981); Ashburnham Park, Sussex, 105 × 73⁄4 ft (1983); Old Roar Ghyll, St Leonards, Sussex, 98 × 51⁄4 ft (1981).
A. g. var. incisa Willd
Similar to ‘Imperialis’, but not so deeply and narrowly lobed; lobes not toothed. In his review of the cut-leaf alders, Hylander accepts the statement made by Thouin (1819), and quoted by Loudon, that all the plants of this form descend from one grown in a garden near St Germain, ‘where the stool still remains from which all the nurseries of Paris have been supplied with plants, and, probably all Europe’. It makes a tree of some size, and reached 70 ft at Syon Park, Middlesex.It has been confused with f. incisa, but in that group the leaves are small and of rounded outline, with toothed lobes, whereas in ‘Laciniata’ the leaves are oblong and the lobes pointed and untoothed.