Alnus glutinosa (L.) Gaertn.

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.

cv. ‘Aurea’. – Leaves golden yellow. Raised in Vervaene’s nursery, Ledeberg-les-Gand, about 1860. Not so vigorous as the type.

var. barbata (C. A. Mey.) Ledeb. A. barbata C. A. Mey. – Leaves oval or ovate, rounded at the base and either rounded or pointed at the apex, doubly toothed; 2 to 31⁄2 in. long, 11⁄2 to 21⁄2 in. wide; dark glossy green above, downy beneath, especially on the veins and midrib; veins in eight to ten pairs; stalks 1 to 3⁄4 in. long, downy. Native of the Caucasus and the mountains of Persia. It is distinguished from the type by the hairy shoots and leaves, and in the often pointed apex of the latter. It is represented at Kew by some small plants, the tree 30 ft by the lake, mentioned in previous editions, having died long ago.

cv. ‘Imperialis’. – Leaves deeply and pinnately lobed, the lobes lanceolate, slender, pointed, not toothed, reaching more than half-way to the midrib; stalks 1 to 11⁄2 in. long. Often a thin, rather ungainly tree, never of great size. A well-known garden clone, in cultivation since before 1859.

f. incisa (Willd.) Koehne A. g. var. incisa Willd. – Leaves small, usually less than 1 in. long, rounded or ovate in outline, deeply cut into broad, toothed lobes, or even right to the midrib. The plant once grown at Kew made a dwarf, compact bush and was probably of the clone distributed by Loddiges’ Hackney nurseries, and by Booth’s nurseries, Hamburg, Germany, as A. glutinosa oxyacanthifolia – the thorn-leaved alder. A form with similar leaves, but making a large shrub or small tree, has also been described and may represent a different clone. Elwes and Henry mentioned such a one at Barton, near Bury St Edmunds, 44 ft high and 2 ft 8 in. in girth.

The name A. glutinosa incisa has also been used, wrongly, for the clone ‘Laciniata’ (q.v.).

cv. ‘Laciniata’. – 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.

f. pyramidalis (Dipp.) Winkler – Branches erect. ‘birkiana’ is a clone of this character, once distributed by Späth’s nurseries.

f. quercifolia (Willd.) Koehne – Upper part of the leaves with triangular, toothed lobes, the deepest not reaching more than one-third of the way to the midrib. Plants of this form were distributed early in the nineteenth century by Loddiges’ nursery and are also found wild in Scandinavia.

cv. ‘Rubrinervia’. – Leaves with red veins and stalks.

cv. ‘Sorbifolia’. – Leaves oblong or oval, deeply cut into about six pairs of lobes, which are oblong and coarsely round-toothed, the sinuses often widest at the base. One of the most distinct of the cut-leaved sorts. The tree itself is not a strong grower, and is of rather lax habit. The plant described is almost certainly of the same clone as the one to which Dippel gave the name A. g. var. sorbifolia in 1892. Similar forms are found wild in Scandinavia and the group name for them all is f. lacera (Mela) Mela (Hylander, op. cit.).

A. × pubescens Tausch – A group-name for hybrids between A. glutinosa and A. incana, which are found fairly commonly where the two species meet. According to P. W. Ball in Flora Europaea, Vol. 1 (1964), such hybrids are usually characterised by downy young growths, leaves downy beneath, at least on the veins, blunt or shortly acuminate at the apex, and the female catkins shortly stalked (in the first parent they are stalked and in the second sessile).

From the Supplement (Vol. V)

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).