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Tim Baxter & Hugh A. McAllister (2021)
Baxter, T. & McAllister, H.A. (2021), 'Alnus incana' from the website Trees and Shrubs Online (treesandshrubsonline.
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A tree 60 to 70 ft high, with a trunk occasionally 6 ft. in girth; young shoots covered with a short, grey down. Leaves ovate, oval, or occasionally obovate, rounded or wedge-shaped at the base, and with short, abrupt points; 2 to 4 in. long, 11⁄4 to 21⁄4 in. wide; the margins with six or more coarse teeth about the middle, these again being sharply toothed, the base entire; upper surface dull green covered with flattened down when young, lower surface grey with a close down, at least when young; veins in nine to twelve pairs; stalk 1⁄2 to 7⁄8 in. long, covered with minute down. Male catkins 2 to 4 in. long, usually three or four in a cluster, opening in February. Fruits ovoid, numerous, and rather densely clustered, 1⁄2 to 5⁄8 in. long.
Native of Europe and the Caucasus, not of Britain, but introduced in 1780. This alder is an exceptionally hardy tree, and useful for planting in cold, wet places. With the exception of A. glutinosa, it is the commonest of alders, but is more frequently represented in gardens by the various cut-leaved and coloured forms than by the type. From A. glutinosa in all its forms it is most obviously distinguished by the grey downy leaves and young shoots. The typical A. glutinosa is, of course, very distinct in the obovate, round-ended leaves, green and almost glabrous beneath.
The American form of A. incana, long known as A. incana var. americana, is now placed under A. rugosa (q.v.).
Regarded in a wide sense, this species is circumpolar in distribution. See further below under A. rugosa and A. tenuifolia.
The grey alder has attained 92 × 41⁄4 ft at Castle Milk, Dumfries (1984). It was planted in 1928.
cv. ‘Aurea’. – The most decorative feature of the golden grey alder is the brightly coloured young male catkins, which start to redden even before the leaves have fallen.
Small tree to 12 × 6m spread. Identified by the leaves yellowish, especially the new foliage, and downy beneath. Bark and new shoots orange and remaining so through the winter. Catkins remain on tree all winter and remain attractive orange to pink. Slower growing than the species and a useful amenity tree.
Branches weeping. Van der Bom’s nursery, Holland, before 1903. Originally distributed as A. i. pendula nova.