A dwarf, neat-habited bush 2 to 4 ft high, branches erect, not warted, clothed the first two years with minute down. Leaves round or occasionally broader than long, never pointed, 1⁄4 to 1⁄2 in. diameter, conspicuously round-toothed except at the base; shining dark green above, prettily net-veined beneath, glabrous on both surfaces; veins in two to four pairs; stalk 1⁄12 in. or less long, with a fringed stipule at each side. Fruiting catkins erect, 1⁄3 in. long, shortly but distinctly stalked; scales glabrous, with lobes of about equal length, the middle one the broadest.
Native of northern latitudes in Europe (including N. Britain) and N. America, usually inhabiting moist places on mountains. In gardens it is useful for planting on the margins of streams and in moist places generally. Among shrubby birches it is distinguished by its round-toothed, orbicular leaves, and the absence of warts or glands on the shoots.
B. × intermedia Thomas B. alpestris Fries. – Hybrids between B. nana and B. pubescens. In the typical form the leaves are larger than in B. nana, and more ovate, but retain much of the characteristic toothing of that species. Such hybrids are found in many parts of Europe where the two species are in contact.
From the Supplement (Vol. V)
† cv. 'Walter Ingwersen'. – A very dwarf form, collected by Walter Ingwersen at Narvik, Norway. A mature plant will be only 9 in. or so high and somewhat more in spread. It received an Award of Merit when shown by Messrs Ingwersen in 1978 (A.G.S. Bull., Vol. 46, p. 295 (1978)).
The North American representative of B. nana differs from it in some characters and is now usually treated as a distinct species – B. michauxii Spach (B. nana var. michauxii (Spach) Reg; B. terrae-novae Fern.). It is a native of north-eastern Canada. The western limit of B. nana as now understood lies in Greenland.
A dwarf birch in Alaska sometimes referred to B. nana is now considered to belong to B. exilis Sukachev, which has its main distribution on the other side of the Behring Strait.