Betula pumila L.

Erect in habit, the North American Betula pumila is the ecological analogue of Eurasian B. humilis, occurring in bogs and on the fringes of lakes or bordering creeks; it appears to be the only regularly tetraploid birch species in North America. In the wild it is probably much confused with B. glandulosa of drier habitats, from which it is distinguished by the often densely hairy and usually stiffer twigs with persistent coarse crisped hairs (≥0.5 mm and longer, against 0.05 mm with few longer silky hairs in B. glandulosa), coarser and sharper leaf teeth, shorter male catkins, and the arrangement of catkins with lateral males below females. In cultivation it could be mistaken for B. humilis, but is more vigorous, with stouter twigs, bigger buds and more-or-less obovate leaves. The typical form – with hairy twigs and leaves that soon become eglandular – is more or less confined to the northeastern corner of North America, perhaps as relatively isolated populations. However, populations of less hairy shrubs with more persistently glandular leaves occur sporadically in wet habitats across North America to Vancouver Island (Dugle 1966).

Betula pumila is never as neat and elegant as B. humilis can be at its best, and its rather sparse, open, straggly habit makes it a poor garden subject, at least in western Europe. However, on wet soils it may form quite a neat bush if pruned; the crimson-tipped female flowers can be conspicuous in the spring, and the autumn foliage colour is attractive. Like many plants of wet, open habitats it is very intolerant of shade, only growing well in full sun. It has grown happily in north Devon in well-drained, poor soil, forming a shrub 2 m tall in ten years, flowering and fruiting freely.