Flora of New Zealand Series

silver birch

Tree to c. 25 m high; branchlets slender, often semi-drooping. Bark smooth at first, silvery-white and papery, usually becoming dark grey and rough at least on lower trunk. Shoots glabrous, ± glandular-resinous, prominently lenticellate and appearing warty. Petiole slender, mostly 7-25 mm long. Lamina 3-6 × 1.5-5.5 cm, deltoid, ovate or rhombic-ovate, glabrous, with 5-7 pairs of veins, glandular-resinous when young, coarsely and doubly serrate; base subcordate, truncate or broadly cuneate; apex acuminate. ♂ catkins 2-9 cm long; bract 2-3 mm long, shield-like, both bract and bracteoles ciliolate. ♀ catkins 1.5-2.5 cm long, scarcely elongating at fruiting but becoming broadly cyclindric and c. 0.7 cm wide. Stigmas rose. Scales 3.5-4.5 × 4-5 mm, puberulent; lateral lobes broader and rounder than middle lobe, widespreading and often ± downward curving. Fr. 1.5-2.5 mm long; wing much > fr.

N.; S.: occasional throughout, most common in inland and E. parts of the South Id.

Europe, W. Asia, Asia Minor, Morocco 1880

Open modified areas in and around settlements and sometimes further afield.

FL Sep-Nov.

Silver birch has probably been even more commonly planted in N.Z. than pedunculate oak, Quercus robur, particularly in the coldest areas where it is often the most abundant tree in parks, gardens and streets. The light wind-dispersed frs with bracts (Fig. 38) germinate very readily and spontaneous plants grow on almost any disturbed ground, sometimes so freely that they are troublesome. There is a considerable range of form in cultivation, some trees having a much more graceful, pendulous habit than others, and there are also differences in colour and roughness of bark. The sp. has previously been known in N.Z. as B. alba, and B. verrucosa.

Recently B. papyrifera Marsh has been commonly planted, but has not been reported wild, although it also seeds freely. This is the N. American canoe birch which has a thicker, white bark, persistent almost to the base; the young shoots and lvs are hairy. The European B. pubescens Ehrh., downy birch, is also cultivated and has hairy lvs and young shoots, but has a brownish or grey bark. It may have sometimes been planted mistakenly for B. pendula. All these spp. have lvs which turn yellow in autumn.

Fig. 38. Betula pendula, A bract, B fr. © All rights reserved. [Image: 4X4W]