Betula L.

1. Betula L. View in CoL 3

Trees or shrubs. Catkins with 2 bracteoles to each group of flowers in the axil of a bract. Male flowers with 2 stamens, bifid from below the anthers; perianth minute. Female flowers 3 to each bract. Fruiting catkins cylindrical or narrowly ovoid; scales three-lobed, falling with fruit.

The taxonomy of European Betula is much disputed. The following treatment does no more than provide a minimum framework. For more detailed study the bibliography provided by Natho is very useful.

B. papyrifera Marshall , Arbust. Amer. 19 (1785) from North America, a tree up to 40 m, with ovate, subglabrous leaves 4- 10 cm, and catkin-scales with suberect lateral lobes, is sometimes planted.

Literature: P. Ascherson & K. O. P. P. Graebner, Syn. Mitteleur. Fl.4~. 386-412 (1910). G. Natho, Feddes Repert. 61: 211-73 (1959). K. H. Rechinger in Hegi, III. Fl. Mitteleur. ed. 2, 3 (1): 141-73 (1957). H. Winkler in Engler, Pflanzenreich 19 (IV. 61): 56-101 (1904).

1 Trees or large shrubs, usually more than 3 m; young male catkins in winter pendent and unprotected

2 Young twigs glabrous, with numerous peltate resin-glands; leaves usually sharply biserrate with prominent primary teeth; nutlet glabrous 1. pendula

2 Young twigs without resin-glands, often hairy; leaves irregularly serrate, without prominent primary teeth; nutlet puberulent at apex 2. pubescens

1 Small shrubs up to 3 m; young male catkins in winter erect, protected by bud-scales 3 Leaveslongerthan broad,acuteor subacute 3. humilis 3 Leavesmoreor lessorbicular,obtuseor truncate 4. nana