Trees or shrubs with alternate stipulate leaves. Flowers monoecious. Male flowers in drooping catkins, sepals 4 or less, stamens 2-4; female flowers 2-3, under each scale of a catkin; perianth o. Fruit indehiscent.

A large family chiefly found in the temperate regions.

Betula L

Stamens 2; scales of female catkin thin, deciduous, trifid.

Betula Nana L. Dwarf Birch

A small dwarf shrub. Leaves very shortly stalked, nearly orbicular, about 1/2 inch long, very obtuse, crenate or serrate. Catkins small and sessile, the males oblong, the females very short, erect.

Moors and bogs in the Alps and sub-Alps up to 6500 feet. May, June.

Distribution

Central and Northern Europe, Northern Asia and Arctic America. British.

Betula Pendula Roth. (B. Alba L.). Silver Or Common Birch

A small tree, 40-50 or rarely 70 feet high, with white papery bark and glabrous ovate-acuminate, doubly serrate leaves. Fruit broadly winged.

Woods, marshes, and hills, up to the superior limit of the Beech. April, May. In Scandinavia to the upper limit of Pines.

Distribution

Europe, temperate and Arctic Asia; N. America (a variety).

Betula Pubescens Ehrh

A similar tree with narrower pointed leaves which are pubescent and finally only downy at the midrib. Fruit broadly winged.

Damp woods, peat-bogs and moors in the plains, sub-Alps and Alps. April, May.

Distribution

Switzerland, Jura, Alps, Pyrenees; Central and Northern Europe, Caucasus, Northern Asia, Greenland.

Alnus L. Alder

Stamens 4. Scales of female catkin persistent, woody.

Alnus Viridis Dc. Green Alder. (Plate XVIII)

A shrub sometimes attaining the height of a small tree in the lower mountains. Leaves stalked, green, ovate-acute, doubly serrate, glabrous. Flowers in monoecious catkins, male cylindrical, drooping; female oval, stalked, 2-5 in erect racemes, not 1/2 inch long, forming a woody cone ripening the second year.

Mountains and clearings in the lower Alps, from 3000 to 6600 feet, especially abundant on granite and schist.

Distribution

Central and Eastern Europe, Northern Asia and America.

Alnus Incana Medik

A shrub or tree with silvery bark and oval-acute leaves doubly serrate, glabrous above, downy and grey beneath. Fruit not winged.

Damp woods, borders of streams, etc., up to 5000 feet. March, April.

Distribution

Alps, Jura; Europe, temperate Asia, N. America.

Alnus Glutinosa L. Common Alder

This well-known tree has obtuse, almost orbicular leaves, which are shortly petioled and sticky at first on the upper side. Damp woods, by water, etc., up to 4000 feet. February to April.

Distribution

Europe, temperate Asia, N. Africa. British.