Trunks and branches terete. Bark thin, close or exfoliating in thin sheets, becoming thicker and frequently furrowed or broken in age; lenticels often present, prominent, sometimes becoming greatly expanded horizontally. Bark and wood strongly tanniferous. Young twigs and buds often covered with small to large, resinous glands; pith triangular in cross section. Leaves 3-ranked, occasionally nearly 2-ranked. Staminate flowers: perianth of 4(–6) sepals, well defined, minute, membranaceous. Pistillate flowers 2–3 per scale, scales arranged in conelike catkins; perianth not obvious; ovules with 1 integument. Infructescences 1–4 cm, conelike, composed of many scales; scales either persistent or deciduous with fruits, crowded, small, woody or leathery. Fruits tiny samaras, lateral wings 2, membranous, sometimes reduced to ridges; pericarp thin, leathery.

Distribution

Primarily boreal and cool temperate zones of Northern Hemisphere

Discussion

Genera 2, species 60 (2 genera, 26 species in the flora).

Selected References

None.

Lower Taxa

Alnus, Betula