BETULACEAE

BIRCH FAMILY

John O. Sawyer, Jr.

Tree, shrub, monoecious
Stem: trunk < 35 m; bark ± smooth; lenticels present
Leaves simple, alternate, petioled, deciduous; stipules deciduous; blade ovate to elliptic, generally serrate, ± doubly so
Inflorescence: catkin, generally appearing before leaves, often clustered; bracts each subtending 2–3 flowers and 3–6 bractlets
Staminate inflorescence pendent, ± elongate
Pistillate inflorescence pendent or erect, developing variously in fruit (see key to genera)
Staminate flower: sepals 0–4, minute; petals 0; stamens 1–10; pistil vestigial or 0
Pistillate flower: sepals 0–4; petals 0; stamens 0; pistil 1, ovary inferior, chambers 2, each 1-ovuled, stigmas 2
Fruit: nut or nutlet, sometimes winged, subtended or enclosed by 1–2 bracts
Genera in family: 6 genera, 105 species: generally n hemisphere; some cultivated.

BETULA

BIRCH

Tree, shrub
Stem: trunk < 30 m; bark smooth or scaly, aromatic, often peeling in thin layers; twigs puberulent, glandular, or both; lenticels prominent; winter buds sessile, 3-scaled
Leaf glandular-hairy; blade 2–5 cm, widely elliptic, base ± truncate to tapered
Staminate inflorescence 2–7 cm; bracts each subtending 3 flowers and 3 bractlets
Pistillate inflorescence 2–3 cm; bracts each subtending 3 flowers and 3 bractlets
Staminate flower: sepals 4; stamens 2
Pistillate flower: sepals 0
Fruits many, in a non-cone-like catkin, winged; bracts lobed, papery, released with but not attached to fruit
Species in genus: 50 species: circumboreal
Etymology: (Latin: birch)
Important wildlife food; wood used for interior finishing; many species cultivated.

Native

B. occidentalis Hook.

WATER BIRCH

Tree, shrub
Stem: trunks < 10 m; bark black, red-brown, not peeling; twigs with large resin glands, hairy
Leaf: petiole < 15 mm, hairy; blade 2–5 cm, widely ovate, thin, glands especially on upper surface, base ± truncate to tapered, tip acute, margin doubly serrate except at base
Pistillate inflorescence 3–5 cm; bract fringed with hairs
Ecology: Streamsides, springs
Elevation: 600–2500 m.
Bioregional distribution: Klamath Ranges, High Cascade Range, High Sierra Nevada, Great Basin Floristic Province, Desert Mountains
Distribution outside California: scattered in w N.America
Flowering time: Apr–May
Horticultural information: WET: 1, 2, 3, 4, 5, 6, 7, 9, 10, 14, 15, 16, 17, &SHD: 18, 19, 20, 21, 22, 23, 24; STBL.