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.

ALNUS

ALDER

Tree, shrub
Stem: trunk < 35 m; bark smooth, gray to brown; twigs glabrous to finely hairy, reddish gray; lenticels small; winter buds stalked, 2-scaled
Leaf glabrous to finely hairy; blade 3–15 cm, elliptic to ovate, base ± truncate to tapered, sometimes subcordate
Staminate inflorescence 5–20 cm; bracts each subtending 3 flowers and 4 bractlets
Pistillate inflorescence 5–20 mm; bracts each subtending 2 flowers and 4 fused bractlets
Staminate flower: sepals 4; stamens 1–4
Pistillate flower: sepals 0
Fruits many, in cone-like catkin, bracts 3 mm, woody, winged
Species in genus: 30 species: n hemisphere, South America
Etymology: (Latin: alder)
Reference: [Furlow 1979 Rhodora 81:1–121, 151–248]
Root nodules contain nitrogen-fixing bacteria; wood used for interior finishing, to smoke fish, meats.

Native

A. rubra Bong.

RED ALDER

Tree
Stem: trunk < 25 m
Leaf: blade thick, base tapered to round, tip acute, margin tightly rolled under, upper surface gray-green, midrib and major veins indented, lower surface ± gray-green, rusty-hairy, or with rusty, sessile glands
Ecology: Wet places, especially after logging
Elevation: 0–1000 m.
Bioregional distribution: North Coast, Outer North Coast Ranges, Central Coast, San Francisco Bay Area
Distribution outside California: to s Alaska, Idaho
Synonyms: A. oregona Nutt
Horticultural information: WET: 4, 5, 6, 7, 16, 17, 24 &SHD: 2, 3, 14, 15, 20, 21, 22, 23; STBL; timber.