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BETULACEAE BIRCH FAMILY

John O. Sawyer, Jr.

Shrub, tree; monoecious. Stem: trunk < 35 m; bark smooth to scaly, peeling in thin layers or not, lenticels present or not. Leaf: simple, alternate, petioled, deciduous; stipules deciduous; blade ovate to elliptic, generally serrate, generally ± doubly so. Inflorescence: catkin, generally appearing before leaves, often clustered; bracts each subtending 2–3 flowers, 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 or superior, chambers 2, each 1-ovuled by abortion, stigmas 2. Fruit: achene, nut, winged or not, subtended or enclosed by 1–2 bracts.
6 genera, 155 species: generally northern hemisphere; some cultivated. [Furlow 1997 FNANM 3:507–538] —Scientific Editor: Thomas J. Rosatti.

Key to Betulaceae

ALNUS ALDER
Stem: trunk < 35 m; bark smooth, gray to brown; twigs glabrous to fine-hairy, red-gray; lenticels small; winter buds stalked, 0–6-scaled. Leaf: glabrous to fine-hairy; blade 3–15 cm, cordate to elliptic or diamond-shaped. Staminate inflorescence: 5–20 cm; bracts each subtending 3 flowers, 4 bractlets. Pistillate inflorescence: 5–20 mm; bracts each subtending 2 flowers, 4 fused bractlets. Staminate flower: sepals 4; stamens 1–4. Pistillate flower: sepals 0. Fruit: many, in cone-like catkin, not enclosed by bract, winged, bracts 3 mm, woody, persistent.
± 25 species: northern hemisphere, South America. (Latin: alder) Root nodules contain nitrogen-fixing bacteria; wood used for interior finishing, to smoke fish, meats.

Key to Alnus

A. rubra Bong. RED ALDER
NATIVE
Tree. Stem: trunk < 25 m. Leaf: blade thick, base rounded to tapered, tip acute, margin tightly rolled under, adaxially gray-green, midrib, major veins indented, abaxially ± gray-green, rusty-hairy, or with rusty, sessile glands.
Wet places, especially after logging; < 1000 m. North Coast, w Klamath Ranges, Outer North Coast Ranges, Central Coast, San Francisco Bay Area; to southern Alaska, Idaho. Feb–Mar [Online Interchange]

Previous taxon: Alnus rhombifolia
Next taxon: Alnus viridis

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Citation for the whole project: Jepson Flora Project (eds.) 2013. Jepson eFlora, http://ucjeps.berkeley.edu/IJM.html, accessed on Apr 18 2014
Citation for this treatment: [Author of taxon treatment] 2012. Alnus, in Jepson Flora Project (eds.) Jepson eFlora, http://ucjeps.berkeley.edu/cgi-bin/get_IJM.pl?tid=12723, accessed on Apr 18 2014

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Bioregions in which Alnus rubra occurs Markers link to CCH specimen records. If the markers are obscured, reload the page [or change window size and reload]. Yellow markers indicate records that may provide evidence for eFlora range revision or may have georeferencing or identification issues.
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CCH collections by month

Duplicates counted once; synonyms included.
Species do not include records of infraspecific taxa.
Blue line denotes eFlora flowering time.