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Key to families | Table of families and genera

Specimen numbers are hyperlinked to records in the Consortium of California Herbaria data view where possible. Taxa are hyperlinked to entries in the Jepson Interchange via the "[Online Interchange]" link.


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

1. Tree, > 9 m, not forming thickets

2. Leaf blade adaxially shiny, base cordate to truncate ..... [A. cordata]

2' Leaf blade adaxially dull, base rounded to tapered

3. Leaf margin generally serrate, not tightly rolled under ..... A. rhombifolia

3' Leaf margin doubly serrate, tightly rolled under ..... A. rubra

1' Shrub, < 9 m, forming thickets

4. Lateral buds stalked, scales 0; pedicels < cone-like catkins; leaf thick, margin doubly serrate to crenate, teeth pointed, blunt, or rounded ..... A. incana subsp. tenuifolia

4' Lateral buds sessile, scales present; pedicels > cone-like catkins; leaf thin to firm, margin serrate, teeth pointed ..... A. viridis

5. Blade firm, adaxially dark green, margins generally densely serrate; coastal, 0–500 m ..... subsp. fruticosa

5' Blade thin, adaxially yellow-green, margins coarsely doubly serrate; montane, 1000–2700 m ..... subsp. sinuata


Citation for the whole project: Jepson Flora Project (eds.) [year] Jepson eFlora, [accessed on month, day, year]
Citation for an individual treatment: [Author of taxon treatment] [year]. [Taxon name] in Jepson Flora Project (eds.) Jepson eFlora, [URL for treatment]. Accessed on [month, day, year].
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