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Betulaceae
See list of 5 genera in this familyReferences: Furlow and Mitchell (1990), Furlow (1997).
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1a. Leaf blades abaxially with black glands; mature stems with gray bark and slightly raised, longitudinal ridges; involucre a hastate-shaped, leaf-like bract; winter buds quadrangular in cross-section
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1b. Leaf blades without black glands (though resin or resin glands may be present); mature stems with smooth or exfoliating bark, variously colored (rarely uniformly gray), without longitudinal ridges; involucre a firm or woody scale, an enclosing husk, or an inflated, bladder-like bract; winter buds ± terete in cross-section
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2a. Involucre an inflated, bladder-like bract, the carpellate inflorescence resembling a hop-like cluster; mature stems with gray-brown bark that exfoliates in vertical strips; winter bud scales conspicuously longitudinally striate
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2b. Involucre a husk or a flat scale, the carpellate inflorescence resemling a cluster of fruits, an ament, or a cone; mature stems with variously colored bark, but this not exfoliating in vertical strips (though sometimes exfoliating and curling in horizontal strips or patches); winter bud scales not, or scarcely, longitudinally striate
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3a. Fruit a nut 10–15 mm long, enclosed in an husk-like involucre 15–70 mm long [Fig. 487]; staminate flowers without perianth; anthers pilose at the tip
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3b. Fruit a samara 1.2–4.5 mm long, subtended by, but not enclosed in, flat scales 2.5–13 mm long; staminate flowers with a minute calyx; anthers glabrous
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4a. Carpellate scales thin, decicuous with the fruit; androecium with 4 monothecal half-anthers; winter buds sessile; phyllotaxis ⅖
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4b. Carpellate scales thick, woody, long-persistent after the fruits are shed; androecium with 4 dithecal anthers; winter buds stalked (nearly sessile in A. viridis); phyllotaxis ⅓
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Each photo represents one genus in this family.