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Populus key for mature vegetative material
See list of 8 species in this subkey-
1a. Petioles broad-elliptic to terete in cross-section (sometimes slightly flattened near the apex), usually with a shallow channel on the upper surface
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2a. Mature leaf blades of long shoots abaxially tomentose, the margins varying from 3- to 5-lobed or irregularly serrate with coarse teeth
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2b. Mature leaf blades abaxially glabrous or with pubescence confined to the main veins, the margins regularly serrate or crenate-serrate
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3a. Leaf blades obtuse to rounded at the apex, cordate at the base [Fig. 885], sometimes narrowed to a short, broad base prior to junction with petiole, without orange resin on the abaxial surface, permanently pubescent on the abaxial veins; terminal winter bud not or scarcely viscid
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3b. Leaf blades acute to short-acuminate at the apex, broad-cuneate to subcordate at the base, often with streaks of orange resin on the abaxial surface, glabrous; terminal winter bud very viscid
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1b. Petioles conspicuously compressed from the lateral surfaces, without a channel on the upper surface
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4a. Leaf blades with a definite, though sometimes very narrow, translucent margin [Fig. 884]
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5a. Leaf blades on long shoots 5–10 cm long, eciliate, crenate-serrate with teeth ca. 1 mm tall; apex of petiole without glands; branchlets terete; lateral winter buds appressed
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5b. Leaf blades on long shoots 10–18 cm long, ciliate, serrate with teeth 2–5 mm tall; apex of petiole with 2–5 glands; branchlets often somewhat 4-angled; lateral winter buds ascending
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4b. Leaf blades lacking a translucent border [Fig. 886]
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6a. Leaf blades narrow-ovate to broad-ovate, (5–) 7–12 cm long; terminal winter buds pubescent
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6b. Leaf blades rhombic to suborbicular or reniform, 2–8 (–10) cm long; terminal winter buds glabrous to sparsely pubescent
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7a. Leaf blade regularly denticulate with 18–30 (–40) teeth per margin up to 1 mm tall [Fig. 886]
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7b. Leaf blade coarsely sinuate-dentate with mostly 5–10 teeth per margin taller than 1 mm
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Each photo represents one species in this subkey.