Populus key for reproductive material

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  1a. Floral scales with margins dentate or with 3–7 narrow-triangular, long-ciliate lobes; staminate flowers with 5–12 (–15) stamens; carpellate flowers with 2 slender, bifid stigmas
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    P. alba

    2a. Floral scales merely dentate; capsules 3–5 mm long
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    2b. Floral scales with 3–7 narrow-triangular lobes; capsules 5–9 mm long
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      P. grandidentata

      3a. Branchlets (especially about the nodes) and terminal winter bud pubescent; stigmas lacking basal lobes; floral scales of staminate aments with 5–7 lobes; ovary pubescent
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      3b. Branchlets and terminal winter bud glabrous or nearly so; stigmas with recurved basal lobes; floral scales of staminate aments with 3–5 lobes (usually with more lobes 
in P. tremula); ovary glabrous (or sometimes scabridulous in P. tremula)
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        P. tremuloides

        4a. Mature capsules 5–9 mm long; scales of staminate aments with 3–5 lobes
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        P. tremula

        4b. Mature capsules usually shorter than 5 mm; scales of staminate aments usually with more than 5 apical lobes
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  1b. Floral scales with margins conspicuously fimbriate; staminate flowers with 12–80 stamens; carpellate flowers with 2–4 broadly dilated stigmas
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    P. heterophylla

    5a. Stigmas borne on elongate styles; staminate flowers with 12–20 stamens; anthers apiculate at the apex; capsules on pedicels 10–15 mm long; terminal winter bud not or scarcely viscid
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    5b. Stigmas sessile or nearly so; staminate flowers with (15–) 20–80 stamens; capsules on pedicels 2–10 mm long; anthers blunt or emarginate at the apex; terminal winter bud viscid
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      P. deltoides

      6a. Carpellate flowers with 3 or 4 stigmas; staminate flowers with (30–) 40–80 stamens; capsules 3- or 4-valved
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      6b. Carpellate flowers with 2 stigmas; staminate flowers with 20–30 stamens; capsules 2-valved
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        P. balsamifera

        7a. Ovules 15–22 per placenta; floral scales of carpellate flowers fimbriate with many, very narrow segments; stigmas spreading, with coarsely toothed, ± orbicular lobes; trees with spreading to ascending branches
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        P. nigra

        7b. Ovules 4–8 per placenta; floral scales of carpellate flowers fimbriate with 9–11 slender segments; stigmas reflexed and retrorsely appressed agaist the ovary, with entire, ± ovate lobes; trees often with strictly ascending branches producing a narrow, columnar form

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 Show photos of:   Each photo represents one species in this subkey.