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1 Winter buds not viscid; stamens 5-20. |
2 Stamens 12-20; scales of the catkins deeply fimbriate; petioles terete; [section Leucoides] |
2 Stamens 5-12; scales of the catkins dentate or with only 3-7 linear- triangular lobes; petioles strongly flattened laterally (90 degrees to the plane of the leaf blade), especially near the junction with the blade; [section Populus]. |
3 Petioles strongly flattened laterally; leaves glabrous when mature ( pubescent when young in P. grandidentata); [native trees]. |
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4 Leaf margins finely crenulate- serrulate, with (12-) 15-35 (-45) teeth per side, the sinuses 0.5-1.0 mm deep; leaves glabrous; buds glossy brown |
3 Petioles terete or nearly so; leaves densely pubescent ( P. alba) or glabrescent ( P. ×canescens); [ exotic trees]. |
5 Leaves of vigorous shoots palmately 3-5 (-7)- lobed (and also toothed); leaves densely white- tomentose beneath when young and mature |
5 Leaves of vigorous shoots merely toothed; leaves glabrescent when mature |
1 Winter buds viscid (sticky and shiny as if recently varnished); stamens (15-) 20-80. |
6 Petiole terete or dorsally flattened (in the plane of the leaf blade), and often also channeled above; leaf blades dark green above, glaucous white beneath; leaf margin not translucent, finely serrate with teeth < 1 mm deep; [section Tacamahaca]. |
6 Petiole laterally flattened (90 degrees to the plane of the leaf blade), especially near the junction with the blade; leaf blades light green above, often paler beneath but not distinctly whitened; leaf margin translucent, finely to coarsely serrate with teeth > 1 mm deep. |
7 First-year branches reddish-brown; leaves noticeably paler beneath; flattened portion of petiole < 2× as deep as wide; early leaves with > 20 teeth per side, the largest < 2.5 mm deep; [probable intersectional hybrid of section Aegeiros and section Tacamahaca] |
7 First-year branches yellow- to orange- brown; leaves nearly the same color above and below; flattened portion of petiole > 2× as deep as wide; early leaves usually with < 20 teeth per side, the largest < 2.5 mm deep; [section Aegeiros]. |
8 Stigmas 3-4; stamens (30-) 40-80; [native tree, common] |
9 Glands at leaf blade base 3-6; leaf apices short- acuminate; fruiting pedicels grading from short at the base of the catkin to longer near the apex, 1-13 (-17) mm long; [widespread in our area] |
9 Glands at leaf blade base 2; leaf apices long- acuminate; fruiting pedicels relatively uniform in length, 1-6 (-8) mm long; [PA, OH, IN, IL, MO, OK, and TX and northwards and westwards] |
8 Stigmas 2-3; stamens (15-) 20-30; [ exotic trees, rare out of cultivation]. |
10 Floral disk 2-4 mm wide; stigmas 2-3; ovules and seeds 6-14 (-20) per placenta |
10 Floral disk 1-2 mm wide; stigmas 2; ovules and seeds 4-8 per placenta |