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Key to Crataegus, Key C: hawthorns with leaf blades widest at midpoint or beyond midpoint; blade bases acute or cuneate;
leaves eglandular, or if glandular then twigs and branchlets not geniculate

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1 Leaves abaxially canescent, margins mostly entire; fruit calyx open, exposing pyrenes
1 Leaves abaxially pubescent, villous or glabrous, margins toothed; fruit calyx not fully open.
..2 Leaves spatulate or oblanceolate, < 13 mm wide; fruit < 6 mm diameter; pyrenes about 3 mm long
..2 Leaves variously shaped but most > 13 mm wide; fruit > 6 mm; pyrenes 4 mm long or more.
....3 Leaves abaxially with dense hair tufts in proximal main vein axils, especially in spring; [plants typically of wet or floodplain habitats].
......4 Inflorescence simple, 1-5-flowered; fruit 10-15 mm diameter, lustrous red, mature in late spring.
........5 Leaf blades mostly 5-7 cm long, elliptic, margin wavy or with uneven, blunt teeth
........5 Leaf blades usually < 5 cm long, most obovate, margin finely toothed.
..........6 Leaf adaxial surface usually glossy; whitish hair tufts in main vein axils abaxially
..........6 Leaf adaxial surface matte; reddish hair tufts in main vein axils abaxially
......4 Inflorescence compound, 5-20-flowered; fruit 5-15 mm diameter, dull red or orange-red, mature in autumn.
............ 7 Petiole 5-10 mm long; terminal shoot leaves < 25 mm broad
............ 7 Petiole > 10 mm long; terminal shoot leaves > 25 mm broad; [Virides series and hybrids].
............ ..8 Leaves glabrous, except for hair tufts.
............ ....9 Leaves mostly ovate; terminal shoot leaves suborbicular, unlobed or barely lobed; bases rounded
............ ....9 Leaves predominately lanceolate, elliptical, rhomboid or obovate; terminal shoot leaves often ovate; bases usually cuneate.
............ ......10 Leaves rarely lanceolate, mostly elliptical or rhomboid.
............ ........11 Leaf serrations small or crenate; terminal shoot leaves often incised on each side nearly to midrib
............ ..8 Leaves and/or inflorescences hairy, at least in spring.
............ ..........12 Terminal shoot leaves mostly ovate or rhomboid
............ ............ 13 Inflorescence villous; bracteoles firm, persist through anthesis; leaves coarsely toothed
............ ..........12 Terminal shoot leaves orbicular, elliptical or obovate
............ ............ ..14 Terminal leaves elliptical or obovate, prominently toothed; young leaves and inflorescence pubescent
....3 Leaves glabrous or with hairs scattered, not in tufts; [plants typically of upland habitats].
............ ............ ....15 Pyrenes channeled or pitted on inner sides.
............ ............ ......16 Leaves persistently pubescent, at least on petiole or main veins abaxially.
............ ............ ......16 Leaves glabrous or glabrate abaxially after maturity
............ ............ ............ ..20 Pyrenes with a shallow groove or depression; leaf venation vaguely reticulate, barely impressed adaxially
............ ............ ............ ..20 Pyrenes deeply grooved or pitted; leaf venation distinctly reticulate and impressed adaxially.
............ ............ ............ ....21 Stamens 15-20 per flower; anthers < 1 mm long.
............ ............ ............ ......22 Leaf blades often narrowly obovate or broadly elliptic; fruit 6-8 mm in diameter
............ ............ ............ ......22 Leaf blades broadly obovate, rhombic or suborbicular; fruit 7-12 mm in diameter
............ ............ ....15 Pyrenes plane on inner sides.
............ ............ ............ ........23 Sepals foliaceous, equaling or exceeding petal length in flower and persistent on fruit; flowers usually 1-5 per inflorescence.
............ ............ ............ ........23 Sepals not foliaceous, shorter than petals; flowers 5 or more per inflorescence
............ ............ ............ ............ 25 Thorns short (< 2 cm), or spinose spur shoots present; main lateral leaf veins run to sinuses and lobe tips in lobed leaves.
............ ............ ............ ............ ..26 Fruit black or blue; styles and pyrenes 3-5; most leaves elliptical; [native]
............ ............ ............ ............ ..26 Fruit red; styles and pyrenes 2; most leaves rhombic or obovate; [exotic]
............ ............ ............ ............ 25 Thorns usually > 2 cm long; main lateral leaf veins lead only to lobe tips in lobed leaves.
............ ............ ............ ............ ....27 Petioles distinctly glandular, usually with 3 or more glands persistent.
............ ............ ............ ............ ........29 Fruit flesh usually hard or dense; calyx collar elevated on fruit; leaves moderately lobed on terminal shoots.
............ ............ ............ ............ ........29 Fruit flesh dense or soft; calyx collar sessile or nearly so on fruit; leaves shallowly lobed or unlobed on terminal shoots.
............ ............ ............ ............ ............ ..32 Leaves conspicuously and persistently pubescent, petiolar glands stalked.
............ ............ ............ ............ ............ ........35 Leaves usually shallowly but sharply lobed; anthers purplish; [AL, GA, SC]
............ ............ ............ ............ ......28 Stamens usually 20 per flower (often 30 or more in C. triflora).
............ ............ ............ ............ ............ ..........36 Leaves pubescent, at least abaxially; anthers white or yellowish.
............ ............ ............ ............ ............ ............ ....39 Terminal shoot leaves 5-8 cm wide, with lobelike points; sepals patent in fruit
............ ............ ............ ............ ............ ............ ......40 Calyx collar often elevated on fruit; fruit flesh usually dense or dry; [Pulcherrimae series].
............ ............ ............ ............ ............ ............ ............ ..44 Petioles of smaller leaves winged 1/2 length; leaf lobes straight on inner/distal side.
............ ............ ............ ............ ....27 Petioles eglandular, or occasionally with 1 or 2 glands deciduous or obscure after spring. xx
............ ............ ............ ............ ............ ............ ............ ..........48 Stamens 10 per flower; leaf blades with 4-6 pairs of main lateral veins; calyx sessile on mature fruit
............ ............ ............ ............ ............ ............ ............ ..........48 Stamens 20 per flower; leaf blades with 3-4 pairs of main lateral veins; calyx collar often elevated on fruit.
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