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Key to Rubus, Key D: American blackberries

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1 Canes armed primarily with bristles or slender-based prickles.
..2 Canes armed with slender-based prickles; leaves soft-pubescent beneath
..2 Canes armed with bristles as well as slender-based prickles; leaves thinly pubescent to glabrous beneath
1 Canes armed with heavy, stout-based, often recurved, prickles (or the canes essentially unarmed, the broad-based prickles few or almost absent).
....3 Leaflets oblanceolate to obovate, definitely wider beyond the middle, generally obtuse or rounded at the tip; leaves densely white- or gray-tomentose beneath; [primarily of the Coastal Plain]
....3 Leaflets lanceolate to ovate, widest below or near the middle, generally acute or acuminate at the tip; leaves glabrous to pubescent beneath, but the pubescence not notably tight and white or gray; [collectively widespread].
......4 Pubescence of the inflorescence rachis and pedicels predominantly gland-tipped, glandular hairs often present also on the young primocanes and the branches of the floricanes.
........5 Inflorescences racemose, flaring widely towards the tip, or leafy and < 2× as long as wide; calyx lobes > 7 mm long, > 3 mm wide.
..........6 Primocane leaves with central leaflets ovate to elliptic-oblong, usually about 2/3× as wide as long
..........6 Primocane leaves with central leaflets ovate to elliptic-oblong, usually about 3/4× as wide as long (or wider)
........5 Inflorescences narrowly racemose, usually appearing almost leafless (the bracts much smaller than the leaves, at least 2× as long as wide; sepals 5-7 (-8) mm long, 2.0-3.5 mm wide.
............ 7 Primocane leaves with terminal leaflets 1-1.4× as long as wide
............ 7 Primocane leaves with terminal leaflets < 1.6× as long as wide.
............ ..8 Canes unarmed or with a few, scattered short prickles
......4 Pubescence of the inflorescence rachis and pedicels nonglandular.
............ ....9 Primocane leaves with central leaflets ovate-elliptic to nearly orbicular; floricanes generally arching to low-arching, 5-13 (+) dm tall; inflorescences leafy-racemose.
............ ......10 Leaflet undersurfaces velvety-hairy
............ ......10 Leaflet undersurfaces glabrous to moderately soft-hairy.
............ ........11 Leaves glabrous (or very nearly so) beneath; canes with at most few and weak prickles; leaflets of the primocanes with attenuate to caudate apices
............ ........11 Leaves softly pubescent beneath; canes with many and strong prickles; leaflets of the primocanes with acute to acuminate apices
............ ....9 Primocane leaves with central leaflets narrowly elliptic, elliptic, or obovate; floricanes generally erect to arching, 7-40 dm tall; inflorescences various.
............ ..........12 Primocane leaves with central leaflets narrowly elliptic, > 2× as long as wide; inflorescences condensed at the ends of weak, leafy racemes or small, flaring clusters, the bracteal leaflets with jaggedly incised margins
............ ..........12 Primocane leaves with central leaflets elliptic to obovate, < 2× as long as wide; inflorescences with substantial flower stalks and bracteal leaflets with regularly toothed margins.
............ ............ 13 Primocane leaves with central leaflets generally widest above the midpoint; leaflet lower surfaces densely velvety, grayish-green; inflorescences with 5-11 flowers, often condensed at the ends of stout, well-armed racemes
............ ............ 13 Primocane leaves with central leaflets generally widest at or below the midpoint; leaflets softly pubescent beneath, but not grayish-green; inflorescences with 5-16 (-20) flowers, typically racemose (rarely short and flaring).
............ ............ ..14 Primocane leaves with central leaflets acuminate or strongly acuminate to a filiform tip; inflorescences narrowly racemose
............ ............ ..14 Primocane leaves with central leaflets acute to short-acuminate; inflorescences widened towards their apices
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