Flora of the Southeastern United States
2022 Edition

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Key to Rubus, Key D: American blackberries

1 Canes armed primarily with bristles or slender-based prickles.
..2 XXX
..2 YYY
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 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.
..........6 Primocane leaves with terminal leaflets < 1.6× as long as wide
..........6 Primocane leaves with terminal leaflets 1-1.4× as long as wide
........5 Inflorescences racemose, flaring widely towards the tip, or leafy and < 2× as long as wide; calyx lobes > 7 mm long, > 3 mm wide.
............ 7 Primocane leaves with central leaflets ovate to elliptic-oblong, usually about 2/3× as wide as long
............ 7 Primocane leaves with central leaflets ovate to elliptic-oblong, usually about 3/4× as wide as long
......4 Pubescence of the inflorescence rachis and pedicels nonglandular.
............ ..8 Primocane leaves with central leaflets ovate-elliptic to nearly orbicular; floricanes generally arching to low-arching, 5-13 (+) dm tall; inflorescences leafy-racemose.
............ ....9 Leaflet undersurfaces velvety-hairy
............ ....9 Leaflet undersurfaces glabrous to moderatelt soft-hairy.
............ ......10 Leaves glabrous (or very nearly so) beneath; canes with at most few and weak prickles; leaflets of the primocanes with attenuate to caudate apices
............ ......10 Leaves softly pubescent beneath; canes with many and strong prickles; leaflets of the primocanes with acute to acuminate apices
............ ..8 Primocane leaves with central leaflets narrowly elliptic, elliptic, or obovate; floricanes generally erect to arching, 7-40 dm tall; inflorescences various.
............ ........11 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
............ ........11 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.
............ ..........12 Primocane leaves with central leaflets generally widest above the midpoint; leaflet lower surfaces densely velety, grayish-green; inflorescences with 5-11 flowers, often condensed at the ends of stout, well-armed racemes
............ ..........12 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).
............ ............ 13 Primocane leaves with central leaflets acuminate or strongly acuminate to a filiform tip; inflorescences narrowly racemose
............ ............ 13 Primocane leaves with central leaflets acute to short-acuminate; inflorescences widened towards their apices