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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  Rubus missouricus

2 Canes armed with bristles as well as slender-based prickles; leaves thinly pubescent to glabrous beneath  Rubus setosus

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]  Rubus cuneifolius

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  Rubus alumnus

6 Primocane leaves with central leaflets ovate to elliptic-oblong, usually about 3/4× as wide as long (or wider)  Rubus rosa

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  Rubus orarius

7 Primocane leaves with terminal leaflets < 1.6× as long as wide.

8 Canes well-armed  Rubus allegheniensis var. allegheniensis

8 Canes unarmed or with a few, scattered short prickles  Rubus allegheniensis var. gravesii

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  Rubus frondosus

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  Rubus canadensis

Show caption*© Scott Ward                      11 Leaves softly pubescent beneath; canes with many and strong prickles; leaflets of the primocanes with acute to acuminate apices  Rubus pensilvanicus

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  Rubus argutus

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  Rubus mollior

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  Rubus ablatus

14 Primocane leaves with central leaflets acute to short-acuminate; inflorescences widened towards their apices  Rubus laudatus