Stems erect, to 2 m, glabrous; armature of the stems of straight, spreading or slightly reflexed prickles 3-8 mm from a flattened base; petioles, flowering branches, and occasionally the pedicels and midveins commonly armed with smaller, distinctly hooked prickles; primocane lvs 5-foliolate, the terminal lfl long-stalked, commonly 8-12 cm, the intermediate pair conspicuously stalked and the lfls not overlapping; lfls all about alike in shape, oblong or oblong- oblanceolate, typically less than half as wide as long, sharply or often coarsely and irregularly serrate, widest above the middle, thence sharply acuminate to the tip, below the middle ±cuneate, with the sides usually conspicuously straight or straightish but serrate, acute to obtuse or rounded at base, softly pubescent beneath; pedicels villous, glandless or with a few scattered glands; fls in short, loose, open racemiform cymes. Chiefly a southern sp., from Md., Ky., and Mo. to Fla., and Tex., but n. occasionally to Mass. May, June. (R. blakei; R. fatuus; R. jugosus; R. louisianus)

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

©The New York Botanical Garden. All rights reserved. Used by permission.

From Flora of Indiana (1940) by Charles C. Deam

In Flora of North America, this taxon is part of a broadly defined Rubus pensilvanicus (Species link).  

Diagnostic Traits: central primocane leaflet narrowly elliptic (more than 2x longer than wide); inflorescence a leafy-raceme to small, flaring cluster.