We identify this as Rubus allegheniensis, but the various species of blackberries are numerous, and they hybridize, making identification a sloppy and uncertain business.
Blackberry canes are full of thorns, but they give us blackberries, so who are we to complain? The flowers that precede the berries are like little white roses, as befits a member of the rose family—but curiously wrinkled and untidy roses, as if they had slept in their petals after a long night of exhausting revelry. These blackberries were blooming in early May by a wooden fence in Scott Township.
Gray describes the genus and the species:
RUBUS [Tourn.] L. BRAMBLE. Calyx 5 (3-7)-parted, without bractlets. Petals 5, deciduous. Stamens numerous. Achenes usually many, collected on a spongy or succulent receptacle, becoming small drupes; styles nearly terminal. Perennial herbs, or somewhat shrubby plants, with white (rarely reddish) flowers, and usually edible fruit. (The Roman name, kindred with ruber, red.)
R. allegheniensis Porter. Shrubby, 1-2 m. tall; old canes purplish, armed with stout straightish prickles; leaflets appressed-villous above, velvety beneath; branchlets, pedicels (unarmed), etc., glandular-pubescent; flowers 2.5-3.5 cm. broad, racemose, only the lower leafy-bracted; petals narrowly obovate; fruit (rarely pale) generally subcylindric, of many rather small drupelets, of good flavor. (R. mllosus Man. ed. 6, in large part, not Ait.; R. nigrobaccus Bailey.) Dry open thickets and recent clearings, N. S. to Ont. and N. C., common.