Habitat and ecology: Very common in old fields and edges of woodlands.
Occurence in the Chicago region: native
Etymology: Rubus is the Latin name for bramble and also means red. Allegheniensis means "from the Allegheny Mountains in the Eastern United States."
Author: The Morton Arboretum
From Flora of Indiana (1940) by Charles C. Deam
This is one of our most abundant highbush blackberries and is found more or less frequently probably throughout the state in almost all kinds of habitats but, like all the blackberries, it prefers open habitats. Bailey says, in comparison with [Rubus allegheniensis sensu stricto], that [Rubus impos] "lacks the narrow long-stalked leaflets, is less glandular, canes more terete and lacking the strong angles, broad-petaled flowers on very long slender pedicels (at least the lowest flowers in cluster) subtended by prominent outstanding bracts." Bailey refers specimens of mine from La Porte, Knox, and Posey Counties to this species. Not known from outside of Indiana.
Stems 0.5-2(-3) m, mostly erect or nearly so, the young primocanes often sparsely glandular; primocane lvs softly pubescent beneath; terminal lfl typically ovate-oblong, varying to ovate, 1-2 dm, widest near or below the middle, long-acuminate, finely and sharply serrate, rounded to truncate or subcordate at base; lateral lfls usually 4, smaller; armature of the stem of nearly straight prickles spreading at right angles or barely reflexed, much flattened at the long base; prickles of the petioles, pedicels, and midveins similar but prominently hooked; infl racemiform, commonly elongate and many-fld, the lower 1 or 2(3) fls subtended by lvs, the others by stipules only; pedicels tomentose and glandular; fls 2 cm wide; sep acute to more commonly short-caudate; pet cuneate and separate at base. Our commonest tall blackberry, occurring in a wide variety of mostly disturbed habitats, from N.S. and Que. to Minn., s. almost throughout our range and along the mts. to N.C. and Tenn. May-July. (R. abbrevians; R. alumnus; R. attractus; R. concameratus; R. flavinanus; R. frondisentis; R. inclinis; R. nuperus; R. ortivus; R. paulus; R. perinvisus; R. pugnax; R. reravus; R. saltuensis)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.