2b. Section Arguti Rydb. (highbush blackberry)

Canes typically glabrous, erect to arching the first year, generally more clearly arched the second year; clonal by root-suckering, but rarely observed to tip-root. Prickles broad-based, straight or somewhat downward-curved. Primocane leaves mostly with 5 leaflets, sometimes with only 3 leaflets. Sepals never bearing gland-tipped hairs. Petals white. About 50 species, primarily in the eastern U.S. and adjacent Canada.

Alice et al. (in press) take a very different approach to this geographically and morphologically diverse section, treating most members as synonyms of a single, highly variable taxon, R. pensilvanicus Poir. Steyermark (1963) recognized four taxa within sect. Arguti. The treatment and descriptions of R. argutus and R. mollior herein resemble those of Steyermark. Steyermark’s other two taxa, R. ostryifolius Rydb. and R. pensilvanicus, are excluded. Davis et al. (1969) concluded that the combination of fragmentary type material along with Britton’s (1901) vague description makes it impossible to understand R. ostryifolius, and indicated that L. H. Bailey (1945) probably misinterpreted it in his treatment of sect. Arguti. Most collections that had been treated as R. ostryifolius are included here under R. ablatus and R. laudatus. Rubus pensilvanicus is native to the eastern United States and resembles its widespread congener, R. frondosus, but lacks that species’ broadly ovate central leaflets and its short, leafy inflorescences.