Rubus × 'Ark. 593' is an erect, thorny breeding selection developed by the University of Arkansas in 1970 that served as the foundational genetic bridge for all modern primocane-fruiting (fall-bearing) blackberries. It was generated from a 1967 cross between 'Brazos', an erect, highly productive tetraploid cultivar from Texas A&M University, and 'Hillquist', a wild, diploid Rubus argutus discovery from New York that possessed a rare, native ability to fruit on first-year canes. Because 'Brazos' was tetraploid (2n=4x) and 'Hillquist' was diploid (2n=2x), the cross normally would have yielded sterile triploid offspring; however, 'Ark. 593' arose from a rare unreduced male gamete from 'Hillquist', resulting in a fully fertile tetraploid selection (2n=4x).

The 'Ark. 593' selection itself did not physically express the fall-fruiting trait because primocane fruiting is governed by a recessive alleles, meaning the dominant, strictly summer-bearing (floricane) genetics of 'Brazos' completely masked the trait in the F1 generation. Instead, 'Ark. 593' was initially valued and utilized in breeding lines for its exceptionally early summer ripening window and upright growth habit. Its true genetic breakthrough was realized in the late 1980s when researchers at North Carolina State University self-pollinated 'Ark. 593' and successfully unmasked the recessive trait, recovering the first thorny, erect, primocane-fruiting tetraploid germplasm ('NC 194'). Structurally, 'Ark. 593' acts as a vital model in functional pomology, demonstrating how unreduced gametes can stabilize polyploidy while successfully introducing novel, complex survival traits from wild diploid germplasm into commercial culinary breeding populations.