Rubus × 'Brewer' is a hybrid blackberry resulting from the cross between the 'Smooth Blackberry' (Rubus canadensis) and the 'Leafy-flowered Blackberry' (Rubus frondosus). This specific pairing was found as a chance seedling in 1920 and captures the distinctive cold hardiness and high altitude tolerance of R. canadensis, and combines it with the robust fruit production and upright habit of R. frondosus. While the R. canadensis parent contributes a refined, less aggressive growth pattern and smooth stems, the R. frondosus parent ensures a larger, more palatable fruit cluster that is well-suited for temperate climates.

The fruit of 'Brewer' is characterized by its deep black above-average sized berries and a flavor profile that balances the wild, earthy tartness of the mountain-dwelling R. canadensis with the sweet, fleshy drupelets typical of the more southern R. frondosus. While not on the market today, the 'Brewer' variety is significant example of early 20th-century pomology, representing an effort to domesticate the wild "brambles" of the eastern United States into reliable, high-quality garden crops.