Blackberries, members of the Rubus genus (often called brambles), are a globally popular fruit with a long history of cultivation and wild harvesting. They have been utilized by humans for thousands of years and are incredibly adaptable, thriving across temperate northern hemispheres and into South America. Understanding the number of varieties requires distinguishing between wild species and specific cultivars developed by modern breeding programs.
The Challenge of Counting Blackberry Varieties
A simple numerical answer to how many blackberry varieties exist is impossible due to the extreme complexity of Rubus taxonomy. The estimated number of wild blackberry species varies widely, ranging from about 250 to over 1,000 worldwide. This vast range stems from the plant’s unique reproductive biology, which includes frequent polyploidy (having more than two chromosome sets) and hybridization.
The greatest complication comes from apomixis, which is asexual reproduction through seed. Apomixis allows a plant to produce seeds that are genetically identical clones of the mother plant without pollination or fertilization. This mechanism results in the creation of countless “micro-species” or “agamospecies” in the wild, which are distinct, self-perpetuating clones. For example, the Rubus fruticosus aggregate in Europe alone is thought to contain over 2,000 such micro-species, making any definitive count arbitrary. The varieties consumers encounter in stores are specific, named cultivars developed through controlled breeding, not these wild micro-species.
Major Growth Habit Classifications
Despite taxonomic difficulties, blackberries are broadly categorized into three groups based on the physical structure of their biennial canes: erect, semi-erect, and trailing. This distinction is fundamental for growers as it determines the amount of physical support the plant requires. Individual canes live for two years, growing in the first year (primocane stage) and producing fruit in the second year (floricane stage) before dying back.
The erect varieties, such as ‘Navaho’ or ‘Ouachita’, produce stiff, self-supporting canes that stand upright without a trellis. These types are often the most cold-hardy and spread by producing new canes from root buds, forming a dense hedgerow. Trailing varieties, including dewberries and cultivars like ‘Marion’, have long, flexible canes that are not self-supporting. These plants must be trained onto a trellis or wire system to keep the fruit off the ground and facilitate harvesting.
The third category is semi-erect varieties, often hybrids between the other two types. These canes are vigorous but still require some support, typically a simple trellis, to manage high yields and prevent sprawling. Trailing varieties generally have the largest fruit and are common in the Pacific Northwest. The growth habit dictates the required planting distance and pruning strategy, making it a primary consideration for cultivation.
Key Traits Driving Commercial Selection
Modern breeding programs focus on developing new cultivars with traits desirable for commercial production and home gardening. Two significant distinctions are the presence of thorns and the timing of fruit production. The development of thornless varieties, such as ‘Chester Thornless’ or ‘Triple Crown’, revolutionized the industry by making harvesting significantly easier. Although thornless varieties first appeared in the 1920s, early versions often lacked flavor, a deficiency corrected by later breeding programs.
The second major advancement is the creation of primocane-fruiting varieties, which break the traditional biennial fruiting cycle. Most blackberries are floricane-fruiting, producing fruit only on second-year wood in the summer. Primocane-fruiting types, like the ‘Prime-Ark’ series, bear fruit on the tips of the first-year canes, typically in the late summer or fall. This allows growers to achieve a “double crop” in warmer climates or harvest a crop in northern regions where winter cold kills floricanes. Since their commercial release in 2004, this trait has become a major focus for breeders seeking to extend the harvest season and improve cold-weather reliability.