The marionberry is a cultivar of blackberry released in 1956 by the USDA Agricultural Research Service breeding program in cooperation with Oregon State University. It is named after Marion County, Oregon, where the berry was bred and tested extensively in the mid-20th century. it is the most widely planted trailing blackberry in the world. Oregon accounts for over 90% of the worldwide acreage of marionberries. Marionberries are an aggregate fruit formed in a cluster of many juice filled sacks called drupelets. The berry is glossy and, as with many blackberries, appears black on the plant, but turns a deep, dark purple when frozen and thawed.
Oregon produces 90% of the US grown, frozen blackberries found in US grocery stores, with Marion County and the Willamette Valley collectively accounting for most of that production.
Although related to a blackberry species considered to be a noxious weed the Himalaya blackberry (R. armeniacus) which is an aggressive invasive species They are commonly pruned and trained on trellises.
The berry was the inspiration for the West Coast League's Marion Berries collegiate summer baseball team, which was founded in 2024 and began to play in 2025.