Depending on who you ask, blackberry plants are either an easy-to-care for variety of berry plant; a wild, low-growing shrub; or a noxious weed. Blackberries are common to most of the United States, but due to the characteristics they share with plants such as raspberries and blackcap (black raspberry) berries, some berry species are misidentified. Careful examination of berry plants will help you determine if they are true blackberries, and what variety of blackberry plant they may be.
Examine your plant closely. Blackberry, raspberry and blackcaps all grow as thorny shrubs. But blackberries are produced on canes that may be up to 10 feet in size and turn red with age. Blackberry leaves are woolly underneath, while raspberry varieties are not. The berries of a blackberry plant also mature in midsummer, while raspberry varieties mature in late summer.
Take photos of your specimen of plant for comparison. Select a digital camera with a macro setting that will allow you to take photographs at close range.
Compare your photos against a plant identification book that specializes in berries or native plants. Your local library may have such a book on its shelves, or may be able to borrow one through inter-library loan.
Check with your local land grant college to see if its horticulture or extension program has a focus on berries. Some universities, such as the University of Arkansas, have special programs focused on developing new varieties of blackberry plants for commercial use. Instructors at these universities may be able to identify your berry variety from the photograph you took.
Look through a phone book to see if there is a blackberry farm locally. A berry farm may have an employee on staff who is an expert in blackberries and can identify your plant.
Post your pictures to an online website such as USA Farmer. Frequent posters at these forums may be able to help you identify your plant.