Hairy vetch is a trailing or climbing, cool season biennial or annual legume. It has a shallow root system. Stems may grow 2 to 5 feet long. Leaves are terminated by branched tendrils. Leaves are composed of 10 to 20 leaflets. Leaflets are narrowly oblong to linearlanceolate. Stems and leaves of hairy vetch are usually pubescent (covered with soft woolly fuzz). Flowers are in clusters of 10 to 40. Each flower is violet and white to rose colored or white. Seed are round and black, developing inside elongated and flattened pods. This plant may become weedy or invasive in some regions or habitats and may displace desirable vegetation if not properly managed.
Taken from: http://plants.usda.gov/factsheet/pdf/fs_vivi.pdf