plants.usda.gov/DocumentLibrary.../pdf/pg_viun.pdf
Cowpea is a warm-season, annual legume that exhibits a wide range of growth habits. Varieties may be short and bushy, prostrate, or tall and vine-like. Canopy heights can be 2–3 feet, depending on the variety. The upright stems are hollow and hairless, roughly 0.4 or 2/5 inch (1 cm) wide. The stems of twining varieties are thinner. The 4 inch (10 cm) long and 3 inch (8 cm) wide leaves are three-parted, egg-shaped, and hairless. The two lateral leaves are asymmetrical, and the terminal leaf is symmetrical. The plant also has extra floral nectaries, small pores on its leaves and stems of leaves that release nectar and attract beneficial insects.