A scrambling, annual, nitrogen-fixing climber, up to 1.2m high, with angular, winged stems, mid-green leaves divided into two narrowly elliptic, pointed leaflets, up to 15cm long and up to 1cm wide, and solitary flowers, up to 2.5cm across, usually sky-blue with a pink and white spot on the upper petal, sometimes pink or white, in late spring and early summer.