Medicago lupulina is an annual or bi-annual plant, sometimes long-lived thanks to adventitious buds on the roots. The plant measures from 15 to 60 cm in height, with fine stems often lying flat at the beginning of growth and later erecting. The nodes bear three leaves, carried by a long petiole and have oval leaflets, partially toothed towards the tip. This species has very small yellow flowers are grouped in tight bunches. The fruit is a pod that does not open upon maturation, of a little arched form and bearing a single seed.