Black medic (Medicago lupulina) is considered an annual clover (but is not part of the clover genus). It has the teardrop-shaped leaves that are often found on clovers but, unlike other clovers, has yellow flowers. It is normally an annual, but in some warmer areas it can survive for several years before dying. Like many clovers, the leaves grow in groups of three and are oval shaped. Small pom-pom like yellow flowers will bloom off stems that grow off of the stem of each group of leaves.
Invasive in the Philippines, Hawaii, New Zealand and on a small number of islands in Oceania.