Yellow oxalis (Oxalis corniculata) belongs in the the wood-sorrel flower family Oxalidaceae. Many of the plants in this family originate from tropical Brazil, Mexico and South Africa. The name false shamrock comes from the trefoil leaves, which closely resemble the leaves of clover. Other names include creeping lady's-sorrel, creeping oxalis, creeping wood-sorrel and procumbent yellow-sorrel. The example shown is a variety that has purple leaves. The stems of (Oxalis corniculata) can root from where they touch the ground, but, more usually, this plant grows as an annual. The main means of spreading is by seed, ejected forcibly from the ripe seed pods. Yellow oxalis can be a problem weed in some gardens and in lawns.