Looks like Oxalis corniculata--a weed (one of its common names is damn sorrel). I have seen this offered in tiny pots, cute but dangerous.
It's nearly impossible to eradicate. Truly one of the worst weeds I have. Only extreme diligence will end this beast.
This is another thread about this plant. But I think it is quite easy to eradicate, especially when indoors. The only problem is when you've got it with plants that are smaller and more delicate then Oxalis corniculata is. If you want to eradicate (I like the plant so I'm keeping it as "undergrowth" or "soilcover" below larger plants) just stop giving water and put it in the sun. It wil die out fairly quickly. But be carefull if you don't want it to spread around to other pots, because just before it dies it will flower and create seeds. Seeds will pop and jump a couple of feet away. To prevent that you could cut everything away with scissors. And just check daily for new flowers/starting seeds. If you've got it as a pest amongst another very delicate plant, then try getting your beloved plant out by repotting it to another fresh pot, taking along as little top soil as possible. If in the new pot accidentaly some seeds came along and start to grow just remove those seedlings. Outdoors though it can spread quite quickly and once it has spread it seeds once, they will keep popping up. But a week of hot weather should do. :) But the next rainshower will have it popping up everywhere again :). But replacing it with a tougher plant should do, I think.
