Please identify this ground cover
I live in central california and bermuda grass is a very common grass here so I planted it as a lawn. It was a very nice lawn until I planted two chineese elms in the center and they shaded out my lawn. A very interesting ground cover began to grown in this spot that looks like a clover or violet. Since I liked how nice it looked I decided to let it take over the this area since it does not grow very high and requires very little mowing . It also stays green all winter even n temperatures down in the 20's. Can someone tell me what it is? Thank you in advance for any info you can supply.