There is a small three-leafed lawn weed spreading throughout the lawn. It forms a thick mat, grows about 2 inches tall, creeping along the ground. the leaves are pale green. It has currently gone to seed and the little seeds grow in a cluster of 10 or more typically. Each little seed has a few spikes on top. It grows very prolifically in the sunny part of the lawn, but has not invaded the area under trees yet. It is destroying the lawn. The plant is in the process of dying at this time. Does anyone know what this weed is and how to eradicate it. The soil is not good--very sandy despite being amended. Photo is attached. I would really appreciate any help anyone can give on this.