Least Hop Clover
(Trifolium dubium) 2013-5-18 Newark, DE
Found a large mat of irregular shape, maybe total 10 sq. ft., in Karen's neighbor's yard.
info:
http://www.florafinder.com/Species/Trifolium_dubium.php
Small flowerheads, 5-15 flowers on a head, are about 1/4". Leaves are toothed at the top and often the center leaf is notched at the top too. The stems are green to reddish-green and the whole plant doesn't grow much taller than a few inches.