2.  Oxalis
A weed with pale green leaves divided into three heart-shaped leaflets invades thin areas of the lawn. The leaves are ¼ to ¾ inch wide and are similar to clover. The stems root at the lower joints and are often thinly covered with fine hairs. Small, bright yellow flowers are ½ inch long with five petals. Cucumber-shaped, light-green seed pods develop from the fading flowers. Plants may be 4 to 12 inches high with a prostrate-to-erect growth habit.