Dollarweed is a perennial weed in Florida that grows well under wet conditions.
If you have seen it in your yard it probably means one of three things:
1. You are irrigating too much. Irrigating too often and irrigating too long can encourage dollarweed growth, try cutting back on your irrigation. Try not to irrigate within a couple of days of rain.
2. You have a leak in the irrigation system. In the picture above notice a hand at least 3 to 4 inches deep in water that is leaking from an irrigation pipe. This much water in one area is bound to cause landscape problems in addition to dollarweed (not to mention a high water bill!).
3. If it isn't an irrigation problem, then it may be due to rain. Consistent rain can encourage dollarweed, especially in depression areas in the yard (low areas where water collects after rain). This is still a good reason to cut back on irrigation!