Parsley dropwort (Oenanthe pimpinelloides), some people call it carrot weed Daucus carota, but it is a separate species. Parsley dropwort is a perennial (Carrot weed is an annual) that grows in Northland, Coromandel, Waikato and the East Coast invading and dominating pasture. It can do this because it has tubers on the roots which make it drought tolerant.
I visited Fraser who came to one of my workshops who had his dairy farm covered in this plant, but through soil and herbage testing he got the nutrients balanced in the soil and it is all but gone. Magnesium was the most lacking nutrient and parsley dropwort is the indicator.