Which perennial weed is known for its three leaflets and compact white flowers?

The perennial weed characterized by three leaflets and compact white flowers is indeed white clover. White clover typically features groups of three rounded leaflets, which are often marked with white or light green markings. This plant also produces small, dense clusters of white flowers, which can appear throughout the growing season.

In contrast, chickweed usually has a different leaf shape and does not produce flower clusters that resemble those of white clover. Ground ivy has a distinct, more rounded leaf and produces purple flowers rather than white ones, while prostrate spurge can be identified by its opposite leaf arrangement and does not have the three-leaflet structure typical of clover. Thus, the defining characteristics of white clover make it the accurate answer.