Yarrow,  Achillea millefolium
Asteraceae or Sunflower Family

Erect herb, 1-4 ft tall.  Leaves lance-shaped in outline, but intricately dissected.  Flower heads in an irregular, flat-topped cluster.  Each flower head has about a dozen dirty white ray flowers in a nearly spherical button surrounded by 4-6 white, sometimes pinkish, ray flowers, each notched at the end of the single petal.

A very common weed of roadsides and fields.  Occasionally cultivated as an ornamental; cultivated forms exist with deep pink or yellow ray flowers.  In Wildwood common in the butterfly meadows and along Wildwood Drive and the Riverway bike path.

Easily identified as there is nothing else quite like it in the park. At first glance it might be confused with Queen Anne's Lace (Daucus carota), but that has somewhat different leaves and very different flower clusters.