Storksbill. Erodium cicutarium.
Geraniaceae, the geranium family.

Plant: Low, hairy plant, 6"-12" high with dissected, fern-like leaves, and small clusters of pink, five-petalled flowers. Perennial.
Flowers: Pink, 1/2", with five petals and five sepals. Five fertile stamens form a central structure that somewhat resembles a tiny, inner flower surrounded by five sterile stamens. Flowers in small, umbel-like clusters with 3-10 blooms.
Leaves: Mostly basal, doubly pinnate, dissected into small lobed leaflets. Overall aspect is somewhat fernlike, the entire compound leaf to 6" of more in length.
Fruit: A five-parted, beak-like capsule.
Blooming: April-October
Habitat: Fields, roadsides, disturbed areas.

Comments: Introduced from Mediterranean Europe, the name derives from the beak-like fruiting capsule, a similarity shared with the native Cranesbill or wild geranium (Geranium maculatum), another member of the geranium family. The latter is a considerably larger, and more conspicuous plant with palmately-lobed leaves that blooms primarily in the spring.

Where to find it: Uncommon and sporadic in the park. I have found it along the eastern boundary with the medical campus.