Recently, we got to join Regina Alvarez, Daniel Atha, and Ken Chaya for one of their Central Park flora expeditions. For three years, the trio have been searching for wild — that is, not planted by the park — plants in Central Park.
Atha, who has travelled the world over collecting plants, uses an elegantly simple set-up for his plant press. Two boards, some newspaper sheets, and adjustable straps. The Waldo Tribune fits perfectly.
This is a Rosa: full identification would come later. 
The trio have doubled the number of known grass species in the park, found some very rare Pumpkin Ashes, and cataloged a lot of exotica. The links above will give you more details of their adventures in wild and perhaps not so wild sown plants that make Central Park their home.
For instance: Groundcherry (Physalis) or Tomatillo. In bloom in December. 
A 20 Point Guide for Defending Democracy. (So many points, four long years.)
And after this, Prospect Park! (please)