Natural Places to Observe Native Plants
These lists are of native plants of Philadelphia and the Delaware Valley. These plants have lived here for thousands if not millions of years. They are automatically suited to grow in this region. No worries about suitable zones, soil types or hardiness, their compatibility to the climate is built right in. Just match the moisture (moist or dry) and the light conditions (shade or sun) and you are good to go.
Common trees of PA (free, downloadable pdf)
Terrestrial and Palustrine Plant Communities of Pennsylvania (free, downloadable pdf)