New Jersey has a surprisingly high concentration of native plant and animal species relative to other states.
Its native flora, comprised of more than 2,100 species, has representatives of more than 50% of the plant species found in the northeast from Pennsylvania to Maine despite the fact that it contains a mere 5% of the total land area of the region.
According to the 2000 U.S. Census, although it amounts to less than 0.26% of the total land area in the United States, and is the fourth smallest state in the nation, approximately 13% of the plant species in the U.S. can be found in New Jersey.
What allows for this high diversity? A variety of habitats and landscapes exist in New Jersey, from the mountainous Ridge and Valley in the north, to the Outer Coastal Plain in the south. Five such physiographic provinces can be found within the state, all within an hour’s drive of each other, and the unique combination of geological, topographical, and hydrological features that each of these represents has given rise to a wide range of environmental conditions within them, and a tremendous diversity in the state overall.
Source: NJDEP Office of Science
To learn more about the health and threats Endangered Plant Species Populations in New Jersey, you can download the state's report (49 pages, PDF)
Endangered Wildlife and Plants of the World
Vanishing Flora: Endangered Plants Around the World
Saving Endangered Plants and Animals (Science Solves It)