Ilex opaca; Aquifoliaceae
According to the US Forest Service, American holly is “the hardiest known broadleaf evergreen”. Despite the cold tolerance, it’s a plant of the southeastern US, although it does grow along the Atlantic coast as far north as Massachusetts. And considering how popular it is in horticulture (over 1,000 known cultivars), it’s a little surprising that it’s listed as threatened in Pennsylvania and exploitably vulnerable in New York.
Sadly I have no pictures of the flowers, which are small, white, and inconsequential, or the berries.
More detailed information from the USFS here.