The historic and extant spontaneous vascular flora of The New York Botanical Garden

The New York Botanical Garden occupies 100 hectares (250 acres) in the north central portion of Bronx County, New York. The property is a public garden with the majority of the grounds under cultivation. The Thain Family Forest, margins of the Bronx River, rock outcrops and areas of undeveloped landscape are important refugia for spontaneous plants, both native and non-native. We compiled data from historic lists of spontaneously occurring species, conducted original field work and searched the William and Lynda Steere Herbarium to determine the historic and extant spontaneous vascular plant flora of the Garden from 1899 to 2015. This is the first published inventory of the wild flora since 1899. The historic and extant flora comprises 695 species and infraspecies in 363 genera and 121 families. The extant flora comprises 429 species and infraspecies in 263 genera and 108 families. A total of 264 (62%) of the extant species and infraspecies are native and 165 (38%) are not native. All species are vouchered by herbarium specimens collected between 1881 and 2015. All herbarium vouchers are databased, imaged and available online. Forty-six species and infraspecies are new Bronx County records. Among the rare extant species and infraspecies on the New York State Department of Environmental Conservation Active Inventory List are three critically imperiled (S1) and two imperiled (S2) taxa, and Carex aggregata that was thought to be historical (SH, no existing sites known) in New York State, but was found in 2009 on the grounds. The number of extant rare species and infraspecies, the total number of extant taxa and the percentage of native verus non-native species strongly supports the conclusion that The New York Botanical Garden is an important and significant refugium or hotspot for local biodiversity.