St. Lawrence Island, in the northern Bering Sea, is an important biogeographic link between the flora of northeastern Asia and northwestern North America. A vascular plant inventory was conducted on St. Lawrence Island in the 1960s by Steven Young in which 250 taxa were documented. Since that time, very few collections have been made on the island. We conducted a vascular plant survey to improve our understanding of baseline floristics and identify populations of species of conservation concern. Of the 166 taxa we collected in late July 2012, a number of collections represent new or significant finds. Eritrichium villosum, a Siberian taxon not previously recognized from North America, was collected on north-central St. Lawrence Island. This taxon, however, had been collected under a different name by Young in the late 1960s. Iris setosa subsp. setosa is a new record for the island. Iris setosa, although common along the eastern Bering Sea coast from Kotzebue Sound south through the Aleutians, appears to be very restricted on St. Lawrence Island and has only been noted by residents in recent years. Erigeron humilis and Moehringia lateriflora are also new records for the island. New populations were located of the globally rare species: Cardamine blaisdellii, Claytonia arctica, Micranthes nudicaulis subsp. nudicaulis, Papaver gorodkovii, Potentilla fragiformis, Ranunculus camissonis, and R. turneri subsp. turneri. We have included an annotated species list of 281 taxa, illustrated under-sampled regions of the island, and described the biogeographic affinities of the flora to other high latitude regions. The island's flora has strong biogeographic affinities to eastern Beringia (Alaska and western Yukon), particularly to the Seward Peninsula and less strongly to the Russian Far East. Numerous circumpolar arctic and alpine species were also present, with a minority of East-Asian species known from very few populations in extreme western Alaska.