We conducted a vascular plant inventory of six National Park Service units in southwestern and south-central Alaska to establish baseline floristic information and identify species of conservation concern. Between 1998 and 2005, we collected 815 taxa, the majority of which were new records for one or more park units. We present descriptions of the rare taxa (Alaska Natural Heritage Program S1–S3 ranks) collected as part of the National Park Service inventories, as well as new collections that represent significant range extensions. Of the 45 taxa reported here, all but one are considered globally rare or rare within Alaska. Collections of six taxa, including the common species, represent range extensions of greater than 450 km, and collections of an additional 16 taxa were minor range extensions (> 150 km, < 450 km). We include brief synopses of the vouchers, including general notes on the biogeography and rarity of these taxa. These and previous collections support the demarcation of southwestern Alaska as an important zone of floristic convergence. The central Alaska Range also represents a unique assemblage of boreal and maritime-associated taxa.