The flora of the Southwest Australian Floristic Region (SWAFR) is characterized by remarkable richness, endemism, spatial turnover and numbers of threatened taxa. Increasingly, evolutionary history is recognized as contributing to SWAFR biogeographical patterns, culminating in the theory of old, climatically buffered, infertile landscapes (OCBILs) [and their counterpoint: young, often disturbed, fertile landscapes (YODFELs)]. For the SWAFR, we: (1) developed a spatially explicit distribution of OCBILs and YODFELs; (2) analysed the spatial distribution of Threatened and Priority (Data Deficient) flora; and (3) tested the hypotheses that Threatened and Priority flora will be most strongly represented in OCBILs and will have small geographical ranges. We found that OCBILs and YODFELs dominated spatially distinct portions of the SWAFR. Threatened and Priority flora were not uniformly or randomly distributed and were more strongly characterized by narrow-range endemics than the non-Threatened flora. The occurrence of Threatened and Priority flora was positively correlated with the age of surface exposure of landscape features and unique geological features of limited extent (if not YODFELs). The concentration of Threatened flora in OCBILs provides the opportunity to improve conservation management through investigations of how plant traits favoured by evolution in OCBILs might increase or decrease the susceptibility of the flora to anthropogenic threats.