Alvars are globally rare ecosystems occurring mostly in the Great Lakes region of North America and the Baltic region of northern Europe. They are defined by calcareous rock (dolostone, limestone, or marble) plains with exposed pavement, thin soil with grasslands, or forested areas that are usually stunted. One of the largest alvars in the Great Lakes region is the Carden Alvar Natural Area (Carden), which is in southern Ontario ∼100 km NNE of Toronto and ∼25 km E of Orillia. In recent decades, recognition of the rare and uncommon species inhabiting Carden has led to the protection of 3035 of its ∼12,873 ha (24%). To continue to better understand Carden's wildlife, the first detailed survey of the lichens and allied fungi was completed in 2015 and is presented herein. The study was conducted on protected lands and revealed 199 species in 99 genera. Twenty-five species are provincially listed as S1 (critically imperiled), S2 (imperiled), or S3 (vulnerable) by the Ontario Natural Heritage Information Centre, several species represent major range extensions in the province, and a high number (17) of species with cyanobacteria as their primary photobiont were discovered. Results from this study can assist land managers in Carden to identify areas of high conservation value, develop sound conservation strategies, and justify the purchase or donation of additional property for conservation purposes.