Fritillaria phitosia (Liliaceae) is described and illustrated from the lowlands of Mt. Tisseon, from Magnissia Peninsula, continental Greece (EC). It shows a unique combination of morphological features concerning the size, shape and colour of flowers and leaves, as well as a style divided up to its half. The new species belongs to F. sect. Fritillaria. It is related to F. euboeica and F. conica, both endemic of continental Greece, with also totally yellow or yellowish-green flowers, which have a style divided at least up to 1/3. Also it is related to the yellow-flowered F. carica, F. bithynica, F. forbesii, and F. sibthorpiana, occurring in the East Aegean Islands and in W Anatolia, as well as to F. pelinaea and F. rhodia, endemics to Chios and Rodos islands respectively, all with undivided styles (F. sect. Olostyleae). The new species is also compared to related Greek endemics F. sporadum, F. obliqua s.l., and F. ehrhartii, with dark purplish-brown flowers, at least externally. A key to the main morphological features of related yellow or yellowish-green flowered Fritillaria species occurring in Greece is given and their distribution map is presented. Additionally, the occurrence of yellow or yellowish-green individuals within Fritillaria species with purplish or dark-purplish flowers is reported. Finally, the karyotype and the conservation status of the new species are described, illustrated and discussed.