The morphological and genetic studies of the tlb mutant of common buckwheat Fagopyrum esculentum from the collection of the All-Russia Research Institute of Legumes and Groat Crops have demonstrated that gene TLB controls an important stage of flower development-it determines the lower boundary of simple perianths. The loss of TLB gene function leads to changes in the structure of the bract from scale-like to tepal-like. Gene TLB is assumed to limit, on the basal side, the region of the expression of genes determining the development of flower organs as petals.