Background: Leaves of Poaceae have a unique morphological feature: they consist of a proximal sheath and a distal blade separated by a ligular region. The sheath provides structural support and protects young developing leaves, whereas the main function of the blade is photosynthesis. The auricles allow the blade to tilt back for optimal photosynthesis and determine the angle of a leaf, whereas the ligule protects the stem from the entry of water, microorganisms, and pests. Liguleless variants have an upright leaf blade that wraps around the culm. Research on liguleless mutants of maize and other cereals has led to identification of genes that are involved in leaf patterning and differentiation. Results: We characterized an induced liguleless mutant (LM) of Aegilops tauschii Coss., a donor of genome D of bread wheat Triticum aestivum L. The liguleless phenotype of LM is under dominant monogenic control (Lg t ). To determine precise position of Lg t on the Ae. tauschii genetic map, highly saturated genetic maps were constructed containing 887 single-nucleotide polymorphism (SNP) markers derived via diversity arrays technology (DArT)seq. The Lg t gene was mapped to chromosome 5DS. Taking into account coordinates of the SNP markers, flanking Lg t , on the pseudomolecule 5D, a chromosomal region that contains this gene was determined, and a list of candidate genes was identified. Morphological features of the LM phenotype suggest that Lg t participates in the control of leaf development, mainly, in leaf proximal-distal patterning, and its dominant mutation causes abnormal ligular region but does not affect reproductive development. Conclusions: Here we report characterization of a liguleless Ae. tauschii mutant, whose phenotype is under control of a dominant mutation of Lg t . The dominant mode of inheritance of the liguleless trait in a Triticeae species is reported for the first time. The position of the Lg t locus on chromosome 5DS allowed us to identify a list of candidate genes. This list does not contain Ae. tauschii orthologs of any well-characterized cereal genes whose mutations cause liguleless phenotypes. Thus, the characterized Lg t mutant represents a new model for further investigation of plant leaf patterning and differentiation.