Obtaining and selecting barley forms with valuable traits distinctive from the original genotypes is important from a scientific point of view, because the genetic diversity of crop plants represents the raw material for the development of varieties adapted to variable climatic conditions. As a result of research aimed at expanding the variability and diversity of spring barley, forms of barley with branched spike were obtained. The branched spike mutation was revealed in the offspring of somaclones (SC1), regenerated from immature embryos taken from donor plants (cv. Unirea, two-rowed spike), irradiated with gamma rays (100 Gy). Following the analysis of the offspring of plants with a branched spike in the SC2-SC3 generations, the instability of this mutation was highlighted, which was expressed with a frequency of 47.1% in the SC2 (2014) and wasn’t observed in the SC3 (2015). Subsequently, as a result of the evaluation over three years (2020-2022) of the same generation, we determined that this mutant trait was expressed phenotypically in 2020 (40-48%) and 2022 (26.19-30.28%), regardless of the generation and of spike morphology from which the grains were taken (branched or unbranched spike). As a result of estimating the frequency of the branched spike trait for 6 years, we assumed that this index varies depending on the climatic conditions, a fact also mentioned by other researchers, but without certain details. In order to establish the expression of this mutation, the database for the genes and genetic background of barley (NordGen) were detailly analyzed. Thus, we found that the branched architecture of the spike is determined by the recessive genes compositum (com2, com1), which determine the identity of the spike meristem and are involved in the thermoregulation of the morphology of the barley spike. In addition, these genes are expressed when seedlings are exposed to high temperatures (20-28 0C day and 15-23 0C night) starting from the initiation of inflorescence meristems to the spike morphogenesis stages. It was concluded that the mutation frequency increases simultaneously with the temperature during this vegetation period. This fact was confirmed following the evaluation of the temperature at the spike development stage of the mutant forms in different research years depending of the expression of mutation. Therefore, the scientific and practical importance