Barley (Hordeum vulgare) double mutants Hv-Hd/tw2, formed by hybridization, are characterized by inherited phenotypic instability in the development of inflorescences and floral organs. Šiukšta et al. study callus cultures and intact plants and find that the auxin inhibitors HFCA and PCIB as well as 2,4-D partially rescue several different features of single and double mutants. The results suggest that ectopic auxin maxima or deficiencies arise in various regions of the inflorescence (spike)/flower primordia. Based on the phenotypic instability observed, definite trends in the development of ectopic flower structures can be outlined, from insignificant outgrowths on awns right through to flowers with sterile organs.