On affected plants, segregating in the progenies of tetraploid blackberries (Rubus fruticosus), flowers consisted of sepals, excessively divided petals and rudimentary anthers. Ovules on the receptacle were replaced by a whorl of tightly compressed, vegetative, bulbil-like structures. This resulted in sterile flowers but normal vegetative growth. Studies indicated that the abnormality was caused by a recessive gene which segregated or mutated to give plants homozygous recessive for this gene.