Cleistogamy in barley is genetically determined by the presence of the recessive allele cly1, but the dominant allele at the linked locus Cly2 is epistatic over cly1. Although the molecular basis for cly1 action is well understood, that of Cly2 is not. Here we show that anther non-extrusion can occur not just when the lodicules fail to expand adequately (a trait which is fully determined by the allelic state at the cly1 locus), but by the premature timing of anthesis before the spike has emerged from the boot. The transcription of HvAP2 at cly1 is unaffected by the timing of anthesis. Where this occurs prematurely, by the time that the spike has emerged from the boot, the lodicules have already become shrunken and have lost the capacity to push the lemma and palea apart. Premature anthesis appears to be governed by a dominant gene, probably Cly2. Of the three phases of development of a non-cleistogamous barley floret (spike emergence from the boot, floret gaping induced by lodicule expansion and anther extrusion), genetic variation is available regarding at least the former two.