Gibberellins are required for dimorphic flower development in Viola philippica

•Photoperiod is a major determinant of CH–CL dimorphic flower development in Viola philippica.•GA biosynthesis is enhanced by photoperiod extension and high GA activity favors CL flower development in V. philippica.•High GAs repress the expression of B-class MADS-box genes in V. philippica.•The fine regulation of active GAs in response to photoperiod is crucial for CH–CL transition in V. philippica.