Brian Mahieu demonstrating nocturnal hybridization techniques with H. citrina. Beginning in 1995 Mahieu focused his ambitious hybridizing program on this nocturnal species and up to half of his hybridizing was done at night. Subsequent generations of (H. citrina X cultivar) hybrids display extended blooming: most open for over 24 hours. The strictly nocturnal anthesis of H. citrina is recessive to the day-blooming (diurnal anthesis) habit.