Flowers are reproductive shoots produced by determinate floral meristems. The role of FLORICAULA/ LEAPY-like genes in the specification of flowers varies between lineages and has not been characterized in a basal eudicot species. Here we report the phenotypic effects of virus-induced silencing of EcFLO, a FLORICAULA/LEAFY homologue in the California poppy Eschscholzia californica. EcFLO silencing resulted in repeated sepal and petal whorl formation and internodes between calyxes. A subset of silenced flowers showed reduced petal and stamen numbers and mosaic identities of floral organs. We also provide expression data of other floral regulator genes and conclude that EcFLO contributes to certain aspects of flower development, reflecting both functional conservation and differentiation among basal eudicots, core eudicots, and monocot grasses. EcFLO is involved in stamen and petal initiation, floral organ identity delimitation, suppression of internodes, and limitation of the number of perianth whorls. Further, silencing of EcFLO allows insights into perigynous flower development in Eschscholzia. We demonstrate that receptacle cup formation, by which the perianth and the androecium are elevated above the gynoecium late in flower development, responds to the initiation of the synsepalous calyx.