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Background    Passiflora  (passionflowers) makes an excellent model for studying plant evolutionary development. They are mostly perennial climbers that display axillary tendrils, which are believed to be modifications of the inflorescence. Passionflowers are also recognized by their unique flower features, such as the extra whorls of floral organs composed of corona filaments and membranes enclosing the nectary. Although some work on  Passiflora  organ ontogeny has been done, the developmental identity of both  Passiflora  tendrils and the corona is still controversial. Here, we combined ultrastructural analysis and expression patterns of the flower meristem and floral organ identity genes of the MADS-box  AP1 / FUL  clade to reveal a possible role for these genes in the generation of evolutionary novelties in  Passiflora .    Results  We followed the development of structures arising from the axillary meristem from juvenile to adult phase in  P. edulis . We further assessed the expression pattern of  P. edulis AP1 / FUL  homologues ( PeAP1  and  PeFUL ), by RT-qPCR and in situ hybridization in several tissues, correlating it with the developmental stages of  P. edulis .  PeAP1  is expressed only in the reproductive stage, and it is highly expressed in tendrils and in flower meristems from the onset of their development.  PeAP1  is also expressed in sepals, petals and in corona filaments, suggesting a novel role for  PeAP1  in floral organ diversification.  PeFUL  presented a broad expression pattern in both vegetative and reproductive tissues, and it is also expressed in fruits.    Conclusions  Our results provide new molecular insights into the morphological diversity in the genus  Passiflora . Here, we bring new evidence that tendrils are part of the  Passiflora  inflorescence. This points to the convergence of similar developmental processes involving the recruitment of genes related to flower identity in the origin of tendrils in different plant families. The data obtained also support the hypothesis that the corona filaments are likely  sui generis  floral organs. Additionally, we provide an indication that  PeFUL  acts as a coordinator of passionfruit development.    Electronic supplementary material  The online version of this article (doi:10.1186/s13227-017-0066-x) contains supplementary material, which is available to authorized users.

Expression patterns of Passiflora edulis APETALA1/FRUITFULL homologues shed light onto tendril and corona identities