Revisiting pericarp structure, dehiscence and seed dispersal in Galipeeae (Zanthoxyloideae, Rutaceae)

Rutaceae is a large family, particularly variable in fruits which have traditionally been used in the delimitation of infrafamilial taxa. Within the family, tribe Galipeeae stands out due to the high diversity of fruits with an exceptional complexity of structure and development, as well as various strategies of seed and fruit dispersal. To better understand the morphological evolution of the tribe, we selected distinct types of fruits occurring in Erythrochiton (subtribe Galipeinae) , Esenbeckia , Helietta and Metrodorea (subtribe Pilocarpinae) and comparatively analyzed their structure and development under light microscopy. Erythrochiton has a follicarium, Esenbeckia and Metrodorea capsules, and Helietta a samarium. All species investigated have multiplicative pericarp, resulting in large fruits containing many layers of fibers in the endocarp. The follicarium and capsules grow equally by diffuse cell divisions, but the samarium grows more markedly in the median dorsal part of mericarps, forming wings associated with an aerenchyma, which reduces their specific weight, facilitating dispersal by wind. The loculicidal capsules open along a dorsal dehiscence line, while the ventricidal follicles of the follicarium open along the ventral slit directed by the ventral vascular bundle. Both loculicidal capsules and follicaria dehisce explosively, and the seeds are ejected by the endocarp, which detaches from the pericarp. In addition to the novel observations in Galipeeae, a correlation between the degree of carpel union and the timing of schizocarpy is suggested for the first time.