Floral development of the Ornithocephalus Glade (Oncidiinae, Orchidaceae): the origin of the tabula infrastigmatica, gynostemium appendices and labellar callus

The Ornithocephalus Glade comprises small epiphytes distributed in 12 genera and c. 120 species. Their flowers have complex structures, the homologies of which are difficult to interpret. Through ontogenetic studies, we identified the origins of the tabula infrastigmatica, floral appendages located in the gynostemium and the labellar callus. Using a scanning electron microscope (SEM), we analysed flowers at various developmental stages from representatives of three genera: Ornithocephalus (two species), Phymatidium (two species) and Zygostates (three species). The tabula infrastigmatica of Phymatidium results from the fusion of the lateral carpels and staminodes, with different degrees of synorganization across species and can be considered a plesiomorphic characteristic within the Glade. Contradicting hypotheses of a staminodial origin, the auricles present in this genus derive from the gynostemium. In Zygostates, the lateral appendices derive from staminodes and can show different development degrees, whereas in Ornithocephaus that character has been lost. We corroborate the view that the labellum is a single organ derived from the median petal and the labellar callus is derived from it.

Automated summary

The Ornithocephalus Glade consists of approximately 120 species in 12 genera, with complex flower structures that are difficult to interpret in terms of homologies. Through ontogenetic studies, the origins of certain key structures have been identified, shedding light on the evolutionary history of these plants.