Comparative Floral Development and Anatomy Reveal Distinct Origins of the Gynophore in Meso-Papilionoideae

The Meso-Papilionoideae clade comprises most papilionoid legumes and includes small clades with heterogeneous floral morphologies. Some species have a sessile ovary, while in others the gynoecium is elevated by a stalk called a stipe or gynophore. This study provides a qualitative and comparative morphological analysis of meso-papilionoid flowers, focusing on the anatomy, vascularization, and development of the ovary and gynophore. The objective is to unravel the ontogenic origin and anatomical nature of the gynophore in meso-papilionoid flowers. Floral buds at different developmental stages of seven meso-papilionoid species were examined using scanning electron microscopy and sectioned transversely and longitudinally for analysis under optical microscopy. The morphological variations in the examined flowers may represent evolutionary adaptations associated with their respective pollination syndromes. Ovary development follows a certain pattern among legumes, with limited variations, including the formation of a basal pedestal beneath the carpel suture in species bearing a gynophore. The gynophore is anatomically distinct from the ovary, exhibiting a stem-like nature, originating from the activity of an intercalary meristem on the basal pedestal of the ovary or receptacle. This qualitative anatomical approach represents a first step toward the homologation of gynophore types in Fabaceae, providing a basis for future quantitative and phylogenetic analyses.