Appendicular origin and structure of the spur of Vochysiaceae flowers

Abstract

Floral nectaries are linked with animal pollinators and floral specialization, characterizing some plant groups, such as the mostly Neotropical Vochysiaceae. The phylogeny of these plants has been revised based on molecular data, but their conspicuous spurs were mostly neglected. The appendicular or receptacular origin of these spurs has been discussed but without ontogenetic or anatomical study, and the association between spur structure and pollination systems was never assessed. We studied the spurs of species of four genera of Cerrado Vochysiaceae (tribe Vochysieae), documenting their vascularization and comparing their structure to previously described pollination systems. The spur structure was roughly similar among species, and vascularization confirmed their appendicular origin. Subepidermic secretory tissue surrounded the lumen of the spur and nectar was secreted through nectarostomata. Besides differences in size and cuticle striation, no other association between spur structure and pollination system was observed. However, the structure is somewhat distinct in Qualea parviflora, which sports a pluriseriate internal epidermis padding the spur lumen, which may provide protection against damage by the large bees that visit these relatively small flowers. The conservative histology and vasculature somewhat confirmed the monophyly of the tribe Vochysieae and the appendicular origin of the spur in the Cerrado Vochysiaceae.