Osmophores as key players in pollination of Caladium bicolor (Araceae): a structural approach

All known species of the Caladieae tribe are beetle-pollinated, with floral volatiles linked to thermogenesis playing a key role in attracting pollinators. In Caladium bicolor, the inflorescences emit a strong scent that attracts nocturnal cyclocephaline beetles, though the exact site of scent emission remains debated. This study identified the osmophore and examined tissues and subcellular structures involved in scent production. Preliminary observations indicated the staminate portion of the spadix as the scent source. Microscopic analyses revealed that the secretory region is composed of papillary epidermis and underlying secretory parenchyma. Stomata exhibited signs of exudate release. Starch reserves in the parenchyma decreased during peak thermogenesis and constitute the energy source for this process. The distal portion of the synandria exhibited cells with cytoplasm rich in mitochondria, plastids, and other organelles. In addition to being fundamental in the process of thermogenesis, mitochondria, in association with plastids, plays a key role in the biosynthesis of some components of the floral bouquet, primarily terpenes. The cell structure, combined with active exudate production and pronounced thermogenesis in the fertile staminate portion, strongly supports its role as the primary site of floral fragrance emission.