Extrafloral nectaries in Passiflora pohlii Mast. (Passifloraceae): morpho-anatomical and ecological aspects of an understudied nectary morphotype in Passiflora L.

Abstract

Several species of Passiflora in the subgenus Decaloba bear yellow, circular glands that are between the major veins on the abaxial leaf surface, called ocelli, and commonly described as extrafloral nectaries (EFNs). Although poorly known anatomically, other studies have shown that for some Passiflora species these glands are ecologically important for playing a role in mutualistic relationships with ants. In this study, we determined the nectariferous nature and described the structure of ocelli in the leaves of Passiflora pohlii. We tested the exudates from ocelli for glucose and looked for fungi on the surface of the glands using scanning electron and confocal laser light microscopy. Ocelli of P. pohlii have an epidermis with multiple layers and secretory (or subsecretory) parenchyma. Two ant genera were found collecting profuse nectar from the glands. Fungal hyphae were found at the post-secretory phase. Altogether, these findings confirm that the ocelli of P. pohlii are extrafloral nectaries of ecological importance to the mutualistic interactions between visiting ants and these nectar-secreting structures.