Morphology and anatomy of extrafloral nectaries in Solanum stramonifolium (Solanaceae)

Solanum stramonifolium Dunal. (Solanaceae) is a pioneer species very common in the Atlantic forest of northeast Brazil. The plants bear extrafloral nectaries (EFNs) that are frequently visited by ants. Ant exclusion experiments show reduced seed set in plants without ants. This paper describes the morphology and anatomy of the nectary of S. stramonifolium. This species bears structural EFNs, vascularized by both phloem and xylem. The nectary is located around the lower, external surface of the calyx, as a ring of five protuberances. Secretory cells are present only below these protuberances and arranged in several strata. The nectar is secreted by stomata situated on projections above the surface of these protuberances. Nectar secretion begins at the floral bud stage and continues through fruit development. We suggest that production of nectar during the entire reproductive period of S. stramonifolium functions as a mechanism of flower and seed protection.