Structure of the cuniculus nectary in Brassavola flagellaris Barb. Rodr. (Laeliinae Benth., Orchidaceae)

To date, the structure of the cuniculus nectary has not been studied in detail. Furthermore, the secretory mechanism of such nectaries has not been investigated. The present paper describes, for the first time, the structural organization and ultrastructure of the cuniculus nectary in the moth-pollinated orchid Brassavola flagellaris Barb. Rodr. This tubular structure is situated between the perianth tube and ovary and, in its possession of thick, cellulose cell walls, resembles the nectary of ornithophilous taxa. The presence of large secretory vesicles that fuse with the plasmalemma indicate that granulocrine nectar secretion occurs in this species. The lumen of the cuniculus is lined with unicellular hairs. However, the cuticle overlying the whole epidermal surface lining the lumen (both glabrous and pubescent regions) was coated with nectar residues and became distended and cracked, indicating that this entire tissue is probably involved in nectar secretion.