Anatomical features related with pollination of Neottia ovata (L.) Bluff & Fingerh. (Orchidaceae)

The survey of anatomical features of Neottia ovata confirmed that the lip base and the groove function as a nectary. The secretory tissue was present in buds about 1,3 mm width. The sweet scent comes from the aromatic constituents of the nectar and also is released by the lip lobes and margins of all tepals. Additionally, the stomata present on the keels on the abaxial surface of sepals and large substomatal cavities may be connected with fragrance emission. The secretory function was not observed on the stem trichomes. The groove is formed by a single-layered epidermis, few layers of subepidermal cells and underlying parenchyma. The abundant starch grains present in buds, absent in sepals and lip epidermis in larger buds and almost absent in open flowers (visible in plastids in TEM) suggest gradual reduction during floral development and nectar secretion. The nectar was gathered under the cuticle, which was visible in the groove and lip base. The main mode of nectar release is by diffusion through micro-channels. The presence of irregular plasmalemma, dictyosomes, and profiles of ER could also indicate the granulocrine mode of secretion. The vesicles originated from ER or dictyosomes are fused with irregular plasmalemma. The irregular plasmalemma with invaginations (observed in groove) and cell wall protuberances (observed at the lip base) along the outer periclinal wall may function as highly specialized cells - transfer cells. Numerous idioblasts, visible in all tepals and in the staminodium, attract pollinators. In the anther, the endothecial cell thickenings were composed of numerous complete rings or helical segments in a closely spaced parallel arrangement (type I), providing the mechanical forces for anther dehiscence and opening and release of pollen grains.