Format: ORAL

Malgorzata Stpiczynska1, Kevin L. Davies2, Emerson R. Pansarin3

1 Faculty of Biology, University of Warsaw, Botanic Garden, Al. Ujazdowskie 4, 00-478 Warszawa, Poland 2 School of Earth and Environmental Sciences, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, UK 3 Department of Biology, FFCLRP, University of São Paulo, Av. Bandeirantes 3900, Ribeirão Preto 14040-901, São Paulo, Brazil

In the flowers of Prosthechea Knowles Westc. (Laeliinae; Orchidaceae), there is an internal spur or reservoir formed by the fusion of the labellum base and the column. This structure acts as a nectary in nectar-secreting species. However, not all species in this genus produce nectar. In order to determine the structural adaptations for secretory activity or any constraints leading to the cessation of nectar production, the inner floral spur (cuniculus) of selected nectar-secreting and nectarless flowers was examined at the anatomical and cellular level. Our results indicate that the presence of nectar in the studied species is unrelated to the structure and character of the epidermis that covers inside of the spur, e.g. occurrence of the trichomes or papillae, and cuticle surface. Additionally, the ultrastructure of epidermal and subepidermal cells, distribution of plasmodesmata and the occurrence of reserve materials are similar in both types of flowers. Nectar, if present, becomes visible during the late bud stage, one day prior to flower opening, and is solely accessible during the first day of anthesis. It is then likely reabsorbed. Limited  amount of accessible nectar in the flowers of Prosthechea can represent a mechanism for pollinator manipulation, enabling plants to decrease the energetic costs of the interaction while still ensuring consistent pollinator visitation.