title: Floral elaiophores in Lockhartia Hook. (Orchidaceae: Oncidiinae): their distribution, diversity and anatomy.
abstract: OBJECTIVE
  A significant proportion of orchid species assigned to subtribe Oncidiinae produce floral oil as a food reward that attracts specialized bee pollinators. This oil is produced either by glabrous glands (epithelial elaiophores) or by tufts of secretory hairs (trichomal elaiophores). Although the structure of epithelial elaiophores in the Oncidiinae has been well documented, trichomal elaiophores are less common and have not received as much attention. Only trichomal elaiophores occur in the genus Lockhartia, and their distribution and structure are surveyed here for the first time.
  
  
  METHODS
  Flowers of 16 species of Lockhartia were studied. The location of floral elaiophores was determined histochemically and their anatomical organization and mode of oil secretion was investigated by means of light microscopy, scanning electron microscopy and transmission electron microscopy.
  
  
  CONCLUSIONS
  All species of Lockhartia investigated have trichomal elaiophores on the adaxial surface of the labellum. Histochemical tests revealed the presence of lipoidal substances within the labellar trichomes. However, the degree of oil production and the distribution of trichomes differed between the three major groups of species found within the genus. All trichomes were unicellular and, in some species, of two distinct sizes, the larger being either capitate or apically branched. The trichomal cuticle was lamellate, and often appeared distended due to the subcuticular accumulation of oil. The labellar trichomes of the three species examined using transmission electron microscopy contained dense, intensely staining cytoplasm with apically located vacuoles. Oil-laden secretory vesicles fused with the plasmalemma and discharged their contents. Oil eventually accumulated between the cell wall and cuticle of the trichome and contained electron-transparent profiles or droplets. This condition is considered unique to Lockhartia among those species of elaiophore-bearing Oncidiinae studied to date.
authors.affiliation: Escuela de Biología, Universidad de Costa Rica, Ciudad Universitaria Rodrigo Facio, Apdo. 11501-2060, San José, Costa Rica; and research associate, Jardín Botánico Lankester, Universidad de Costa Rica, Apdo. 1031-7050 Cartago, Costa Rica.
authors.forename: Mario A
authors.initials: MA
authors.lastname: Blanco
authors.forename: Kevin L
authors.initials: KL
authors.lastname: Davies
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Stpiczynska
authors.forename: Barbara S
authors.initials: BS
authors.lastname: Carlsward
authors.forename: Gretchen M
authors.initials: GM
authors.lastname: Ionta
authors.forename: Günter
authors.initials: G
authors.lastname: Gerlach
mesh_terms: D000818:Animals; D005075:Biological Evolution; D035264:Flowers / Q000502:physiology / Q000648:ultrastructure*; D029595:Orchidaceae / Q000502:physiology / Q000648:ultrastructure*; D010938:Plant Oils
chemical_list: D010938:Plant Oils
keywords: Anatomy; Lockhartia; Oncidiinae; Orchidaceae; callus; elaiophore; oil secretion; trichomes