title: Floral colleters in Pleurothallidinae (Epidendroideae: Orchidaceae).
abstract: OBJECTIVE
  The term colleter is applied to trichomes or emergences positioned close to developing vegetative and floral meristems that secrete a sticky, mucilaginous, and/or lipophilic exudate. Several ecological functions are attributed to these glands, but none are exclusive to colleters. Patterns of morphology and distribution of colleters may be valuable for systematics and phylogeny, especially concerning problematic and large groups such as the subtribe Pleurothallidinae, and are also essential to understand the evolution of these glands in Orchidaceae as a whole.
  
  
  METHODS
  We used scanning electron and light microscopy to examine the structure and occurrence of trichomes on bracts and sepals and in the invaginations of the external ovary wall (IEOW) in flowers in several developmental stages from species in seven genera.
  
  
  RESULTS
  The exudate was composed of polysaccharides, lipophilic, and phenolic compounds. Colleters were secretory only during the development of floral organs, except for the glands in the IEOW that were also active in flowers at anthesis. After the secretory phase, fungal hyphae were found penetrating senescent trichomes.
  
  
  CONCLUSIONS
  Trichome-like colleters seem to be a widespread character in Epidendroideae, and digitiform colleters are possibly the common type in this subfamily. Mucilage from IEOW colleters may aid in the establishment of symbiotic fungi necessary for seed germination. The presence of colleters in the IEOW may be a case of homeoheterotopy, in which extrafloral nectaries that produce simple sugar-based secretions (as in other orchid species) have changed to glands that produce secretions with complex polysaccharides, as in Pleurothallidinae.
authors.affiliation: Programa de Pós-Graduação em Biodiversidade Vegetal e Meio Ambiente, Instituto de Botânica, Av. Miguel Stefano 3687, Água Funda 04301-902, SP, Brazil.
authors.forename: Poliana
authors.initials: P
authors.lastname: Cardoso-Gustavson
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Campbell
authors.forename: Solange C
authors.initials: SC
authors.lastname: Mazzoni-Viveiros
authors.forename: Fábio
authors.initials: F
authors.lastname: de Barros
mesh_terms: D035264:Flowers / Q000033:anatomy & histology* / Q000254:growth & development / Q000502:physiology* / Q000648:ultrastructure; D018519:Meristem / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D029595:Orchidaceae / Q000033:anatomy & histology* / Q000254:growth & development / Q000502:physiology* / Q000648:ultrastructure; D062087:Plant Mucilage / Q000378:metabolism
chemical_list: D062087:Plant Mucilage
keywords: Epidendroideae; Oncidiinae; Orchidaceae; Pleurothallidinae; bracts; colleter; mucilage glands; orchids; ovary wall; sepals; trichomes