title: Flowers of the early-branching papilionoid legume Petaladenium urceoliferum display unique morphological and ontogenetic features.
abstract: OBJECTIVE
  Floral development can help to shed light on puzzling features across flowering plants. The enigmatic Amazonian monospecific genus Petaladenium of the legume family (Leguminosae) had rarely been collected and only recently became available for ontogenetic studies. The fimbriate-glandular wing petals of P. urceoliferum are unique among the more than 19000 legume species. Ontogenetic data illuminate the systematic position of the genus and foster our understanding on floral evolution during the early diversification of the papilionoid legumes.
  
  
  METHODS
  Flower buds were collected in the field, fixed in 70% ethanol, and investigated using scanning electron microscopy (SEM). Results were compared with existing material from early-diverging papilionoid legumes.
  
  
  RESULTS
  Formation of sepals and petals shows bidirectional tendencies. Stamens arise in two whorls, and the single carpel arises concomitantly with the outer stamen whorl. Gland formation starts early on the edges of the wing petals. The carpel reopens for a short time when the initiation of ovules is visible. Stomata at the base of the hypanthium indicate that the flower functions like other standard flag blossoms.
  
  
  CONCLUSIONS
  The floral ontogeny confirms the close affinity of P. urceoliferum with the florally heterogeneous, early-diverging papilionoid Amburaneae clade. The results strengthen the theory of a distinct experimental phase among early-branching papilionoid legumes during which a wider range of floral morphologies arose. Polysymmetry, monosymmetry, variable organ numbers, and a wide range of ontogenetic patterns laid the foundation for a successful canalization toward the more restricted but well-adapted dorsiventral papilionoid flag blossom.
authors.affiliation: Royal Botanic Gardens, Kew, Jodrell Laboratory, Richmond, Surrey, TW9 3DS, UK g.prenner@kew.org.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Prenner
authors.affiliation: Departamento de Botânica, Instituto de Biologia, Universidade Federal da Bahia, Rua Barão de Jeremoabo, s/n, Ondina 40170-115, Salvador, Bahia, Brazil Programa de Pós-Graduação em Botânica (PPGBot), Universidade Estadual de Feira de Santana, Av. Transnordestina, s/n, Novo Horizonte 44036-900, Feira de Santana, Bahia, Brazil.
authors.forename: Domingos
authors.initials: D
authors.lastname: Cardoso
authors.affiliation: Instituto Nacional de Pesquisas da Amazônia (INPA), Department of Biodiversity, Av. André Araújo, 2936, Petrópolis 69060-001, Manaus, Amazonas, Brazil.
authors.forename: Charles E
authors.initials: CE
authors.lastname: Zartman
authors.affiliation: Programa de Pós-Graduação em Botânica (PPGBot), Universidade Estadual de Feira de Santana, Av. Transnordestina, s/n, Novo Horizonte 44036-900, Feira de Santana, Bahia, Brazil.
authors.forename: Luciano P
authors.initials: LP
authors.lastname: de Queiroz
mesh_terms: D005075:Biological Evolution; D007887:Fabaceae / Q000033:anatomy & histology* / Q000235:genetics / Q000254:growth & development; D035264:Flowers / Q000033:anatomy & histology* / Q000235:genetics / Q000254:growth & development
keywords: Amburaneae clade; Leguminosae; Papilionoideae; Petaladenium urceoliferum; flag blossom; flower development; flower evolution