Pollen ontogeny in Magnolia liliflora Desr

Pollen ontogeny contributes significantly to the evolutionary analysis and the understanding of the reproductive biology of seed plants. Although much research on basal angiosperms is being carried out there are still many important features about which little is known in these taxa, such as the sporophytic structures related to pollen development and morphology. In this study, pollen development of Magnolia liliflora was analyzed by optical microscopy and transmission electron microscopy. The aim of this paper was to supply data that will help characterize basal angiosperms. Microsporogenesis is of the successive type, so that tetrads are decussate or isobilateral. The callosic walls form by the centripetal growth of furrows. The secretory tapetum develops orbicules, which start to form in the microspore tetrad stage. Pollen grains are shed at the bicellular stage. The exine wall has a granular infratectum. Ultrastructural changes observed in the cytoplasm of microspores and tapetal cells are related to the development of the pollen grain wall and orbicules. Centrifugal cell plates are more usual for the successive type of microsporogenesis. The presence of the successive type of microsporogenesis with callosic walls formed by the centripetal growth of furrows could reflect the fact that the successive type in Magnoliaceae is derived from the simultaneous type. The granular infratectum of the ectexine and the presence of orbicules could indicate that this species is one of the most evolved of the genus.Fil: Galati, Beatriz Gloria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Recursos Naturales y Ambiente. Cátedra de Botánica Agrícola; ArgentinaFil: Zarlavsky, G. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Recursos Naturales y Ambiente. Cátedra de Botánica Agrícola; ArgentinaFil: Rosenfeldt, S.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; ArgentinaFil: Gotelli, Marina María. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Recursos Naturales y Ambiente. Cátedra de Botánica Agrícola; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Capitulum compartmentalization in Leucheria (Nassauvieae): Insights into the evolution of Asteraceae inflorescence

An unusual feature occurs in the capitula of Leucheria (Nassauvieae, Asteraceae), some phyllaries of the involucre are twisted and/or rotated. The different spatial orientations of these phyllaries, called here paleaceous phyllaries, divide the capitulum into compartments enclosing florets and fruits. Because the internal morphology of the phyllaries could play a role in the compartmentalization, the anatomy of the phyllaries together with their different spatial arrangements was analyzed in the 49 species of Leucheria. We found differences between the abaxial and adaxial epidermis, bulliform-like cells in the epidermis, and a callus at the base of the phyllaries. Cohesion, swelling, and turgor mechanisms in tissues are proposed to play a role in the positional changes of the phyllaries. The phyllaries bend, twist, rotate, and spread down and, excepting the latter, all are involved in capitula compartmentalization. The paleaceous phyllaries are already present in buds and continue during the whole plant life. Our results support previous phylogenetic hypotheses that suggest that Leucheria achieved a regular capitulum but maintained the remnants of an ancestor's pseudocephalium.Fil: Katinas, Liliana. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División de Plantas Vasculares; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Forte, Noelia Beatriz. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División de Plantas Vasculares; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentin

Paspalum schesslii (Poaceae, Paspaleae), a new species from Mato Grosso (Brazil) with an unusual base chromosome number.

Paspalum schesslii, a new species from the state of Mato Grosso in central-western Brazil, is described and illustrated. The new species is related to P. malmeanum, from central-western Brazil and eastern Bolivia, and Paspalum eucomum, from central Brazil. It comprises shorter plants with leaf blades and racemes shorter than those of the related species, and spikelets having obovate, deciduous upper florets. An unexpected chromosome number 2n = 12 was found in specimens of P. schesslii; thus it differs from both P. malmeanum, which has 2n = 20, and P. eucomum, for which 2n = 30 and 2n = 32 chromosome counts are here reported for the first time. The discovery of a new species having 2n = 12, which often cohabits with diploid populations of the widespread related species, P. stellatum, is consistent with an hypothesis about the hybrid origin of the polyploid cytotypes of P. stellatum having 2n = 32 and 2n = 52 chromosomes. Moreover, such an hybrid origin involving parental species with different base chromosome numbers (x = 6 and x = 10) could also explain the occurrence of 32 chromosomes in P. eucomum, potentially documenting a speciation mechanism that is otherwise unknown in the genus.Fil: Bonasora, Marisa Graciela. Universidad de Buenos Aires. Facultad de Agronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Pozzobon, Marisa T.. Ministerio da Agricultura Pecuaria e Abastecimento de Brasil. Empresa Brasileira de Pesquisa Agropecuaria; BrasilFil: Honfi, Ana Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Posadas | Universidad Nacional de Misiones. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Posadas; ArgentinaFil: Rua, Gabriel Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Agronomía; Argentin