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Dennis W. Stevenson - One of the best experts on this subject based on the ideXlab platform.
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Complex reproductive secretions occur in all extant gymnosperm lineages: a proteomic survey of gymnosperm pollination drops
Plant Reproduction, 2019Co-Authors: Natalie Prior, Stefan A. Little, Ian Boyes, Patrick Griffith, Chad Husby, Cary Pirone-davies, Dennis W. Stevenson, P. Barry Tomlinson, Patrick AderkasAbstract:Key message Complex protein-containing reproductive secretions are a conserved trait amongst all extant gymnosperms; the pollination drops of most groups include carbohydrate-modifying enzymes and defence proteins. Abstract Pollination drops are aqueous secretions that receive pollen and transport it to the ovule interior in gymnosperms (Coniferales, Cycadales, Ginkgoales, Gnetales). Proteins are well established as components of pollination drops in conifers (Coniferales) and Ephedra spp. (Gnetales), but it is unknown whether proteins are also present in the pollination drops of cycads (Cycadales), Ginkgo (Ginkgoales), Gnetum (Gnetales), or in the pollination drops produced by sterile ovules occurring on pollen plants in the Gnetales. We used liquid chromatography–tandem mass spectrometry followed by database-derived protein identification to conduct proteomic surveys of pollination drops collected from: Ceratozamia hildae , Zamia furfuracea and Cycas rumphii (Cycadales); Ginkgo biloba (Ginkgoales); Gnetum gnemon and Welwitschia mirabilis , including pollination drops from both microsporangiate and ovulate plants (Gnetales). We identified proteins in all samples: C. hildae (61), Z. furfuracea (40), C. rumphii (9), G. biloba (57), G. gnemon ovulate (17) and sterile ovules from microsporangiate plants (25) and W. mirabilis fertile ovules (1) and sterile ovules from microsporangiate plants (138). Proteins involved in defence and carbohydrate modification occurred in the drops of most groups, indicating conserved functions for proteins in pollination drops. Our study demonstrates that all extant gymnosperm groups produce complex reproductive secretions containing proteins, an ancient trait that likely contributed to the evolutionary success of seed plants.
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Complex reproductive secretions occur in all extant gymnosperm lineages: a proteomic survey of gymnosperm pollination drops.
Plant Reproduction, 2018Co-Authors: Natalie Prior, Stefan A. Little, Ian Boyes, Patrick Griffith, Chad Husby, Cary Pirone-davies, Dennis W. Stevenson, P. Barry Tomlinson, Patrick Von AderkasAbstract:Complex protein-containing reproductive secretions are a conserved trait amongst all extant gymnosperms; the pollination drops of most groups include carbohydrate-modifying enzymes and defence proteins. Pollination drops are aqueous secretions that receive pollen and transport it to the ovule interior in gymnosperms (Coniferales, Cycadales, Ginkgoales, Gnetales). Proteins are well established as components of pollination drops in conifers (Coniferales) and Ephedra spp. (Gnetales), but it is unknown whether proteins are also present in the pollination drops of cycads (Cycadales), Ginkgo (Ginkgoales), Gnetum (Gnetales), or in the pollination drops produced by sterile ovules occurring on pollen plants in the Gnetales. We used liquid chromatography–tandem mass spectrometry followed by database-derived protein identification to conduct proteomic surveys of pollination drops collected from: Ceratozamia hildae, Zamia furfuracea and Cycas rumphii (Cycadales); Ginkgo biloba (Ginkgoales); Gnetum gnemon and Welwitschia mirabilis, including pollination drops from both microsporangiate and ovulate plants (Gnetales). We identified proteins in all samples: C. hildae (61), Z. furfuracea (40), C. rumphii (9), G. biloba (57), G. gnemon ovulate (17) and sterile ovules from microsporangiate plants (25) and W. mirabilis fertile ovules (1) and sterile ovules from microsporangiate plants (138). Proteins involved in defence and carbohydrate modification occurred in the drops of most groups, indicating conserved functions for proteins in pollination drops. Our study demonstrates that all extant gymnosperm groups produce complex reproductive secretions containing proteins, an ancient trait that likely contributed to the evolutionary success of seed plants.
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Phylogeny of the cycads based on multiple single-copy nuclear genes: congruence of concatenated parsimony, likelihood and species tree inference methods
Annals of botany, 2013Co-Authors: Dayana E. Salas-leiva, Dennis W. Stevenson, Michael Calonje, Alan W. Meerow, M. Patrick Griffith, Javier Francisco-ortega, Kyoko Nakamura, Carl E. Lewis, Sandra NamoffAbstract:†Background and aims Despite a recent new classification, a stable phylogeny for the cycads has been elusive, particularly regarding resolution of Bowenia, Stangeria and Dioon. In this study, five single-copy nuclear genes (SCNGs) are applied to the phylogeny of the order Cycadales. The specific aim is to evaluate several gene tree ‐ species tree reconciliation approaches for developing an accurate phylogeny of the order, to contrast them with concatenated parsimony analysis and to resolve the erstwhile problematic phylogenetic position of these three genera. †Methods DNA sequences of five SCNGs were obtained for 20 cycad species representing all ten genera of Cycadales. These were analysed with parsimony, maximum likelihood (ML) and three Bayesian methods of gene tree ‐species tree reconciliation, using Cycas as the outgroup. A calibrated date estimation was developed with Bayesian methods, and biogeographic analysis was also conducted. †Key Results Concatenated parsimony, ML and three species tree inference methods resolve exactly the same tree topology with high support at most nodes. Dioon and Bowenia are the first and second branches of Cycadales after Cycas, respectively, followed by an encephalartoid clade (Macrozamia ‐Lepidozamia‐Encephalartos), which is sister to a zamioid clade, of which Ceratozamia is the first branch, and in which Stangeria is sister to Microcycas and Zamia. †Conclusions A single, well-supported phylogenetic hypothesis of the generic relationships of the Cycadales is presented. However, massive extinction events inferred from the fossil record that eliminated broader ancestral distributions within Zamiaceae compromise accurate optimization of ancestral biogeographical areas for that hypothesis. While major lineages of Cycadales are ancient, crown ages of all modern genera are no older than 12 million years, supporting a recent hypothesis of mostly Miocene radiations. This phylogeny can contribute to an accurate infrafamilial classification of Zamiaceae.
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dna barcoding in the Cycadales testing the potential of proposed barcoding markers for species identification of cycads
PLOS ONE, 2007Co-Authors: Chodon Sass, Dennis W. Stevenson, Damon P Little, Chelsea D SpechtAbstract:Barcodes are short segments of DNA that can be used to uniquely identify an unknown specimen to species, particularly when diagnostic morphological features are absent. These sequences could offer a new forensic tool in plant and animal conservation—especially for endangered species such as members of the Cycadales. Ideally, barcodes could be used to positively identify illegally obtained material even in cases where diagnostic features have been purposefully removed or to release confiscated organisms into the proper breeding population. In order to be useful, a DNA barcode sequence must not only easily PCR amplify with universal or near-universal reaction conditions and primers, but also contain enough variation to generate unique identifiers at either the species or population levels. Chloroplast regions suggested by the Plant Working Group of the Consortium for the Barcode of Life (CBoL), and two alternatives, the chloroplast psbA-trnH intergenic spacer and the nuclear ribosomal internal transcribed spacer (nrITS), were tested for their utility in generating unique identifiers for members of the Cycadales. Ease of amplification and sequence generation with universal primers and reaction conditions was determined for each of the seven proposed markers. While none of the proposed markers provided unique identifiers for all species tested, nrITS showed the most promise in terms of variability, although sequencing difficulties remain a drawback. We suggest a workflow for DNA barcoding, including database generation and management, which will ultimately be necessary if we are to succeed in establishing a universal DNA barcode for plants.
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Cycads from the Triassic of Antarctica: Permineralized Cycad Leaves
International Journal of Plant Sciences, 2007Co-Authors: Elizabeth J. Hermsen, Edith L. Taylor, Thomas N. Taylor, Dennis W. StevensonAbstract:Permineralized cycad petioles and/or rachides with associated pinnae are described from two Triassic localities in the Queen Alexandria Range, central Transantarctic Mountains, Antarctica. Petiole‐rachides display an inverted‐omega‐shaped arrangement of vascular bundles typical of most genera of extant Cycadales and exarch primary xylem that link them to the modern order. Pinnae associated with the Antarctic petiole‐rachides are thin, with regularly spaced vascular bundles. They are similar to those of extant Zamia and most other genera of extant Cycadales, whose pinnae lack midribs. Other Mesozoic fossil cycads (e.g., Charmorgia, Lyssoxylon, Lioxylon) have endarch petiole vascular bundles that in some cases were previously considered more similar to those of Bennettitales than those of Cycadales. We suggest, however, that the endarch xylem of these taxa is typical of Cycadales because in extant cycads, the protoxylem changes from endarch to exarch within the base of the petiole. Evolution of cycad leaf f...
E. Mark Engleman - One of the best experts on this subject based on the ideXlab platform.
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Seed coat anatomy ofCeratozamia mexicana (Cycadales)
The Botanical Review, 2004Co-Authors: María Ydelia SÁnchez-tinoco, E. Mark EnglemanAbstract:La cubierta seminal le imparte protección a la semilla mediante una cutícula gruesa, células de taninos, mucílago, y una esclerotesta dura. La capa externa de la cubierta seminal es la sarcotesta; una cutícula gruesa cubre las paredes externas de las células epidérmicas. Esta epidermis presenta estomas y, en etapas tempranas, tricomas. Cuando la esclerotesta se endurece, los tricomas desaparecen. Las células subepidérmicas presentan drusas. En la sarcotesta los granos de almidón son abundantes desde junio hasta agosto, pero desaparecen durante la dispersión en septiembre. El parénquima se interrumpe por canales de mucílago forrados por células epiteliales. Las células de taninos se encuentran en la sarcotesta, esclerotesta, y paquicálaza. Diez sectores de una areola en la esclerotesta alrededor del micrópilo podrían corresponder a los apéndices del tegumento en algunas plantas fósiles, como Genomosperma kidstonii . The seed coat furnishes protection with a thick cuticle, tannin cells, mucilage, and a hard sclerotesta. The external layer of the seed coat is a sarcotesta; a thick cuticle covers the external walls of its epidermal cells. This epidermis bears stomates and, in the early stages, trichomes. The subepidermal cells have druses. Starch grains are abundant in the sarcotesta from June through August, but they disappear during dispersal in September. The parenchyma is interrupted by mucilage canals lined by epithelial cells. Tannin cells are found in the sarcotesta, sclerotesta, and pachychalaza. Ten sectors of an areole in the sclerotesta around the micropyle may correspond to the tips of the integumentary segments in some fossil plants, such as Genomosperma kidstonii .
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Seed Coat Anatomy of Ceratozamia mexicana (Cycadales)
The Botanical Review, 2004Co-Authors: María Ydelia Sánchez–tinoco, E. Mark EnglemanAbstract:The seed coat furnishes protection with a thick cuticle, tannin cells, mucilage, and a hard sclerotesta. The external layer of the seed coat is a sarcotesta; a thick cuticle covers the external walls of its epidermal cells. This epidermis bears stomates and, in the early stages, trichomes. The subepidermal cells have druses. Starch grains are abundant in the sarcotesta from June through August, but they disappear during dispersal in September. The parenchyma is interrupted by mucilage canals lined by epithelial cells. Tannin cells are found in the sarcotesta, sclerotesta, and pachychalaza. Ten sectors of an areole in the sclerotesta around the micropyle may correspond to the tips of the integumentary segments in some fossil plants, such asGenomosperma kidstonii.
Michael Calonje - One of the best experts on this subject based on the ideXlab platform.
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ZAMIA (ZAMIACEAE) PHENOLOGY IN A PHYLOGENETIC CONTEXT: DOES IN SITU REPRODUCTIVE TIMING CORRELATE WITH ANCESTRY?
Edinburgh Journal of Botany, 2016Co-Authors: J. A. R. Clugston, Michael Calonje, M. P. Griffith, G. J. Kenicer, C. E. Husby, D. W. Stevenson, D. P. LittleAbstract:The Cycadales are a group of significant global conservation concern and have the highest extinction risk of all seed plants. Understanding the synchronisation of reproductive phenology of Cycadales may be useful for conservation by enabling the targeting of pollen and seed collection from wild populations and identifying the window of fertilisation to aid in the cultivation of Cycadales. Phenological data for 11 species of Zamia were gathered from herbarium specimens. Four phenological characters were coded with monthly character states. DNA was isolated and sequenced for 26S, CAB, NEEDLY, matK and rbcL, and a simultaneous phylogenetic analysis of phenology and DNA sequence data was carried out. Three major clades were recovered: a Caribbean clade, a Central American clade and a South American clade. Eight species showed statistically significant synchronisation in microsporangiate and ovulate phenological phases, indicating the time of fertilisation. Close reproductive synchronisation was consistently observed throughout the Caribbean clade (statistically significant in four of five species) but was less consistent in the Central American clade (statistically significant in one of two species) and South American clade (statistically significant in three of four species). Ultimately, phenology is shown to be a potential driver of speciation in some clades of Zamia and in others to be a potential barrier to hybridisation.
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variability of vegetative flush colors in zamia Cycadales
2014Co-Authors: Claudia Calonje, Michael Calonje, Lindy Knowles, Chad HusbyAbstract:The color of new vegetative leaf flushes can vary among species of cycads. It is often used as a diagnostic character in taxonomy and is one of the most appreciated features of the group in ornamental horticulture. However, little is understood about the variability of flush color within species and wild populations. This paper discusses variability in flush color within the genus Zamia and uses a comprehensive ex situ conservation collection of three Zamia species (Z. angustifolia, Z. integrifolia, and Z. lucayana) collected from six islands in The Bahamas (Abaco, Andros, New Providence, Eleuthera, Grand Bahama, and Long Island) as a case study to examine this variability between species, between and within populations, and within progeny of individual mother plants. Flush color was found to be exclusively brown in Z. angustifolia and green in Z. lucayana. For Zamia integrifolia, flush color was exclusively green in seedlings derived from Abaco, Grand Bahama, and Eleuthera, but was variable in seedlings derived from Andros in New Providence, where both colors were present. On these two islands, flush color varied between and within populations, as well as within progeny of individual mother plants. The observed variability in flush colors suggests that a large number of in situ observations from multiple plants in several populations would be required to determine if a particular flush color character state is fixed and therefore useful as a diagnostic character. This can only be done through long term study of in situ populations, as leaf production is typically seasonal and is not necessarily synchronized or universal within wild populations. Therefore, we recommend against the use of flush color as a diagnostic character in cycad taxonomy.
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Phylogeny of the cycads based on multiple single-copy nuclear genes: congruence of concatenated parsimony, likelihood and species tree inference methods
Annals of botany, 2013Co-Authors: Dayana E. Salas-leiva, Dennis W. Stevenson, Michael Calonje, Alan W. Meerow, M. Patrick Griffith, Javier Francisco-ortega, Kyoko Nakamura, Carl E. Lewis, Sandra NamoffAbstract:†Background and aims Despite a recent new classification, a stable phylogeny for the cycads has been elusive, particularly regarding resolution of Bowenia, Stangeria and Dioon. In this study, five single-copy nuclear genes (SCNGs) are applied to the phylogeny of the order Cycadales. The specific aim is to evaluate several gene tree ‐ species tree reconciliation approaches for developing an accurate phylogeny of the order, to contrast them with concatenated parsimony analysis and to resolve the erstwhile problematic phylogenetic position of these three genera. †Methods DNA sequences of five SCNGs were obtained for 20 cycad species representing all ten genera of Cycadales. These were analysed with parsimony, maximum likelihood (ML) and three Bayesian methods of gene tree ‐species tree reconciliation, using Cycas as the outgroup. A calibrated date estimation was developed with Bayesian methods, and biogeographic analysis was also conducted. †Key Results Concatenated parsimony, ML and three species tree inference methods resolve exactly the same tree topology with high support at most nodes. Dioon and Bowenia are the first and second branches of Cycadales after Cycas, respectively, followed by an encephalartoid clade (Macrozamia ‐Lepidozamia‐Encephalartos), which is sister to a zamioid clade, of which Ceratozamia is the first branch, and in which Stangeria is sister to Microcycas and Zamia. †Conclusions A single, well-supported phylogenetic hypothesis of the generic relationships of the Cycadales is presented. However, massive extinction events inferred from the fossil record that eliminated broader ancestral distributions within Zamiaceae compromise accurate optimization of ancestral biogeographical areas for that hypothesis. While major lineages of Cycadales are ancient, crown ages of all modern genera are no older than 12 million years, supporting a recent hypothesis of mostly Miocene radiations. This phylogeny can contribute to an accurate infrafamilial classification of Zamiaceae.
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What is ZAMIA PRASINA (ZamiaCeae: Cycadales)?
Journal of the Botanical Research Institute of Texas, 2009Co-Authors: Michael Calonje, Jan MeermanAbstract:the name Zamia prasina is presently being applied in the horticultural industry and systematic literature to a little known taxon from the maya mountains in belize. an examination of the historical material of Zamia prasina, herbarium specimens, and wild Zamia popula tions in belize leads to the conclusion that the name does not correctly apply to this taxon but instead is a valid prior name for Zamia polymorpha that takes nomenclatural precedence. a lectotype for Z. prasina is designated. riority, b elize, Zamia prasina, Zamia polymorpha
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what is zamia prasina zamiaceae Cycadales
Journal of the Botanical Research Institute of Texas, 2009Co-Authors: Michael Calonje, Jan MeermanAbstract:the name Zamia prasina is presently being applied in the horticultural industry and systematic literature to a little known taxon from the maya mountains in belize. an examination of the historical material of Zamia prasina, herbarium specimens, and wild Zamia popula tions in belize leads to the conclusion that the name does not correctly apply to this taxon but instead is a valid prior name for Zamia polymorpha that takes nomenclatural precedence. a lectotype for Z. prasina is designated. riority, b elize, Zamia prasina, Zamia polymorpha
Natalie Prior - One of the best experts on this subject based on the ideXlab platform.
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Complex reproductive secretions occur in all extant gymnosperm lineages: a proteomic survey of gymnosperm pollination drops
Plant Reproduction, 2019Co-Authors: Natalie Prior, Stefan A. Little, Ian Boyes, Patrick Griffith, Chad Husby, Cary Pirone-davies, Dennis W. Stevenson, P. Barry Tomlinson, Patrick AderkasAbstract:Key message Complex protein-containing reproductive secretions are a conserved trait amongst all extant gymnosperms; the pollination drops of most groups include carbohydrate-modifying enzymes and defence proteins. Abstract Pollination drops are aqueous secretions that receive pollen and transport it to the ovule interior in gymnosperms (Coniferales, Cycadales, Ginkgoales, Gnetales). Proteins are well established as components of pollination drops in conifers (Coniferales) and Ephedra spp. (Gnetales), but it is unknown whether proteins are also present in the pollination drops of cycads (Cycadales), Ginkgo (Ginkgoales), Gnetum (Gnetales), or in the pollination drops produced by sterile ovules occurring on pollen plants in the Gnetales. We used liquid chromatography–tandem mass spectrometry followed by database-derived protein identification to conduct proteomic surveys of pollination drops collected from: Ceratozamia hildae , Zamia furfuracea and Cycas rumphii (Cycadales); Ginkgo biloba (Ginkgoales); Gnetum gnemon and Welwitschia mirabilis , including pollination drops from both microsporangiate and ovulate plants (Gnetales). We identified proteins in all samples: C. hildae (61), Z. furfuracea (40), C. rumphii (9), G. biloba (57), G. gnemon ovulate (17) and sterile ovules from microsporangiate plants (25) and W. mirabilis fertile ovules (1) and sterile ovules from microsporangiate plants (138). Proteins involved in defence and carbohydrate modification occurred in the drops of most groups, indicating conserved functions for proteins in pollination drops. Our study demonstrates that all extant gymnosperm groups produce complex reproductive secretions containing proteins, an ancient trait that likely contributed to the evolutionary success of seed plants.
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Complex reproductive secretions occur in all extant gymnosperm lineages: a proteomic survey of gymnosperm pollination drops.
Plant Reproduction, 2018Co-Authors: Natalie Prior, Stefan A. Little, Ian Boyes, Patrick Griffith, Chad Husby, Cary Pirone-davies, Dennis W. Stevenson, P. Barry Tomlinson, Patrick Von AderkasAbstract:Complex protein-containing reproductive secretions are a conserved trait amongst all extant gymnosperms; the pollination drops of most groups include carbohydrate-modifying enzymes and defence proteins. Pollination drops are aqueous secretions that receive pollen and transport it to the ovule interior in gymnosperms (Coniferales, Cycadales, Ginkgoales, Gnetales). Proteins are well established as components of pollination drops in conifers (Coniferales) and Ephedra spp. (Gnetales), but it is unknown whether proteins are also present in the pollination drops of cycads (Cycadales), Ginkgo (Ginkgoales), Gnetum (Gnetales), or in the pollination drops produced by sterile ovules occurring on pollen plants in the Gnetales. We used liquid chromatography–tandem mass spectrometry followed by database-derived protein identification to conduct proteomic surveys of pollination drops collected from: Ceratozamia hildae, Zamia furfuracea and Cycas rumphii (Cycadales); Ginkgo biloba (Ginkgoales); Gnetum gnemon and Welwitschia mirabilis, including pollination drops from both microsporangiate and ovulate plants (Gnetales). We identified proteins in all samples: C. hildae (61), Z. furfuracea (40), C. rumphii (9), G. biloba (57), G. gnemon ovulate (17) and sterile ovules from microsporangiate plants (25) and W. mirabilis fertile ovules (1) and sterile ovules from microsporangiate plants (138). Proteins involved in defence and carbohydrate modification occurred in the drops of most groups, indicating conserved functions for proteins in pollination drops. Our study demonstrates that all extant gymnosperm groups produce complex reproductive secretions containing proteins, an ancient trait that likely contributed to the evolutionary success of seed plants.
Analía E. Artabe - One of the best experts on this subject based on the ideXlab platform.
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a new cycad stem from the cretaceous in argentina and its phylogenetic relationships with other Cycadales
Botanical Journal of the Linnean Society, 2012Co-Authors: Leandro Carlos Alcides Martinez, Analía E. Artabe, Josefina BodnarAbstract:The cycads are an ancient group of seed plants. Fossil stems assigned to the Cycadales are, however, rare and few descriptions of them exist. Here, a new genus of cycad stem, Wintucycas gen. nov., is described on the basis of specimens found in the Allen Formation (Upper Cretaceous) at the Salitral Ojo de Agua locality, Rio Negro Province, Argentina. The most remarkable features of Wintucyas are: a columnar stem with persistent leaf bases, absence of cataphylls, a wide pith, medullary vascular bundles, mucilage canals and idioblasts; a polyxylic vascular cylinder; inverted xylem; and manoxylic wood. The new genus was included in a phylogenetic analysis and its relationships with fossil and extant genera of Cycadales were examined. In the resulting phylogenetic hypothesis, Wintucycas is circumscribed to subfamily Encephalartoideae, supporting the existence of a greater diversity of this group in South America during the Cretaceous. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170, 436–458.
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La Paleoflora Triásica del Cerro Cacheuta, Provincia de Mendoza, Argentina. Petriellales, Cycadales, Ginkgoales, Voltziales, Coniferales, Gnetales y Gimnospermas Incertae sedis
Ameghiniana, 2011Co-Authors: Eduardo Manuel Morel, Analía E. Artabe, Daniel Gustavo Ganuza, Adolfo ZúñigaAbstract:Abstract THE TRIASSIC PALEOFLORA OF CERRO CACHEUTA, MENDOZA PROVINCE, ARGENTINA. PETRIELLALES, Cycadales, GINKGOALES, VOLTZIALES, CONIFERALES, GNETALES INCERTAE SEDIS GYMNOSPERMS. Four stratigraphic logs were measured in detail at the Cacheuta hill (northwestern Mendoza Province, Argentina), and seven plantiferous levels were determined at Puesto Miguez and Agua de las Avispas. The main purpose of this paper is the systematic study of the paleoflora found in these secctions; the analized taxa belong to the Gymnospermopsida: Petriellales, Cycadales, Ginkgoales, Voltziales, Coniferales, Gnetales and Gymnospermophyta incertae sedis. The systematic study includes the following 25 identified taxa: Rochipteris truncata (Frenguelli) comb. nov., Nilssonia taeniopteroides Halle, Kurtziana brandmayri Frenguelli, K. cacheutensis (Kurtz) Frenguelli, Pseudoctenis falconeriana (Morris) Bonetti, P. spectabilis Harris, Baiera cuyana Frenguelli, B. rollerii Frenguelli, Ginkgoidium bifidum Frenguelli, Sphenobaiera argentin...
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Réplica al trabajo de Axsmith et al. (2007) publicado en Ameghiniana 44: 223-230: “The ‘New Approach to Corystospermales’ and the Antarctic Fossil Record: A Critique”
Ameghiniana, 2007Co-Authors: Analía E. Artabe, Mariana BreaAbstract:Resumen. En esta contribucion se da respuesta a la critica de Axsmith, Taylor y Taylor publicada en Ameghiniana 44: 223-230. En primer lugar, se insiste en no admitir como "evidencia inequivoca" de conexion organica a hojas de Dicroidiumodontopteroides con ramas con braquiblastos reportadas por Axsmith et al. (2000) en la localidad de Alfie, Antartida. Asimismo, el analisis del material de la Antartida realizado en el presente trabajo, permite interpretar que los organos cupulados de Umkomasiauniramia deberian asignarse a otro morfogenero probablemente peltaspermoide. Remarcamos que en la contribucion de Artabe y Brea publicada en Alcheringa se analizaron todos los caracteres que presentan los lenos de corystospermas de la Argentina y no se ignoraron los registros de la Antartida, ni las evidencias que dicho material aporta al entendimiento de las corystospermas. Asimismo, el trabajo de Axsmith et al., ya mencionado, abrio la discusion respecto del concepto de Corystospermales, las reconstrucciones utilizadas en los estudios filogeneticos y los caracteres vegetativos seleccionados para realizar analisis cladisticos. El estudio de los tallos de corystospermas de la Argentina, permite visualizar el sesgo que presentan los analisis cladisticos respecto de la utilizacion de caracteres vegetativos discriminantes en Medullosales, Cycadales y Corystospermales. Como ocurre con las Medullosales y las Cycadales, las Corystospermales deberian incluir dos taxones terminales correspondientes a las reconstrucciones propuestas para la Antartida y la Argentina. Abstract. REPLYTO AXSMITH ETAL. ´S (2007) PAPER PUBLISHED IN AMEGHINIANA 44: 223-230: “THE ´NEW APPROACH TO CORYSTOSPERMALES´ AND THE ANTARCTIC FOSSIL RECORD: ACRITIQUE”.This contribution replies to the critique of Axsmith, Taylor and Taylor published in the previous number of Ameghiniana. In first place, it is insisted on not admitting ‘as unequivocal evidence’ the supposed attachment of Dicroidium odontopteroides leaf to the axis with short shoots reported by Axsmith et al. (2000) at Alfie locality, Antarctica. Furthermore, the present analysis of cupulate organs, described at same locality by Axsmith et al. (2000), suggests that Umkomasiauniramia belongs to another morphotaxon with peltasperm affinities. It is remarked that in Artabe and Brea’s contribution published in Alcheringa all the characters present in Argentinean corystosperm stems were analyzed and not one record from Antarctica was ignored nor the evidence that the material provides to the understanding of the corystosperms. In addition, above mentioned Axsmith et al. ’s paper, has opened the discussion regarding to the Corystospermales concept, the reconstructions used in phylogenetic approaches and the vegetative characters selected in cladistic analysis. The study of Argentinean corystosperm stems allows visualizing the biased use -in cladistics- of discriminative vegetative characters in Medullosales, Cycadales and Corystospermales. As it happens with Medullosales and Cycadales, Corystospermales should include two end members corresponding to the reconstructions proposed for Antarctica and Argentina.
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Fossil Cycadales of Argentina
The Botanical Review, 1999Co-Authors: Analía E. Artabe, Dennis Wm. StevensonAbstract:A survey of Cycadalean taxa of Argentina (including Antarctica) is presented. The record of leaves represented by Nilssonia, Pseudoctenis, Ctenis, Mesodescolea, Ticoa, Almargemia , Kurtziana , and Zamia genera are summarized. Recent investigations made of cuticles with transmission and scanning electron microscopy are included. In stems, a preliminary study of two forms found in the Upper Cretaceous of Rio Negro Province are incorporated into Michelilloa, Bororoa , and Menucoa . The fossil record shows some characters of leaf morphology, presence of inverse xylem and medullary bundles, two kinds of leaf traces, and monoxylic and polyxylic steles of systematic importance when compared with both extant and fossil cycads. Affinities of fossil taxa related to extant families are suggested through analysis of the above-mentioned characters. The presence of medullary vascular rings related to the emission of terminal reproductive strobili are recognized in Bororoa and Menucoa . This character associated with polyxyly makes it possible to assign these genera to the Zamiaceae-Encephalartoideae sensu Stevenson, widening the paleogeographical distribution of this subfamily.
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Sistemática y paleoecología de la flora triásica de Hilario-Agua de los Pajaritos (formación El Alcázar) provincia de San Juan, Argentina
Ameghiniana, 1998Co-Authors: Daniel Gustavo Ganuza, Analía E. Artabe, Alba Berta Zamuner, Luis A. SpallettiAbstract:The systematic and paIaeoecological study of the Triassic taphoflora found in El Alcazar Formation (San Juan Province) is presented. This flora is represented by Sphenophyta, Filicopsida and Gymnospermopsida corresponding to Caytoniales, Cycadales, Ginkgoales and Coniferales groups. The following taxa are determined, described and compared: Neocalamites carrerei (Zeiller) Halle, Cladophlebis mesozoica Kurtz ex Frenguelli, C. mendozaensis (Geinitz) Frenguelli, Tranquiloxylon sp. A, Pachydermophyllum praecordillerae (Frenguelli) RetaIlack, Kurtziana cacheutensis (Kurtz) Frenguelli, Yabeiella mareyesiaca (Geinitz) Oishi, Sphenobaiera robusta (Arber) Florin, Heidiphyllum elongatum (Morris) RetaIlack y Linguifolium arctum Menendez, which indicates a late Mesotriassic age. Furthermore, botanical affinity to Cycadales of Yabeiella, previously regarded as a gymnosperm incertae sedis, is proposed. Three different paIaeocommunities are reconstructed from the fossiliferous bed.
