52 research outputs found

    The Fossil Record of Basal Monocots

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    The fossil record of basal monocots (Acorales and Alismatales) extends back to the Cretaceous in the Northern Hemisphere. While many fossils were originally assigned to these basal groups, rigorous paleobotanical studies show many of them to be misidentified. Acarus fossils have been reliably reported from the Eocene while those of Alismatales extend back to the early Cretaceous. The fossil record of basal monocots is usually represented by leaves, fruits, and seeds; however, some localities preserve stems with attached leaves and roots and even whole plants. A detailed examination of leaf venation patterns in alismatids has recently allowed the description of a new taxon from the Upper Cretaceous of Alberta based on leaves attributed to Limnocharitaceae. Anatomically preserved alismatid petioles (Heleophyton helobiaeoides) and well-preserved flowers/fruits are known from the Middle Eocene Princeton chert of British Columbia. A complete developmental sequence from flower to fruit is known, and this material has good possibilities for whole plant reconstruction. The extinct floating aquatic Limnobiophyllum (Araceae/Lemnoideae) and the genus Pistia have been the subject of morphological cladistic analyses and competing hypotheses of relationships among aroids and duckweeds. The fossil record and recent molecular studies support separate origins of Pistia and the duckweeds from within Araceae. The fossil taxon Pistia corrugata has been reexamined in light of new evidence and indicates the presence of a new genus that shows leaf morphology unlike that seen in extant Pistia, but with a similar growth habit. Fossil evidence indicates that the floating aquatic habit probably arose at least three times within Araceae

    Cuticular Features and Epidermal Patterns in the Genus Araucaria de Jussieu

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    This is the publisher's version, also available electronically from http://www.jstor.org.The cuticular organization and epidermal features of le aves from the four sections of the genus Araucaria, growing under similar environmental conditions, were studied by scanning electron microscopy. Cuticles from these extant species and the Jurassic fossil Araucarites santaecrucis were compared by rubber replicas and examination of the fossil leaf surfaces. Two distinct groups of araucarian leaves are distinguished by cuticular features. The Columbea-Bunya species have regular stomatal rows with polar cells always oriented in the same direction, four to five subsidiary cells, and a granular inner cuticle surface on both epidermal and subsidiary cells. The Eutacta-Intermedia species have four to seven subsidiary cells with thin cuticular flanges between guard cells and subsidiary cells, a smooth inner cuticular surface on both epidermal and subsidiary cells, and thinner intercellular flanges on epidermal cell walls. Epidermal features of a raucarian leaves appear to be taxonomically useful at the section level

    Studies of Paleozoic Seed Ferns: Additional Studies of Microspermopteris aphyllum Baxter

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    This is the publisher's version, also available electronically from http://www.jstor.org.The genus Microspermopteris is characterized as a small lyginopterid pteridosperm with a pentarch protostele, irregular cortical ridges, and multicellular trichomes. We describe the frond architecture and variability among axillary branches previously unknown for the genus. Fronds are small and delicate, exhibiting three orders of branching. Clasping V-shaped petioles produce primary pinnae alternately to suboppositely from adaxial projections. Primary pinnae in turn produce secondaries that bear two-, three-, or four-lobed ultimate laminar pinnules. Pinnules reconstructed from serial sections are morphologically similar to Sphenopteris-like compressions; however, the overall frond is reduced in size and complexity. While some axillary branches produce secondary xylem, others are composed entirely of primary tissues. Some axillary branches produce scalelike leaves in a tight helix; distally, immature buds are surrounded by flattened bud scales. Although Microspermopteris shows similarities to Heterangium in stelar and cortical anatomy, the two taxa are distinct. Microspermopteris is interpreted as a delicate, scrambling vine, liana, or shrublike plant in contrast to the more robust lyginopterids Lyginopteris, Schopfiastrum, and Heterangium

    Integrative paleobotany: Affirming the role of fossils in modern plant biology - Introduction and dedication

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    If you are interested in plant evolution, try this quick exercise: take a phylogenetic tree of the plant kingdom, close your eyes, and point your finger randomly to a node of the phylogeny. Irrespective of the clade to which you are pointing, there is one thing you should know about it: the living representatives of that clade have evolved as a result of a long process in which failed attempts are the rule, and as a result, the diversity of extinct forms accumulated in the fossil record far exceeds that recorded in the extant flora. From this simple concept, Gar W. Rothwell made his career. Because of that, here is a second thing you should know about the plant clade to which you pointed at random: Gar has, more likely than not, contributed information about evolution in that clade at some point in his career. Gar was one of the principal contributors to the revival of paleobotany from a largely descriptive discipline to a vibrant field of investigation at the forefront of modern evolutionary sciences that contributes crucial insights into plant evolution, equal in importance to those provided by genetics and molecular biology. Because of this, the impact of Gar’s scientific contributions reaches far beyond the field of paleobotany, with important implications for wide areas of plant biology, including anatomy and morphology, development, systematics, phylogeny, and evolution. Gar earned a master’s degree in the laboratory of Thomas N. Taylor (University of Illinois at Chicago, 1966) studying Paleozoic seeds in the genus Conostoma (Rothwell and Eggert 1970; Rothwell 1971a). He subsequently earned his PhD degree in the laboratory of Wilson N. Stewart (University of Alberta, 1973), where he reconstructed the plants in the seed fern genus Callistophyton (Rothwell 1972b, 1975, 1980, 1981). His work was instrumental in ushering in studies of fossil plants as whole living organisms, looking at both structure and development. These early experiences launched Gar on a career in plant evolutionary biology that stretched over a half century, during which he occupied positions at the University of Alberta, University of London–Chelsea College, Ohio University, and Oregon State University. Throughout his career, Gar’s scholarly work and contributions have been recognized by numerous awards and honors: the Isabel Cookson Award, the Edgar T. Wherry Award, the Michael A. Cichan Award, the Merit Award of the Botanical Society of America, and honorary membership in the International Organization of Palaeobotany, where he served for 12 years as secretary-treasurer and president.Fil: Escapa, Ignacio Hernán. Museo Paleontológico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Tomescu, Alexandru M. F.. Humboldt State University. Department of Biological Sciences; Estados UnidosFil: Dunn, Michael T.. Cameron University. Department of Agriculture, Biology and Health Science; Estados UnidosFil: Stockey, Ruth A.. State University of Oregon; Estados Unido
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