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Hagen Hass - One of the best experts on this subject based on the ideXlab platform.
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Endophytic cyanobacteria in a 400-million-yr-old land plant: A scenario for the origin of a symbiosis?
Review of Palaeobotany and Palynology, 2008Co-Authors: Michael Krings, Thomas N Taylor, Hans Kerp, Hagen Hass, Reinhard Agerer, Nora DotzlerAbstract:article Direct evidence for the origin and evolution of land plant/cyanobacterial symbioses is virtually absent from the fossil record. Here we report on rare occurrences of prostrate mycorrhizal axes of the Early Devonian land plant Aglaophyton major that host a filamentous cyanobacterium, which enters the plant through the stomata and colonizes the substomatal chambers and intercellular spaces in the outer cortex. In dead ends of the intercellular system, the filaments form loops and continue growth in reverse direction. Some filaments penetrate parenchyma cells close to and within the mycorrhizal arbuscule-zone and form intracellular coils. This discovery represents the earliest direct evidence for cyanobacteria growing inside land plants, and offers a model for the types of associations that may have preceded the evolution of mutualistic land plant/ cyanobacterial symbioses.
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Palaeonema phyticum gen. n., sp. n. (Nematoda: Palaeonematidae fam. n.), a Devonian nematode associated with early land plants
Nematology, 2008Co-Authors: Hagen Hass, Hans Kerp, George PoinarAbstract:Nematodes are one of the most abundant groups of invertebrates on the face of the earth. Their extremely poor fossil record hinders our ability to assess just when members of this group invaded land and first became associated with plants. This study reports fossil nematodes from the stomatal chambers of the Early Devonian (396 mya) land plant, Aglaophyton major. These nematodes, which are tentatively assigned to the order Enoplia, are described as Palaeonema phyticum gen. n., sp. n. in the new family Palaeonematidae fam. n. Diagnostic characters of the family are: i) cuticular striations; ii) uniform, cylindrical pharynx with the terminal portion only slightly set off from the remainder; and iii) a two-portioned buccal cavity with the upper portion bearing protuberances. The presence of eggs, juveniles and adults in family clusters within the plant tissues provide the earliest evidence of an association between terrestrial plants and animals and may represent an early stage in the evolution of plant parasitism by nematodes.
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An Alternative Mode of Early Land Plant Colonization by Putative Endomycorrhizal Fungi
Plant signaling & behavior, 2007Co-Authors: Michael Krings, Thomas N Taylor, Hans Kerp, Hagen Hass, Nora Dotzler, Elizabeth J. HermsenAbstract:Rhizomatous axes of Nothia aphylla, a land plant from the 400-myr-old Rhynie chert, host a fungus that closely resembles Glomites rhyniensis (Glomeromycota), the endomycorrhizal fungus of the Rhynie chert plant Aglaophyton major. However, G. rhyniensis is an intercellular endophyte that becomes intracellular exclusively within a well-defined region of the cortex, while the fungus in N. aphylla initially is intracellular but later becomes intercellular in the cortex. We hypothesize that N. aphylla displays an alternative mode of colonization by endomycorrhizal fungi, perhaps related to the peculiar internal anatomy of the lower portion of the rhizomatous axis, in which the radial arrangement of cells, along with the virtual absence of intercellular spaces, provides no intercellular infection pathway into the cortex.
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Spores of the Rhynie chert plant Aglaophyton (Rhynia) major (Kidston and Lang) D.S. Edwards, 1986
Review of Palaeobotany and Palynology, 2006Co-Authors: Charles H. Wellman, Hans Kerp, Hagen HassAbstract:Abstract Detailed studies have been undertaken on in situ spores of the Rhynie chert plant Aglaophyton (Rhynia) major (Kidston and Lang) D.S. Edwards. The in situ spores exhibit a variety of preservational types that are described. In several specimens, spores are exceptionally preserved: some apparently preserve an outer, enveloping, callose wall and others preserve the plasma membrane and possibly also cell contents. The in situ spores are relatively simple trilete spores with retusoid structure that are entirely laevigate and have a distinctive thinning associated with the trilete mark. They may be accommodated in the dispersed spore genus Retusotriletes . Identical spores occur dispersed in litter/soil horizons preserved in the chert (as individual spores, including germinating spores, in spore masses and in coprolites), and are also a common element of dispersed spore assemblages from throughout the stratigraphical sequence of the Rhynie outlier. The dispersed forms are placed with Retusotriletes sp. CW-A, as described by Wellman [Wellman, 2004. Palaeoecology and palaeophytogeography of the Rhynie chert plants: evidence from integrated analysis of in situ and dispersed spores. Proc. R. Soc. London, Ser. B 271, 985–992; Wellman, in press. Spore assemblages from the “Lower Old Red Sandstone” deposits of the Rhynie Outlier, Scotland. Trans. R. Soc. Edinburgh: Earth Sci.], and it is concluded that the dispersed spore taxon Retusotriletes sp. CW-A was produced by A. major . Integrated evidence from dispersed and in situ spores (particularly those exceptionally preserved) permits a detailed reconsideration of the many lines of evidence pertaining to the reproductive biology and ecology of the plant A. major .
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life history biology of early land plants deciphering the gametophyte phase
Proceedings of the National Academy of Sciences of the United States of America, 2005Co-Authors: Thomas N Taylor, Hans Kerp, Hagen HassAbstract:The ca. 400-million-year-old Rhynie chert biota represents a benchmark for studies of early terrestrial ecosystems. The exquisite preservation of the organisms documents an ancient biodiversity that also includes various levels of biological interaction. Absent from the picture until recently has been detailed information about the development of the gametophyte phase and the alternation of generations of the macroplants in this ecosystem. Here, we trace the development of the gametophyte phase of Aglaophyton, an early land plant with an unusual complement of structural and morphological characters. Mature gametophytes consist of a fleshy protocorm attached to the substrate by basal rhizoids; arising from the upper surface are one to several upright gametangiophores bearing multiple gametangia. Stomata are present on the upper surface of the protocorm and gametangiophore, and endomycorrhizal fungi extend throughout the gametophyte. Gametophytes are unisexual, producing either antheridiophores or archegoniophores. There is no evidence that gametophytes later become hermaphroditic. The sexual dimorphism of the Rhynie chert gametophytes is inconsistent with theoretical ideas about the haploid phase of early land plants. The gametophyte phase of early land plants can now be considered within an ecological and evolutionary framework that, in turn, can be used to develop hypotheses about some aspects of the population dynamics and growth of these early land plants.
Hans Kerp - One of the best experts on this subject based on the ideXlab platform.
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Endophytic cyanobacteria in a 400-million-yr-old land plant: A scenario for the origin of a symbiosis?
Review of Palaeobotany and Palynology, 2008Co-Authors: Michael Krings, Thomas N Taylor, Hans Kerp, Hagen Hass, Reinhard Agerer, Nora DotzlerAbstract:article Direct evidence for the origin and evolution of land plant/cyanobacterial symbioses is virtually absent from the fossil record. Here we report on rare occurrences of prostrate mycorrhizal axes of the Early Devonian land plant Aglaophyton major that host a filamentous cyanobacterium, which enters the plant through the stomata and colonizes the substomatal chambers and intercellular spaces in the outer cortex. In dead ends of the intercellular system, the filaments form loops and continue growth in reverse direction. Some filaments penetrate parenchyma cells close to and within the mycorrhizal arbuscule-zone and form intracellular coils. This discovery represents the earliest direct evidence for cyanobacteria growing inside land plants, and offers a model for the types of associations that may have preceded the evolution of mutualistic land plant/ cyanobacterial symbioses.
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Palaeonema phyticum gen. n., sp. n. (Nematoda: Palaeonematidae fam. n.), a Devonian nematode associated with early land plants
Nematology, 2008Co-Authors: Hagen Hass, Hans Kerp, George PoinarAbstract:Nematodes are one of the most abundant groups of invertebrates on the face of the earth. Their extremely poor fossil record hinders our ability to assess just when members of this group invaded land and first became associated with plants. This study reports fossil nematodes from the stomatal chambers of the Early Devonian (396 mya) land plant, Aglaophyton major. These nematodes, which are tentatively assigned to the order Enoplia, are described as Palaeonema phyticum gen. n., sp. n. in the new family Palaeonematidae fam. n. Diagnostic characters of the family are: i) cuticular striations; ii) uniform, cylindrical pharynx with the terminal portion only slightly set off from the remainder; and iii) a two-portioned buccal cavity with the upper portion bearing protuberances. The presence of eggs, juveniles and adults in family clusters within the plant tissues provide the earliest evidence of an association between terrestrial plants and animals and may represent an early stage in the evolution of plant parasitism by nematodes.
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An Alternative Mode of Early Land Plant Colonization by Putative Endomycorrhizal Fungi
Plant signaling & behavior, 2007Co-Authors: Michael Krings, Thomas N Taylor, Hans Kerp, Hagen Hass, Nora Dotzler, Elizabeth J. HermsenAbstract:Rhizomatous axes of Nothia aphylla, a land plant from the 400-myr-old Rhynie chert, host a fungus that closely resembles Glomites rhyniensis (Glomeromycota), the endomycorrhizal fungus of the Rhynie chert plant Aglaophyton major. However, G. rhyniensis is an intercellular endophyte that becomes intracellular exclusively within a well-defined region of the cortex, while the fungus in N. aphylla initially is intracellular but later becomes intercellular in the cortex. We hypothesize that N. aphylla displays an alternative mode of colonization by endomycorrhizal fungi, perhaps related to the peculiar internal anatomy of the lower portion of the rhizomatous axis, in which the radial arrangement of cells, along with the virtual absence of intercellular spaces, provides no intercellular infection pathway into the cortex.
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Spores of the Rhynie chert plant Aglaophyton (Rhynia) major (Kidston and Lang) D.S. Edwards, 1986
Review of Palaeobotany and Palynology, 2006Co-Authors: Charles H. Wellman, Hans Kerp, Hagen HassAbstract:Abstract Detailed studies have been undertaken on in situ spores of the Rhynie chert plant Aglaophyton (Rhynia) major (Kidston and Lang) D.S. Edwards. The in situ spores exhibit a variety of preservational types that are described. In several specimens, spores are exceptionally preserved: some apparently preserve an outer, enveloping, callose wall and others preserve the plasma membrane and possibly also cell contents. The in situ spores are relatively simple trilete spores with retusoid structure that are entirely laevigate and have a distinctive thinning associated with the trilete mark. They may be accommodated in the dispersed spore genus Retusotriletes . Identical spores occur dispersed in litter/soil horizons preserved in the chert (as individual spores, including germinating spores, in spore masses and in coprolites), and are also a common element of dispersed spore assemblages from throughout the stratigraphical sequence of the Rhynie outlier. The dispersed forms are placed with Retusotriletes sp. CW-A, as described by Wellman [Wellman, 2004. Palaeoecology and palaeophytogeography of the Rhynie chert plants: evidence from integrated analysis of in situ and dispersed spores. Proc. R. Soc. London, Ser. B 271, 985–992; Wellman, in press. Spore assemblages from the “Lower Old Red Sandstone” deposits of the Rhynie Outlier, Scotland. Trans. R. Soc. Edinburgh: Earth Sci.], and it is concluded that the dispersed spore taxon Retusotriletes sp. CW-A was produced by A. major . Integrated evidence from dispersed and in situ spores (particularly those exceptionally preserved) permits a detailed reconsideration of the many lines of evidence pertaining to the reproductive biology and ecology of the plant A. major .
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life history biology of early land plants deciphering the gametophyte phase
Proceedings of the National Academy of Sciences of the United States of America, 2005Co-Authors: Thomas N Taylor, Hans Kerp, Hagen HassAbstract:The ca. 400-million-year-old Rhynie chert biota represents a benchmark for studies of early terrestrial ecosystems. The exquisite preservation of the organisms documents an ancient biodiversity that also includes various levels of biological interaction. Absent from the picture until recently has been detailed information about the development of the gametophyte phase and the alternation of generations of the macroplants in this ecosystem. Here, we trace the development of the gametophyte phase of Aglaophyton, an early land plant with an unusual complement of structural and morphological characters. Mature gametophytes consist of a fleshy protocorm attached to the substrate by basal rhizoids; arising from the upper surface are one to several upright gametangiophores bearing multiple gametangia. Stomata are present on the upper surface of the protocorm and gametangiophore, and endomycorrhizal fungi extend throughout the gametophyte. Gametophytes are unisexual, producing either antheridiophores or archegoniophores. There is no evidence that gametophytes later become hermaphroditic. The sexual dimorphism of the Rhynie chert gametophytes is inconsistent with theoretical ideas about the haploid phase of early land plants. The gametophyte phase of early land plants can now be considered within an ecological and evolutionary framework that, in turn, can be used to develop hypotheses about some aspects of the population dynamics and growth of these early land plants.
Thomas N Taylor - One of the best experts on this subject based on the ideXlab platform.
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Endophytic cyanobacteria in a 400-million-yr-old land plant: A scenario for the origin of a symbiosis?
Review of Palaeobotany and Palynology, 2008Co-Authors: Michael Krings, Thomas N Taylor, Hans Kerp, Hagen Hass, Reinhard Agerer, Nora DotzlerAbstract:article Direct evidence for the origin and evolution of land plant/cyanobacterial symbioses is virtually absent from the fossil record. Here we report on rare occurrences of prostrate mycorrhizal axes of the Early Devonian land plant Aglaophyton major that host a filamentous cyanobacterium, which enters the plant through the stomata and colonizes the substomatal chambers and intercellular spaces in the outer cortex. In dead ends of the intercellular system, the filaments form loops and continue growth in reverse direction. Some filaments penetrate parenchyma cells close to and within the mycorrhizal arbuscule-zone and form intracellular coils. This discovery represents the earliest direct evidence for cyanobacteria growing inside land plants, and offers a model for the types of associations that may have preceded the evolution of mutualistic land plant/ cyanobacterial symbioses.
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An Alternative Mode of Early Land Plant Colonization by Putative Endomycorrhizal Fungi
Plant signaling & behavior, 2007Co-Authors: Michael Krings, Thomas N Taylor, Hans Kerp, Hagen Hass, Nora Dotzler, Elizabeth J. HermsenAbstract:Rhizomatous axes of Nothia aphylla, a land plant from the 400-myr-old Rhynie chert, host a fungus that closely resembles Glomites rhyniensis (Glomeromycota), the endomycorrhizal fungus of the Rhynie chert plant Aglaophyton major. However, G. rhyniensis is an intercellular endophyte that becomes intracellular exclusively within a well-defined region of the cortex, while the fungus in N. aphylla initially is intracellular but later becomes intercellular in the cortex. We hypothesize that N. aphylla displays an alternative mode of colonization by endomycorrhizal fungi, perhaps related to the peculiar internal anatomy of the lower portion of the rhizomatous axis, in which the radial arrangement of cells, along with the virtual absence of intercellular spaces, provides no intercellular infection pathway into the cortex.
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life history biology of early land plants deciphering the gametophyte phase
Proceedings of the National Academy of Sciences of the United States of America, 2005Co-Authors: Thomas N Taylor, Hans Kerp, Hagen HassAbstract:The ca. 400-million-year-old Rhynie chert biota represents a benchmark for studies of early terrestrial ecosystems. The exquisite preservation of the organisms documents an ancient biodiversity that also includes various levels of biological interaction. Absent from the picture until recently has been detailed information about the development of the gametophyte phase and the alternation of generations of the macroplants in this ecosystem. Here, we trace the development of the gametophyte phase of Aglaophyton, an early land plant with an unusual complement of structural and morphological characters. Mature gametophytes consist of a fleshy protocorm attached to the substrate by basal rhizoids; arising from the upper surface are one to several upright gametangiophores bearing multiple gametangia. Stomata are present on the upper surface of the protocorm and gametangiophore, and endomycorrhizal fungi extend throughout the gametophyte. Gametophytes are unisexual, producing either antheridiophores or archegoniophores. There is no evidence that gametophytes later become hermaphroditic. The sexual dimorphism of the Rhynie chert gametophytes is inconsistent with theoretical ideas about the haploid phase of early land plants. The gametophyte phase of early land plants can now be considered within an ecological and evolutionary framework that, in turn, can be used to develop hypotheses about some aspects of the population dynamics and growth of these early land plants.
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Four hundred-million-year-old vesicular arbuscular mycorrhizae
Proceedings of the National Academy of Sciences of the United States of America, 1994Co-Authors: Winfried Remy, Thomas N Taylor, Hagen Hass, Hans KerpAbstract:Abstract The discovery of arbuscules in Aglaophyton major, an Early Devonian land plant, provides unequivocal evidence that mycorrhizae were established >400 million years ago. Nonseptate hyphac and arbuscules occur in a specialized meristematic region of the cortex that continually provided new cells for fungal infection. Arbuscules are morphologically identical to those of living arbuscular mycorrhizae in consisting of a basal trunk and repeatedly branched bush-like tuft within the plant cell. Although interpretations of the evolution of mycorrhizal mutualisms continue to be speculative, the existence of arbuscules in the Early Devonian indicates that nutrient transfer mutualism may have been in existence when plants invaded the land.
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Fungi from the Lower Devonian Rhynie chert : chytridiomycetes
American Journal of Botany, 1992Co-Authors: Thomas N Taylor, Winfried Remy, Hagen HassAbstract:Several different chytridiomycetes are described from the Lower Devonian (Siegenian) Rhynie chert. Included are both eucarpic and apparently holocarpic forms that occur in Palaeonitel/a, Aglaophyton, Lyonophyton, Horneophyton, and clusters of algal cells, as well as in the surrounding chert matrix. Holocarpic types consist of endobiotic sporangia, each characterized by one discharge tube. Sporangia can be traced from the thallus stage to the discharge of zoospores. Monocentric and polycentric eucarpic chytrids are associated with the miospores of Aglaophyton and various thick-walled fungal spores. In these forms the sporangia are variable in size and shape ranging up to 30 jum. Most appear to be inoperculate and there is evidence that the sporangium ruptured on the distal surface. Some contain zoospores with flagella. One operculate eucarpic form had parasitized the cellular gametophyte emerging from the proximal surface of an Aglaophyton spore. Several of the Rhynie chert chytrids are comparable with a number of extant forms (e.g., Olpidiaceae and Spizellomycetaceae), while others possess features that encompass several groups. These fossil fungi are discussed in the context of their interactions with other organisms in this Lower Devonian freshwater paleoecosystem.
Dianne Edwards - One of the best experts on this subject based on the ideXlab platform.
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Embryophytic sporophytes in the Rhynie and Windyfield cherts
Transactions of the Royal Society of Edinburgh: Earth Sciences, 2003Co-Authors: Dianne EdwardsAbstract:ABSTRACTBrief descriptions and comments on relationships are given for the seven embryophytic sporophytes in the cherts at Rhynie, Aberdeenshire, Scotland. They are Rhynia gwynnevaughanii Kidston & Lang, Aglaophyton major D. S. Edwards, Horneophyton lignieri Barghoorn & Darrah, Asteroxylon mackiei Kidston & Lang, Nothia aphylla Lyon ex Høeg, Trichopherophyton teuchansii Lyon & Edwards and Ventarura lyonii Powell, Edwards & Trewin. The superb preservation of the silica permineralisations produced in the hot spring environment provides remarkable insights into the anatomy of early land plants which are not available from compression fossils and other modes of permineralisation. They include soft tissues, such as those surrounding stomata, rhizoids, apical and lateral meristems, and diversity in conducting cells, with inferences for palaeoecophysiology, including water use efficiency, transport and absorption, and for growth processes and patterns.
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The role of mid-palaeozoic mesofossils in the detection of early bryophytes.
Philosophical transactions of the Royal Society of London. Series B Biological sciences, 2000Co-Authors: Dianne EdwardsAbstract:Recently discovered Silurian and Devonian coalified mesofossils provide an additional source of data on early embryophytes. Those reviewed in this paper are considered of some relevance to understanding the early history of bryophytes while highlighting the difficulties of recognizing bryophytes in often very fragmentary fossils. The first group comprises sporophytes in which terminal sporangia contain permanent dyads and tetrads. Such spores (cryptospores) are similar to those found dispersed in older Ordovician and Silurian strata, when they are considered evidence for a land vegetation of embryophytes at a bryophyte grade. The phylogenetic significance of plants, where the axes associated with both dyad- and tetrad-containing sporangia are branching, a character state not found in extant bryophytes, is discussed. The second group comprises axial fossils, many with occasional stomata, in which central conducting strands include G-type tracheids and a number of novel types of elongate elements not readily compared with those of any tracheophyte. They include smooth-walled, evenly thickened elongate elements as well as those with numerous branching +/- anastomosing projections into the lumen. Some of the latter bear an additional microporate layer, but the homogenized lateral walls between adjacent cells are never perforate. Such cells, which occur in various combinations in central strands, are compared with the leptoids and hydroids of mosses, hydroids of liverworts and presumed water-conducting cells in coeval Lower Devonian plants such as Aglaophyton. It is concluded that lack of information on the chemistry of their walls hampers sensible assessment of their functions and the affinities of the plants. Finally, a minute fossil, comprising an elongate sporangium in which a central cylindrical cavity containing spores and possible elaters terminates in a complex poral dehiscence apparatus, is used to exemplify problems of identifying early bryophytes. It is concluded that further progress necessitates the discovery of pre-Upper Silurian fossils with well-preserved anatomy, as well as a re-evaluation of criteria used to assess existing and new Devonian fossils for bryophyte affinity.
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Novel conducting tissues in Lower Devonian plants
Botanical Journal of the Linnean Society, 2000Co-Authors: Dianne Edwards, L. AxeAbstract:Elongate cells presumed to comprise water-conducting tissues are described from the central regions of short lengths of two naked, stomatiferous, coalified, axial fossils from Lochkovian (Lower Devonian) fluvial rocks in the Welsh Borderland. In one, a discrete central strand is predominantly composed of uniformly thickened cells that are compared with central tissues in coeval plants, e.g. Aglaophyton, and the hydroids of extant mosses. The other has at least two types of cells with pits of plasmodesmata dimensions that perforate only the inner layer of a bilayered wall. These are compared with liverwort and Takakia hydroids and the coeval S-type tracheids that characterize the Rhyniopsida. The affinities of the two axes remain equivocal. The relevance of plasmodesmata-derived pits to the evolution of diversity in water-conducting elements in early cmbryophytes is discussed.
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Cells and tissues in the vegetative sporophytes of early land plants
New Phytologist, 1993Co-Authors: Dianne EdwardsAbstract:Remarkable preservation in coalified and pennineralized fossils from Upper Silurian and Lower Devonian sediments deposited some 420 to 390 million years ago provides insight into the major anatomical innovations associated with the early stages in the colonization of the land by higher plants. Using uniformitarian principles, such information, combined with gross morphology, can then be used to reconstruct the pioneers as growing, metabolizing and reproducing organisms, as well as allowing assessment of affinity, although apart from the lycophytes, they have no close relationship with extant groups. In considering vascular tissues, diversity is exemplified by descriptions of the metaxylem in protosteles of Zosterophyllopsida and Drepanophycopsida (putative lycophytes), of Psilophyton (Trimerophytopsida), of the Rhyniaceae (including Rhynia gwynnevaughanii, certain Taeniocrada spp., Sennicaulis) and of Cooksonia pertoni, a Lower Devonian representative of the organization found in the oldest pteridophyte-like land plants. Aglaophyton major is included as a plant with bryophyte-like vascular tissues in a branching sporophyte with cuticle, stomata and intercellular space system typical of the homoiohydric tracheophyte. In all water-conducting cells, interpretation of the primary and secondary wall results from comparisons involving the anatomy and chemistry of extant examples and an understanding of taphonomic processes. Phloem is only rarely preserved and usually identified from its position around the xylem. In contrast, dermal features are better known, because of penetration of the resilient cuticle between epidermal cells. They appear conservative. Thus stomata with two guard cells look remarkably similar to extant forms in surface view, and by consideration of their relationship with surrounding epidermal cells and of extent of cuticularization, seem to have operated in a similar way to those in certain mosses and ferns. Cuticular ornamentation (papillae, striations) and epidermal outgrowths (unicellular and multicellular) are described and their adaptive significance conjectured. Ground tissue systems are best preserved in Rhynie Chert permineralizations where zonation of the cortex is tentatively related to photosynthetic and structural roles. The latter function is also attributed to thick-walled, outer cortical cells recorded in many zosterophylls and in Psilophyton, although the chemical nature of the walls themselves remains equivocal. Problems of identification of roots in plants possessing axial organization with exarch xylem, and in leafy plants with smooth lateral branching systems are briefly addressed. Finally axis apices in Rhynia givynne-vaughanii and sections showing stages in the maturation of Asteroxylon stems are described from the Rhynie Chert.
Winfried Remy - One of the best experts on this subject based on the ideXlab platform.
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New information on gametophytes and sporophytes of Aglaophyton major and inferences about possible environmental adaptations
Review of Palaeobotany and Palynology, 1996Co-Authors: Winfried Remy, Hagen HassAbstract:Abstract Additional information on gametophytes and sporophytes of Aglaophyton major from the Early Devonian Rhynie chert leads to a much better understanding of many biological and ecological aspects of this early land plant. At least three early ontogenetic stages can be demonstrated, before aerial axes start to develop on the young gametophytes. Only the aerial axes show the essential features of a land plant (stomata, conducting tissue); the initial stages seem more likely adapted to shallow aquatic or edaphic humid than to fully terrestrial environmental conditions. Serial sections of aerial axes of gametophytes and sporophytes of Aglaophyton have yielded new histological and developmental features. These include cuticle structures, stomatal and substomatal features. A hitherto undescribed type of specialized cortical tissue, arrested apices, the formation of second-order axes and bulbil-like organs are documented. New observations on the development of rhizoidal bulges and wound-repair (including conducting) tissues complete this report. The new information provides additional evidence for life (competition) strategies in Aglaophyton , e.g. extensive renewing growth and vegetative propagation. It throws new light upon the adaptive behaviour of Aglaophyton , e.g. protection mechanisms against desiccation of aerial axes. It also illustrates considerable developmental biology of Aglaophyton .
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Four hundred-million-year-old vesicular arbuscular mycorrhizae
Proceedings of the National Academy of Sciences of the United States of America, 1994Co-Authors: Winfried Remy, Thomas N Taylor, Hagen Hass, Hans KerpAbstract:Abstract The discovery of arbuscules in Aglaophyton major, an Early Devonian land plant, provides unequivocal evidence that mycorrhizae were established >400 million years ago. Nonseptate hyphac and arbuscules occur in a specialized meristematic region of the cortex that continually provided new cells for fungal infection. Arbuscules are morphologically identical to those of living arbuscular mycorrhizae in consisting of a basal trunk and repeatedly branched bush-like tuft within the plant cell. Although interpretations of the evolution of mycorrhizal mutualisms continue to be speculative, the existence of arbuscules in the Early Devonian indicates that nutrient transfer mutualism may have been in existence when plants invaded the land.
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The Gametophyte Generation of Some Early Devonian Land Plants
International Journal of Plant Sciences, 1993Co-Authors: Winfried Remy, Patricia G. Gensel, Hagen HassAbstract:We summarize the current information on gametophytic plants from the Lower Devonian that are represented by three types based on permineralizations in the Rhynie Chert, two of which are antheridial (Lyonophyton and Kidstonophyton) and one that is archegoniate (Langiophyton). Impression and compression remains attributed to Sciadophyton and Calyculiphyton also are interpreted as gametophytic, based on their similarity to the permineralized forms. All are axial structures, with some axes terminating in cup-shaped gametangiophores on or in which gametangia occur, and all exhibit preserved cuticles with stomata and conducting tissue. Similarity in epidermal and conducting cell characters serves as a basis for postulating sporophyte relationships for the Rhynie Chert gametophytes as follows (N-2N): Lyonophyton-Aglaophyton, Kidstonophyton-Nothia, and Langiophyton-Horneophyton. Comparison with bryophytes and tracheophytes shows that these forms exhibit unique combinations of characters. They are more advanced th...
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Fungi from the Lower Devonian Rhynie chert : chytridiomycetes
American Journal of Botany, 1992Co-Authors: Thomas N Taylor, Winfried Remy, Hagen HassAbstract:Several different chytridiomycetes are described from the Lower Devonian (Siegenian) Rhynie chert. Included are both eucarpic and apparently holocarpic forms that occur in Palaeonitel/a, Aglaophyton, Lyonophyton, Horneophyton, and clusters of algal cells, as well as in the surrounding chert matrix. Holocarpic types consist of endobiotic sporangia, each characterized by one discharge tube. Sporangia can be traced from the thallus stage to the discharge of zoospores. Monocentric and polycentric eucarpic chytrids are associated with the miospores of Aglaophyton and various thick-walled fungal spores. In these forms the sporangia are variable in size and shape ranging up to 30 jum. Most appear to be inoperculate and there is evidence that the sporangium ruptured on the distal surface. Some contain zoospores with flagella. One operculate eucarpic form had parasitized the cellular gametophyte emerging from the proximal surface of an Aglaophyton spore. Several of the Rhynie chert chytrids are comparable with a number of extant forms (e.g., Olpidiaceae and Spizellomycetaceae), while others possess features that encompass several groups. These fossil fungi are discussed in the context of their interactions with other organisms in this Lower Devonian freshwater paleoecosystem.
