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Alan R Hemsley - One of the best experts on this subject based on the ideXlab platform.
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A Mid Devonian seed-Megaspore from East Greenland and the origin of the seed plants
Palaeontology, 2003Co-Authors: John E. A. Marshall, Alan R HemsleyAbstract:A new species of late Mid Devonian seed-Megaspore from East Greenland is described and named as Spermasporites allenii. The formerly monotypic genus Spermasporites is emended to accommodate this new species. Rare specimens of S. allenii, with near complete sporangial contents, occur together with specimens showing proximally adhering microspores. These demonstrate that S. allenii was contained within a sporangium exhibiting extreme anisospory, which is interpreted here as functionally bisexual. This is a key element in understanding its reproductive function. The Megaspore was shed along with some attached microspores giving it potential for both cross- and self-fertilization. This confers the advantages of heterospory without recourse to separate micro- and megasporangia. This provides a more likely mechanism for seed plant origin than the archaeopteridalean sporangium reduction model. Ultrastructural study of the Megaspore wall confirms the progymnosperm affinity of S. allenii. Comparable forms include the Frasnian Spermasporites devonicus and the Famennian seed-Megaspores isolated from Archaeosperma arnoldii.
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diversity of exine structure in upper carboniferous westphalian selaginellalean Megaspores
Review of Palaeobotany and Palynology, 2000Co-Authors: C F Cottnam, Alan R Hemsley, Margaret E. Collinson, R Rossler, Anthony P. R. BrainAbstract:Abstract Studies of wall structure in Mesozoic and Recent selaginellalean Megaspores have been well documented. However, Palaeozoic examples have received minimal attention. The principal Palaeozoic Megaspore genus of likely selaginellalean affinity is Triangulatisporites, extending from the Upper Devonian to the Upper Carboniferous. The particulate wall ultrastructure of a previously published Carboniferous (Duckmantian) Megaspore assigned to this genus suggested that this form of wall construction may have been the ancestral wall structure of the group, an observation which posed difficulties in relating selaginellalean ultrastructure to that of other contemporaneous lycopsid Megaspores. Subsequent investigation showed that the genus also contains more laminate exines similar to those of other extinct lycopsids and extant Selaginella species. Our new examples of Triangulatisporites ultrastructure from the Langsettian, Duckmantian and Westphalian D yield more information regarding early variation of wall structure within Carboniferous selaginellalean Megaspores and suggest that a more laminate wall composition is at least as old as the particulate form. However, without further investigation of Lower Carboniferous forms, we are unable to state which is indeed ancestral. The laminate structure reported here and elsewhere is, none the less, more easily related to comparable ultrastructure in other groups of Carboniferous lycopsid Megaspores and could suggest a link with such genera as Zonalesporites and early Lagenicula. This would be in keeping with current concepts regarding the most primitive ultrastructural type within lycopsid Megaspore walls.
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experimental modelling of exine self assembly
Botanical Journal of the Linnean Society, 1996Co-Authors: Alan R Hemsley, Paul D Jenkins, Margaret E. Collinson, Brian VincentAbstract:Living and fossil Megaspores produced bySelaginella(Lycopsida) and its extinct ancestors form distinctive (and occasionally iridescent) exines. Ultrastructural studies of these spores have provided data that demonstrate a colloidal mode of development which in turn implies a degree of self-assembly in the construction of these exines. We present here experimental evidence in support of the theory of selaginellalean Megaspore exine construction by depletion flocculation. Iridescent colloidal flocculations of polystyrene latex particles demonstrate an ultrastructural organization virtually indistinguishable from that of the biological system, and clearly demonstrate that self-assembly of complexSelaginellaexines by a relatively simple construction process is plausible.
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controls upon the ultrastructural preservation of sporinite
Fuel, 1993Co-Authors: Andrew C Scott, Alan R HemsleyAbstract:Abstract Ultrastructural studies using SEM and TEM have been undertaken on several Carboniferous Megaspores. Langenicula crassiaculeata Zerndt has been obtained from several facies at Lower Carboniferous localities in Scotland including limestones and shales. Both have had a similar thermal history. Tuberculatisporites spp. has been obtained from coals, shales and oolitic ironstones from the Westphalian B of Yorkshire, again having similar thermal histories. Ultrastructural preservation of the same species from different facies varies considerably. Excellent preservation has been observed in spores from facies which underwent early diagenetic cementation. It is concluded that compression rather than rank (temperature) is the main control of ultrastructural preservation of Megaspore exines. The methods of scanning acoustic microscopy, for the study of ultrastructure in Megaspores from sequences of high rank, and laser scanning microscopy for the study of Megaspores in coal, sediment, polished blocks or thin sections are presented.
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caudatosporites gen nov a re appraisal of an anomalous carboniferous lycopod seed Megaspore with reference to exine ultrastructure
Review of Palaeobotany and Palynology, 1991Co-Authors: Alan R Hemsley, Katherine M BartramAbstract:Abstract The Carboniferous lycopod seed-Megaspore formerly known as Cystosporites verrucosus Dijkstra (1946) or Lagenicula saccata Arnold (1950) is investigated using Light microscopy, SEM and TEM. The results of this investigation demonstrate a number of important differences between this spore and members of the genera into which it has previously been placed. In view of these differences and the phylogenetic implications of our results, the genus Caudatosporites gen. nov. is erected to include Lagenicula -like seed-Megaspores with an enclosing spongy wing.
Deming Wang - One of the best experts on this subject based on the ideXlab platform.
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changxingia longifolia gen et sp nov a new lycopsid from the late devonian of zhejiang province south china
Review of Palaeobotany and Palynology, 2014Co-Authors: Deming Wang, Meicen Meng, Jinzhuang Xue, James F Basinger, Yun Guo, Le LiuAbstract:Abstract Changxingia longifolia gen. et sp. nov. is described from the Upper Devonian Wutong Formation, Changxing County, northern Zhejiang Province, China. It possesses dichotomous axes, linear and smooth sterile leaves, rhomboidal leaf cushions with ligule pits and oval–oblanceolate leaf scars, and terminal sterile shoots or probable megasporangiate strobili. Leaves may have been persistent or not. Leaf cushions or bases bearing a ridge are helically arranged in parastichies on wide axes. Smooth megasporophylls with vertically expanded base borne in helices include a pedicel, a heel and an upturned linear lamina. The pedicel consists of a distinct keel and horizontal alations and the lamina has the distal part reflexed abaxially. A single ellipsoidal and sessile megasporangium occurs on the adaxial side of the pedicel and produces Lagenicula -type Megaspores with delicate spines. Changxingia may be assigned to the Dichostrobiles of the Isoёtales sensu lato and is compared with related taxa of the Late Palaeozoic. Fertile units (megasporophyll–sporangium complexes) are interpreted to have functioned as spore dispersal units. Heterosporous lycopsids with monosporangiate strobili are scarce in the Devonian, and Changxingia thus contributes to understanding of their early evolutionary history and Megaspore dispersal mechanisms.
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new insights and evolutionary significance of the megasporangiate strobilus of minostrobus chaohuensis lycopsida from the upper devonian of south china
Review of Palaeobotany and Palynology, 2013Co-Authors: Meicen Meng, Deming WangAbstract:Abstract Heterosporous lycopsids with monosporangiate strobili are highly diverse in the Carboniferous, but their early evolution is poorly understood. The Late Devonian Minostrobus chaohuensis was included in this plant group, but features of the strobili were unclear in detail. Permineralized material of M. chaohuensis was sectioned and ground in series to reveal details of megasporangiate strobili. The megasporophylls are smooth and borne in a 2/9 helical phyllotaxy. The megasporophyll consists of a pedicel which bears a keel and alations, lamina and heel. The alations extend horizontally and then bend upward to surround the sporangial base. A single megasporangium with a subarchesporial pad is inserted onto the sporophyll pedicel through a narrow attachment. Each sporangium contains four Lagenicula-type spiny Megaspores that may be of variable size. On the basis of these new fertile traits, M. chaohuensis is assigned to the Isoёtales sensu lato. This plant is proved to be monosporangiate, and thus Devonian lycopsids are shown for the first time to have possessed megasporangiate strobili. It is confirmed that phylogenetically advanced heterosporous lycopsids with monosporangiate strobili had evolved by the Late Devonian. The type of alations and size variation of the four Megaspores per sporangium indicate that Minostrobus may represent an evolutionary form in transition toward the Carboniferous isoёtaleans with monosporic megasporangia more fully enclosed by alations. Evidence suggests a free Megaspore dispersal mechanism in M. chaohuensis.
David J. Batten - One of the best experts on this subject based on the ideXlab platform.
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Megaspores and associated palynofloras of Middle Jurassic fluvio-deltaic sequences in North Yorkshire and the northern North Sea: a biofacies-based approach to palaeoenvironmental analysis and modelling
Journal of Micropalaeontology, 2016Co-Authors: Peter H. Morris, David J. BattenAbstract:Outcrops of the Early Bajocian, Gristhorpe Member (Ravenscar Group) in North Yorkshire have been subjected to a multi-disciplinary analysis which establishes a key reference section at Yons Nab. Eight micro-biofaces types (MBs) are defined based on counts of transitional marine microfaunas, Megaspores and plant-derived debris. Associated palynofloral associations (PAs) are used to qualify the micro-biofacies defined to provide an integrated model for interpreting salinity–freshwater trends associated with deltaic progradation and retreat. Megaspore and small-spore trends within the delta-plain are shown to have been closely linked to peat-mires forming in topographic lows, with variations across the delta-plain attributable to the presence of the semi-permanent and seasonal water tables. A reconstruction of the floodplain–peat-mire depositional setting is proposed where the composition of host vegetation (e.g. ferns, lycopsids) varied in relation to groundwater levels. Biostratigraphic correlation within the Gristhorpe Member is attempted using the base of ‘established’ delta-plain deposition (Megaspore dominant MBs/spore-dominant PAs) and the top and base agglutinated foraminifera-dominant MBs (brackish). Using these criteria the Gristhorpe Member is modelled in terms of a southward progradation of delta-plain facies into a bay-fill sequence, which persisted at Yons Nab. With the delta-plain established, the MB/PA trends and sedimentology suggest a northward shift towards the higher delta-plain, with seasonal standing water only. The MB/PA model was tested on core samples from the coeval lower Brent Group from northern North Sea well 34/10-B-12 (Gullfaks Field); MB/PA trends are shown to compare closely with those of the Gristhorpe Member at Yons Nab, with the same Megaspore/small-spore associations developed within similar lithofacies. On this basis transitional marine, bay-fill and delta-plain deposition are defined in the cored section. These comparative data suggest that the dispersal of Megaspore and miospore host floras occurred effectively across the Mid North Sea High, and that they colonized the same niche habitats associated with bay-fill and delta-plain development.
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morphology and wall ultrastructure of a new and highly distinctive Megaspore from the middle jurassic of yorkshire uk
Review of Palaeobotany and Palynology, 2015Co-Authors: Sam M Slater, David J. Batten, Wilson A Taylor, Christopher R Hill, Charles H WellmanAbstract:Abstract We describe a new and rather unusual Megaspore recovered from Middle Jurassic terrestrial deposits of Yorkshire, England that we name Reticuspinosporites whytei gen. et sp. nov. The contact area is non-trilete and is formed where an outer sculptured layer has not developed. This outer layer covers the remainder of the Megaspore and bears novel sculpture consisting of a highly irregular reticulum with areas ‘infilled’ to form plateaus that bear long spines. Analysis of wall ultrastructure reveals a four-layered wall comprising from inside to outside: (i) innermost, separated lamina; (ii) inner homogeneous layer; (iii) central spongy layer; and (iv) outermost homogeneous layer that forms the sculpture. Wall ultrastructure is not entirely diagnostic but is most suggestive of lycopsid affinities. Unusually the Megaspores commonly occur in pairs. They are not attached at their contact faces but by their equatorial or distal surfaces through entanglement of their spines. We interpret this feature as possibly an adaptation for floating and transport by water.
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Megaspores and Microspores of the Extant and Paleogene Marsileaceous Fern Regnellidium and Cretaceous Molaspora: Evolutionary and Phytogeographic Implications
International Journal of Plant Sciences, 2011Co-Authors: David J. Batten, Margaret E. Collinson, Anthony P. R. BrainAbstract:In common with the single extant species of the water fern Regnellidium, Regnellidium diphyllum, Megaspores of Eocene and Oligocene representatives of this genus are characterized by having twisted, leaflike folds forming an acrolamella around the triradiate suture. The fossil and modern Megaspores also have very similar wall ultrastructure and sculpture, and the morphology of the attached microspores of both is indistinguishable. Specimens of one of the species of the Cretaceous Megaspore genus Molaspora—namely, Molaspora lobata, with attached microspores from Spain—and spores in the sporocarp Regnellidium upatoiensis from Georgia, United States, share some characters with those of extant Regnellidium, but the surface ornament of the microspores and the ultrastructure of the Megaspore and microspore walls are different. The inner layer of the inner perine of M. lobata Megaspores is thinner than the outer layer and of more compact, spongiose construction than that of Eocene and Oligocene Regnellidium spor...
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Megaspore assemblages from the are formation rhaetian pliensbachian offshore mid norway and their value as field and regional stratigraphical markers
Journal of Micropalaeontology, 2009Co-Authors: Peter H. Morris, Alex Cullum, Martin A Pearce, David J. BattenAbstract:A Megaspore biozonation of the non-marine Are Formation is proposed, based on a micropalaeontological analysis of key Haltenbanken area wells (Block 6608/11). The lower part of the Are Formation is divisible into Banksisporites pinguis , Nathorstisporites hopliticus and Horstisporites areolatus zones, and subzones, occupying the Rhaetian–Hettangian interval. In the upper Are Formation a marked turnover of Megaspore assemblages is evident, with the appearance of several species of Trileites and the mesofossil Kuqaia quadrata . On this basis, the biozonation is extended into the Sinemurian–Pliensbachian, with the recognition of the Kuqaia quadrata Zone and subzones. Reference to selected wells in the Urd Field (Block 6608/10) and further south demonstrates that these biozones correlate across the northern Haltenbanken region. Biozonal boundaries are calibrated with miospore/microplankton markers where possible, to provide a robust bio-chronostratigraphical framework with which to evaluate the stratigraphy of the Are Formation and its reservoir units. Comparison with published European biostratigraphical data shows that a similar Megaspore succession exists through the Rhaeto-Liassic interval, with shifts in Megaspore composition occurring within the same time intervals. On this evidence it is suggested that the Megaspore biozones identified are regionally extensive and may reflect palaeoclimatic controls on the distribution of the Megaspore-producing plants. It is concluded that Megaspores are a stratigraphically important microfossil group, which should be utilized routinely in Upper Triassic–Jurassic oil field and regional biostratigraphical studies.
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Ultrastructural interpretation of the Late Cretaceous Megaspore Glomerisporites pupus and its associated microspores.
American journal of botany, 1998Co-Authors: David J. Batten, Margaret E. Collinson, Anthony P. R. BrainAbstract:The ultrastructure of the Late Cretaceous (Santonian‐?early Campanian) Megaspore Glomerisporites pupusand its associated microspores has been examined in an attempt to resolve a number of problems concerning the interpretation of their morphology. The new observations presented are based on an analysis of entire, fragmentary, and thin-sectioned specimens under scanning and transmission electron microscopes. These add to, and partly correct, previous observations on this taxon. They include the following: (1) The exine of the Megaspore consists of thin, homogeneous, outer undulating and inner electron dense layers, with a thicker zone of spongy structure in-between. (2) The perispore (or perine) of the Megaspore comprises four layers, in order towards the exterior: loose filamentous, dense filamentous, vacuolate, and columnar. (3) This is completely enclosed by a thick mat of hairs, which appears to be attached to the underlying perisporal layers by means of connections with a few of the ‘‘spines’’ that originate from the dense filamentous zone, and with some elements of the columnar perine. (4) The tripartite neck (acrolamella) of the spore, which is hidden beneath the mat of hairs, is predominantly an extension of the dense filamentous and vacuolate layers, but also involves the columnar layer, especially in the lower part. (5) Some of the numerous small floats that are embedded in the mat have hairs originating from them. (6) Both long tangled and circinate hairs surround the perispore of the microspores. (7) The exine of the microspore was at least partly attached to the perispore when the organ was viable. (8) It comprises four zones that vary in structure and electron density. These facts and comparisons made with other Megaspores and their associated microspores confirm evolutionary links between G. pupus and several taxa included within the Salviniaceae (Azolla, Parazolla, Salvinia) and possible ancestors of this group (the parent plants of Ariadnaesporites and Capulisporites).
Anthony P. R. Brain - One of the best experts on this subject based on the ideXlab platform.
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Megaspores and Microspores of the Extant and Paleogene Marsileaceous Fern Regnellidium and Cretaceous Molaspora: Evolutionary and Phytogeographic Implications
International Journal of Plant Sciences, 2011Co-Authors: David J. Batten, Margaret E. Collinson, Anthony P. R. BrainAbstract:In common with the single extant species of the water fern Regnellidium, Regnellidium diphyllum, Megaspores of Eocene and Oligocene representatives of this genus are characterized by having twisted, leaflike folds forming an acrolamella around the triradiate suture. The fossil and modern Megaspores also have very similar wall ultrastructure and sculpture, and the morphology of the attached microspores of both is indistinguishable. Specimens of one of the species of the Cretaceous Megaspore genus Molaspora—namely, Molaspora lobata, with attached microspores from Spain—and spores in the sporocarp Regnellidium upatoiensis from Georgia, United States, share some characters with those of extant Regnellidium, but the surface ornament of the microspores and the ultrastructure of the Megaspore and microspore walls are different. The inner layer of the inner perine of M. lobata Megaspores is thinner than the outer layer and of more compact, spongiose construction than that of Eocene and Oligocene Regnellidium spor...
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diversity of exine structure in upper carboniferous westphalian selaginellalean Megaspores
Review of Palaeobotany and Palynology, 2000Co-Authors: C F Cottnam, Alan R Hemsley, Margaret E. Collinson, R Rossler, Anthony P. R. BrainAbstract:Abstract Studies of wall structure in Mesozoic and Recent selaginellalean Megaspores have been well documented. However, Palaeozoic examples have received minimal attention. The principal Palaeozoic Megaspore genus of likely selaginellalean affinity is Triangulatisporites, extending from the Upper Devonian to the Upper Carboniferous. The particulate wall ultrastructure of a previously published Carboniferous (Duckmantian) Megaspore assigned to this genus suggested that this form of wall construction may have been the ancestral wall structure of the group, an observation which posed difficulties in relating selaginellalean ultrastructure to that of other contemporaneous lycopsid Megaspores. Subsequent investigation showed that the genus also contains more laminate exines similar to those of other extinct lycopsids and extant Selaginella species. Our new examples of Triangulatisporites ultrastructure from the Langsettian, Duckmantian and Westphalian D yield more information regarding early variation of wall structure within Carboniferous selaginellalean Megaspores and suggest that a more laminate wall composition is at least as old as the particulate form. However, without further investigation of Lower Carboniferous forms, we are unable to state which is indeed ancestral. The laminate structure reported here and elsewhere is, none the less, more easily related to comparable ultrastructure in other groups of Carboniferous lycopsid Megaspores and could suggest a link with such genera as Zonalesporites and early Lagenicula. This would be in keeping with current concepts regarding the most primitive ultrastructural type within lycopsid Megaspore walls.
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Ultrastructural interpretation of the Late Cretaceous Megaspore Glomerisporites pupus and its associated microspores.
American journal of botany, 1998Co-Authors: David J. Batten, Margaret E. Collinson, Anthony P. R. BrainAbstract:The ultrastructure of the Late Cretaceous (Santonian‐?early Campanian) Megaspore Glomerisporites pupusand its associated microspores has been examined in an attempt to resolve a number of problems concerning the interpretation of their morphology. The new observations presented are based on an analysis of entire, fragmentary, and thin-sectioned specimens under scanning and transmission electron microscopes. These add to, and partly correct, previous observations on this taxon. They include the following: (1) The exine of the Megaspore consists of thin, homogeneous, outer undulating and inner electron dense layers, with a thicker zone of spongy structure in-between. (2) The perispore (or perine) of the Megaspore comprises four layers, in order towards the exterior: loose filamentous, dense filamentous, vacuolate, and columnar. (3) This is completely enclosed by a thick mat of hairs, which appears to be attached to the underlying perisporal layers by means of connections with a few of the ‘‘spines’’ that originate from the dense filamentous zone, and with some elements of the columnar perine. (4) The tripartite neck (acrolamella) of the spore, which is hidden beneath the mat of hairs, is predominantly an extension of the dense filamentous and vacuolate layers, but also involves the columnar layer, especially in the lower part. (5) Some of the numerous small floats that are embedded in the mat have hairs originating from them. (6) Both long tangled and circinate hairs surround the perispore of the microspores. (7) The exine of the microspore was at least partly attached to the perispore when the organ was viable. (8) It comprises four zones that vary in structure and electron density. These facts and comparisons made with other Megaspores and their associated microspores confirm evolutionary links between G. pupus and several taxa included within the Salviniaceae (Azolla, Parazolla, Salvinia) and possible ancestors of this group (the parent plants of Ariadnaesporites and Capulisporites).
Meicen Meng - One of the best experts on this subject based on the ideXlab platform.
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changxingia longifolia gen et sp nov a new lycopsid from the late devonian of zhejiang province south china
Review of Palaeobotany and Palynology, 2014Co-Authors: Deming Wang, Meicen Meng, Jinzhuang Xue, James F Basinger, Yun Guo, Le LiuAbstract:Abstract Changxingia longifolia gen. et sp. nov. is described from the Upper Devonian Wutong Formation, Changxing County, northern Zhejiang Province, China. It possesses dichotomous axes, linear and smooth sterile leaves, rhomboidal leaf cushions with ligule pits and oval–oblanceolate leaf scars, and terminal sterile shoots or probable megasporangiate strobili. Leaves may have been persistent or not. Leaf cushions or bases bearing a ridge are helically arranged in parastichies on wide axes. Smooth megasporophylls with vertically expanded base borne in helices include a pedicel, a heel and an upturned linear lamina. The pedicel consists of a distinct keel and horizontal alations and the lamina has the distal part reflexed abaxially. A single ellipsoidal and sessile megasporangium occurs on the adaxial side of the pedicel and produces Lagenicula -type Megaspores with delicate spines. Changxingia may be assigned to the Dichostrobiles of the Isoёtales sensu lato and is compared with related taxa of the Late Palaeozoic. Fertile units (megasporophyll–sporangium complexes) are interpreted to have functioned as spore dispersal units. Heterosporous lycopsids with monosporangiate strobili are scarce in the Devonian, and Changxingia thus contributes to understanding of their early evolutionary history and Megaspore dispersal mechanisms.
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new insights and evolutionary significance of the megasporangiate strobilus of minostrobus chaohuensis lycopsida from the upper devonian of south china
Review of Palaeobotany and Palynology, 2013Co-Authors: Meicen Meng, Deming WangAbstract:Abstract Heterosporous lycopsids with monosporangiate strobili are highly diverse in the Carboniferous, but their early evolution is poorly understood. The Late Devonian Minostrobus chaohuensis was included in this plant group, but features of the strobili were unclear in detail. Permineralized material of M. chaohuensis was sectioned and ground in series to reveal details of megasporangiate strobili. The megasporophylls are smooth and borne in a 2/9 helical phyllotaxy. The megasporophyll consists of a pedicel which bears a keel and alations, lamina and heel. The alations extend horizontally and then bend upward to surround the sporangial base. A single megasporangium with a subarchesporial pad is inserted onto the sporophyll pedicel through a narrow attachment. Each sporangium contains four Lagenicula-type spiny Megaspores that may be of variable size. On the basis of these new fertile traits, M. chaohuensis is assigned to the Isoёtales sensu lato. This plant is proved to be monosporangiate, and thus Devonian lycopsids are shown for the first time to have possessed megasporangiate strobili. It is confirmed that phylogenetically advanced heterosporous lycopsids with monosporangiate strobili had evolved by the Late Devonian. The type of alations and size variation of the four Megaspores per sporangium indicate that Minostrobus may represent an evolutionary form in transition toward the Carboniferous isoёtaleans with monosporic megasporangia more fully enclosed by alations. Evidence suggests a free Megaspore dispersal mechanism in M. chaohuensis.