Devonian Plant Research Articles

New data about anatomy, branching, and inferred growth patterns in the Early Devonian plant Armoricaphyton chateaupannense, Montjean-sur-Loire, France

This study provides detailed information, based on serial peels, on the anatomy of the primary and secondary xylem, lateral branch formation, and proposed growth pattern of Armoricaphyton Strullu-Derrien et al., an Early Devonian (Pragian) basal euphyllophyte. The centrarch primary xylem strand is circular to oval in cross section and includes P-type tracheids. The pattern of lateral branch departure is described in detail based on serial peels. The secondary xylem, illustrated in transverse, radial and tangential longitudinal sections, includes P-type tracheids with similar pitting in radial and tangential walls. The presence of one-walled spaces interpreted as rays is confirmed. This study also documents the earliest occurrence of secondary xylem at bases of next higher order of branches. A model of growth for this unusual Early Devonian plant is presented, with documented epidogenetic, menetogenetic and possible apoxogenetic phases. The difference in proportion of primary to secondary xylem is postulated to be a result of this mode of growth. The possible implications of xylem size and organization in the lateral organ in Armoricaphyton relative to the early evolution of the megaphyllous leaf are briefly discussed.

InvestigatingDevonian trees as geo‐engineers of past climates: linking palaeosols to palaeobotany and experimental geobiology

AbstractWe present the rationale for a cross‐disciplinary investigation addressing the ‘Devonian plant hypothesis’ which proposes that the evolutionary appearance of trees with deep, complex rooting systems represents one of the major biotic feedbacks on geochemical carbon cycling during thePhanerozoic. According to this hypothesis, trees have dramatically enhanced mineral weathering driving an increased flux ofCa2+to the oceans and, ultimately, a 90% decline in atmosphericCO2levels through thePalaeozoic. Furthermore, experimental studies indicate a key role for arbuscular mycorrhizal fungi in soil–plant processes and especially in unlocking the limiting nutrient phosphorus in soil viaCa‐phosphate dissolution mineral weathering. This suggests co‐evolution of roots and symbiotic fungi since theEarlyDevonian could well have triggered positive feedbacks on weathering rates whereby root–fungalPrelease supports higher biomass forested ecosystems. Long‐standing areas of uncertainty in this paradigm include the following: (1) limited fossil record documenting the origin and timeline of the evolution of tree‐sized plants through theDevonian; and (2) the effects of the evolutionary advance of trees and theirin siturooting structures on palaeosol geochemistry. We are addressing these issues by integrating palaeobotanical studies with geochemical and mineralogical analyses of palaeosol sequences at selected sites across easternNorthAmerica with a particular focus on drill cores fromMiddleDevonian forests inGreeneCounty,NewYorkState.

The first Australian palynologist: Isabel Clifton Cookson (1893–1973) and her scientific work

Isabel Clifton Cookson (1893–1973) of Melbourne, Australia, was one of that country’s first professional woman scientists. She is remembered as one of the most eminent palaeontologists of the twentieth century and had a distinguished research career of 58 years, authoring or co-authoring 93 scientific publications. Isabel worked with great distinction on modern and fossil plants, and pioneered palynology in Australia. She was a consumate taxonomist and described, or jointly described, a prodigious total of 110 genera, 557 species and 32 subspecific taxa of palynomorphs and plants. Cookson was a trained biologist and initially worked as a botanist during the 1920s. At the same time she became interested in fossil plants and then, Mesozoic–Cenozoic terrestrial (1940s–1950s) and aquatic (1950s–1970s) palynomorphs. Cookson’s research into the late Silurian–Early Devonian plants of Australia and Europe, particularly the Baragwanathia flora, between the 1920s and the 1940s was highly influential in the field of early plant evolution. The fossil plant genus Cooksonia was named for Isabel in 1937 by her principal mentor in palaeobotany, Professor William H. Lang. From the 1940s Cookson focussed on Cenozoic floras and, with her students, elucidated floral affinities by comparative analyses of micromorphology, anatomy and in situ pollen/spores between fossil and extant taxa. This led to an interest in pre-Quaternary and Quaternary terrestrial pollen and spores; hence Isabel was the first palynologist in Australia. Her work on Paleogene and Neogene pollen and spores during the 1940s and 1950s provided incontrovertible evidence of the former widespread distribution of many important elements of Southern Hemisphere floras. During the early 1950s, while approaching her 60th year, Isabel turned her attention to marine palynomorphs. She worked with great distinction with Georges Deflandre and Alfred Eisenack, and also as a sole author, on acritarchs, dinoflagellate cysts and prasinophytes from the Jurassic to Quaternary of Australia and Papua New Guinea. She also co-authored papers on aquatic palynomorphs with Lucy M. Cranwell, Norman F. Hughes and Svein B. Manum. Isabel Cookson laid out the taxonomic basis for the study of Australasian Mesozoic and Cenozoic marine palynofloras by establishing, or jointly establishing, 76 genera and 386 species of marine microplankton. Her studies throughout her career, although especially in marine palynology, concentrated largely on taxonomy. However, she was one of the first palynologists to demonstrate the utility of dinoflagellate cysts for relative age dating and correlation in geological exploration.

Forania Plegiospinosa, gen. et sp. nov.: A Zosterophyll from the Early Devonian of New Brunswick, Canada, with a Novel Emergence Type

Premise of research. The zosterophylls are a group of primitive land plants that possess comparatively few characters useful in taxonomic distinction but vary considerably among these characters, such that a large number of genera and species are currently recognized. We studied specimens of a novel Early Devonian plant from New Brunswick, Canada, that further extends known variation within Zosterophyllopsida sensu Kenrick and Crane. After careful reevaluation of character and character-state utility in taxonomic circumscription among these simple early plants, we recognize this plant as a new genus and species, Forania plegiospinosa. Methodology. Preserved as adpressions, specimens were prepared with the standard paleobotanical techniques of dégagement and maceration, with appropriate parts figured via LM. Pivotal results. Forania plegiospinosa is interpreted to be a decumbent plant, bearing stout, mostly retrorsely curved, spine-like emergences arranged in two rows along the axes, variable modes of branching, circinately coiled axes, lateral buds, and sparsely scattered, circular to reniform lateral sporangia. Cuticular features of this species include polygonal epidermal cells and anomocytic sporangia. This plant provides the first documented evidence of stomata on emergences. The presence of stomata on the bases of large emergences suggests that emergence volume is a factor in stomatal location and development. Conclusions. Criteria for establishing new genera are discussed in the context of the mosaic of characters found among these early plants. Forania exhibits a unique combination of characters that is consistent with other zosterophylls at the generic level. It best fits within the Sawdoniaceae sensu Kenrick and Crane, although its sporangia are solitary rather than in two rows.

Earliest record of megaphylls and leafy structures, and their initial diversification

Evolutionary changes in the structure of leaves have had far-reaching effects on the anatomy and physiology of vascular plants, resulting in morphological diversity and species expansion. People have long been interested in the question of the nature of the morphology of early leaves and how they were attained. At least five lineages of euphyllophytes can be recognized among the Early Devonian fossil plants (Pragian age, ca. 410 Ma ago) of South China. Their different leaf precursors or “branch-leaf complexes” are believed to foreshadow true megaphylls with different venation patterns and configurations, indicating that multiple origins of megaphylls had occurred by the Early Devonian, much earlier than has previously been recognized. In addition to megaphylls in euphyllophytes, the laminate leaf-like appendages (sporophylls or bracts) occurred independently in several distantly related Early Devonian plant lineages, probably as a response to ecological factors such as high atmospheric CO2 concentrations. This is a typical example of convergent evolution in early plants.

An early origin of secondary growth: Franhueberia gerriennei gen. et sp. nov. from the Lower Devonian of Gaspé (Quebec, Canada)

Secondary xylem (wood) produced by a vascular cambium supports increased plant size and underpins the most successful model of arborescence among tracheophytes. Woody plants established the extensive forest ecosystems that dramatically changed the Earth's biosphere. Secondary growth evolved in several lineages in the Devonian, but only two occurrences have been reported previously from the Early Devonian. The evolutionary history and phylogeny of wood production are poorly understood, and Early Devonian plants are key to illuminating them. A fossil plant preserved anatomically by cellular permineralization in the Lower Devonian (Emsian, ca. 400-395 million years old) Battery Point Formation of Gaspé Bay (Quebec, Canada) is described using the cellulose acetate peel technique. The plant, Franhueberia gerriennei Hoffman et Tomescu gen. et sp. nov., is a basal euphyllophyte with a centrarch protostele and metaxylem tracheids with circular and oval to scalariform bordered multiaperturate pits (P-type tracheids). The outer layers of xylem, consisting of larger-diameter P-type tracheids, exhibit the features diagnostic of secondary xylem: radial files of tracheids, multiplicative divisions, and a combination of axial and radial components. Franhueberia is one of the three oldest euphyllophytes exhibiting secondary growth documented in the Early Devonian. Within the euphyllophyte clade, these plants represent basal lineages that predate the evolution of stem-leaf-root organography and indicate that underlying mechanisms for secondary growth became part of the euphyllophyte developmental toolkit very early in the clade's evolution.

The Middle Devonian plant assemblage from Dechra Aït Abdallah (Central Morocco) revisited

The composition of the allochthonous flora from Dechra Aït Abdallah (Central Morocco), initially described by Termier and Termier (1950), is reassessed from newly collected fossil material. Our work provides an updated taxonomic treatment of the plant remains. The flora comprises two lycophytes (including Leclercqia complexa), the probable iridopterid Anapaulia moodyi, and two aneurophytalean progymnosperms: Rellimia sp. and “Aneurophyton” maroccanum. Our revision confirms the Termiers' main conclusions that this Devonian flora is to date the most diverse and best known from Africa. Based on the complete paleontological evidence available from this locality, a Givetian age is as likely as an Eifelian age for the flora. The abundance of plant remains associated with the extreme scarcity of fertile organs may be accounted for by a taphonomic sorting, climatic conditions and/or specific ecological strategies. The flora of Dechra Aït Abdallah shows similarities with the Middle Devonian floras from the European part of Laurussia. This suggests that the paleogeographical position of Central Morocco permitted exchanges with Laurussia, and infers proximity of the latter with the north-western border of Gondwana during Middle Devonian times.

A new group of Early Devonian plants with valvate sporangia containing sculptured permanent dyads

As part of a study to explore diversity and disparity in Early Devonian terrestrial vegetation, several hundreds of sporangia with in situ spores have been isolated from a Lochkovian locality in Shropshire. These include a small number (seven) of sporangia showing dehiscence into four valves and containing permanent sculptured dyads, belonging to the Cymbohilates horridus complex and C. cymosus, which are recorded in coeval dispersed spore assemblages. A further, previously described, mesofossil comprises an incomplete sporangium containing C. horridus that terminates a naked isotomously branching stem with stomata. The valvate sporangia are placed in a new genus, Partitatheca, containing four species, P. splendida (type), P. horrida, P. densa and P. cymosa, their names reflecting the names of the dispersed spore species and varieties. Complex ultrastructure in the walls of the dyads is similar to that in earlier dyads in the Dyadospora complex where it provides evidence for a hepatic affinity of the earliest embryophytes, but the new taxa present a combination of bryophyte and tracheophyte characters and are considered to represent a new embryophyte lineage. General discussion includes the development of dyads, more particularly their relevance to understanding the diversity in meiotic processes, and the disappearance of dyads from the dispersed spore record prior to the Middle Devonian.

093 Diversity of Late Devonian plants in Australia : contribution of the permineralized assemblage of Barraba, NSW

093 Diversity of Late Devonian plants in Australia : contribution of the permineralized assemblage of Barraba, NSW

Morphology and wall ultrastructure of some Middle Devonian dispersed megaspores from northern Poland

Specimens of dispersed Middle Devonian megaspores have been isolated from core samples from the Miastko 1 borehole in Western Pomerania. Comprehensive investigations using light, scanning and transmission electron microscopy supplement previous information on morphology and gross structure and provide data on spore wall ultrastructure of four megaspore species. Corystisporites acutispinosus is azonate; the inner layer is laminate, and the lumen is lined by a thick, laterally continuous lamina. The outer layer consists of small, tangentially aligned tabular elements that become wider, more extensive and irregularly arranged toward the outside. Coronispora variabilis is a coronate megaspore; the inner layer appears homogenous and is probably lamellate. The outer layer consists of elongate, cylindrical, branching elements that are overlaid within the proximal part of the body by a lamellate, compact, almost homogenous layer. Grandispora ciliata is pseudosaccate. The inner body is laminate with laminae thickening and becoming less continuous and less tightly packed toward the outside. The outermost region of the inner body and the innermost region of the outer envelope consist of tabular and cylindrical elongate units. The bulk of the outer wall is almost homogenous, and near the surface it is granular. Pomeranisporites subtriangularis is pseudozonate. The inner layer appears homogenous except for the presence of a single innermost lamina. The inner part of the outer layer may represent small tabular and cylindrical elements, and the outer part comprises folded laminae. The megaspores studied share numerous features of morphology and wall ultrastructure with the lycopsids, putative lycopsids, and some enigmatic Devonian plants.

A critical account of recent records of Devonian megaflora from the Iberian Peninsula, in geological context

Records of plant megafossils in the Devonian of the Iberian Peninsula refer to sparse drifted remains in marine strata, apart from unidentifiable debris, and misidentified ichnofossils. The age attributions are sometimes questionable. A critical analysis leaves only five localities with incidental Devonian plant megafossils capable of sustaining approximate taxonomic identifications. Another two localities of possible late Devonian age are more likely earliest Carboniferous. The various records are discussed in their geological context, taking into account that the Iberian Massif was constituted from different terranes in Pennsylvanian times. A critical discussion is presented of the reviews published by Montero (2008) and Montero and Diéguez (2010), particularly the latter which adds considerations on floral composition and sedimentary environments which lack a factual basis. A later paper by Cascales-Miñana et al. (2011) is commented on.

A new genus of Early Devonian plants with novel strobilar structures and vegetative appendages from the Posongchong Formation of Yunnan, China

A new plant, Dibracophyton acrovatum gen. et sp. nov., is described from the Lower Devonian (Pragian) Posongchong Formation of Wenshan District, southeastern Yunnan, China. The plant has creeping axes from which arise vegetative and fertile axes. The vegetative axes helically bear lateral dichotomous appendages with curved or round tips. The fertile axes possess terminal strobili with numerous fertile units arranged in irregular helices. Each fertile unit consists of a stalked long-elliptical sporangium, with dehiscence into two equal valves, and two discrete long-ovate bracts covering sporangium from above–below directions. A new genus and species is thus established based on these characters and is temporarily regarded as incertae sedis of Tracheophyta, although it perhaps closes to the barinophytes in affinity. Detailed comparisons with other plants having a similar architecture, i.e., sporangia closely associated with modified vegetative structures, are made. The discovery of D. acrovatum further enriches the composition of the Posongchong flora and demonstrates great morphological disparity of the Early Devonian vascular plants.

A Simple Type of Wood in Two Early Devonian Plants

The advent of wood (secondary xylem) is a major event of the Paleozoic Era, facilitating the evolution of large perennial plants. The first steps of wood evolution are unknown. We describe two small Early Devonian (407 to 397 million years ago) plants with secondary xylem including simple rays. Their wood currently represents the earliest evidence of secondary growth in plants. The small size of the plants and the presence of thick-walled cortical cells confirm that wood early evolution was driven by hydraulic constraints rather than by the necessity of mechanical support for increasing height. The plants described here are most probably precursors of lignophytes.

Lower Devonian plant and spore assemblages from Lower Old Red Sandstone strata of Tredomen Quarry, South Wales

Tredomen Quarry, near Brecon, South Wales, is regarded as a Lower Old Red Sandstone terrestrial lagerstätten and has yielded a palaeobotanical assemblage that illustrates the diversity and possible affinities of early vegetation across the Anglo–Welsh Basin during the lower Lochkovian (Early Devonian). Two boreholes were drilled at the site and subsequent logging resolved the stratigraphic position of the quarry to 64 m above the Bishop's Frome Limestone, thus the lower part of the St. Maughans Formation, a level which few other Anglo–Welsh Basin outcrops expose. A palynological assemblage from the quarry surface is assigned to the lower micrornatus-newportensis Sub-biozone of the lower Lochkovian. The assemblage is diverse, a notable characteristic being ornamented hilate cryptospores of which new species and varieties of Cymbohilates are described ( Cymbohilates horridus var. A, Cymbohilates cymosus var. A–C, Cymbohilates? sp. A–D). Large rhyniophytes and rhyniophytoids including Cooksonia, Salopella and Tarrantia comprise one component of the palaeobotanical assemblage, typical of southern Britain during the Lochkovian. A diverse group of minute axial plants (mesofossils) constitute a second component, rarely found in other assemblages and considered to be synonymous with the exceptionally well-preserved, charcoalified minute sporangia discovered from a mid-Lochkovian locality. Here they provide for the first time evidence that these minute plants were highly branched and are considered to be stem-group embryophytes with both tracheophytic and bryophytic characters, hence a separate component of vegetation living alongside the rhyniophytes and rhyniophytoids. Non-embryophytes form the third component of vegetation and include Nematasketum/Prototaxites and Pachytheca. Minute coalified banded tubes are observed intertwined across bedding planes and are interpreted as hyphae that may have derived from these non-embryophytes.

Discovery of a Lochkovian flora (Lower Devonian) in the Iberian Peninsula

ABSTRACT The Lower Devonian represents an important episode in plant life history, which was marked by the diversification of land plants. Unfortunately, remains of early Devonian plants in the Iberian Peninsula are scarce. In the present paper, we describe a small assemblage of early land plants from the Lochkovian (Lower Devonian) of the Teruel Province in Spain. The main element consists of Taeniocrada-like sterile stems that are predominandy dichotomous and ribbon-like with a narrow central strand. An unidentified fossil formed by dichotomous axes together with an uncertain globular structure were also observed. This finding increases our knowledge of the palaeogeographical distribution of early land plants.

Hydraulics of Asteroxylon mackei, an early Devonian vascular plant, and the early evolution of water transport tissue in terrestrial plants

The core of plant physiology is a set of functional solutions to a tradeoff between CO(2) acquisition and water loss. To provide an important evolutionary perspective on how the earliest land plants met this tradeoff, we constructed a mathematical model (constrained geometrically with measurements of fossils) of the hydraulic resistance of Asteroxylon, an Early Devonian plant. The model results illuminate the water transport physiology of one of the earliest vascular plants. Results show that Asteroxylon's vascular system contains cells with low hydraulic resistances; these resistances are low because cells were covered by scalariform pits, elliptical structures that permit individual cells to have large areas for water to pass from one cell to another. Asteroxylon could move a large amount of water quickly given its large pit areas; however, this would have left these plants particularly vulnerable to damage from excessive evapotranspiration. These results highlight a repeated pattern in plant evolution, wherein the evolution of highly conductive vascular tissue precedes the appearance of adaptations to increase water transport safety. Quantitative insight into the vascular transport of Asteroxylon also allows us to reflect on the quality of CO(2) proxy estimates based on early land plant fossils. Because Asteroxylon's vascular tissue lacked any safety features to prevent permanent damage, it probably used stomatal abundance and behavior to prevent desiccation. If correct, low stomatal frequencies in Asteroxylon reflect the need to limit evapotranspiration, rather than adaptation to high CO(2) concentrations in the atmosphere. More broadly, methods to reveal and understand water transport in extinct plants have a clear use in testing and bolstering fossil plant-based paleoclimate proxies.

Lycopsids from the Upper Devonian of northern Chile with remarks on the geographical distribution of the morphogenus Haplostigma Seward

We here present the first systematic description of Devonian plant fossils from Chile. The material was collected from the Upper Devonian El Toco Formation in the Coastal Cordillera of northern Chile. Plant fossils occur as impressions of lycopsid axes in marine turbiditic greywacke beds and comprise Haplostigmafurquei (Frenguelli) Gutierrez, Malanzania cf. nana Archangelsky, Azcuy and Wagner, and further unidentifiable remains. The biostratigraphic ranges of these taxa agree well with previous age assessments for this sequence, based on conodonts and radiometric data. Haplostigma was widely distributed in the middle-to-high latitude, cool-temperate biome of southern Gondwana, providing further evidence that Middle to Late Devonian extra-tropical floras of Gondwana were dominated by low-diversity associations of herbaceous lycopsids.

Aberlemnia caledonica gen. et comb. nov., a new name for Cooksonia caledonica Edwards 1970

Cooksonia caledonica Edwards 1970 is a small Early Devonian plant, which presents some usual plesiomorphic characters for polysporangiophytes: isotomously branched axes, terminal sporangia. The plant was placed in the genus Cooksonia Lang 1937 on the basis of the “wider than high sporangium” character. The type material has been examined and is re-described. New large specimens, recently found in the Jackson de Figueiredo flora from the Paraná Basin, Brazil, are also studied. The sporangium of C. caledonica is bivalved and possesses a complex subdistal structure for dehiscence. It is different from that of the type species, C. pertoni Lang 1937, which is trumpet-shaped. The morphology of its sporangium clearly excludes the species C. caledonica from the genus Cooksonia. The sporangia of C. caledonica are comparable to those of Sporathylacium salopense Edwards et al. 2001a, which show the same organization. According to the ICBN, conspecificity of the two taxa cannot be established as they do not refer to the same biological structures. A new genus, Aberlemnia, is therefore erected for the plants formerly named C. caledonica.

The invasion of the land by plants: when and where?

The invasion of the land by plants: when and where?

The early land plants from the Armorican Massif: sedimentological and palynological considerations on age and environment

AbstractThe Châteaupanne Unit belongs to the South Armorican domain of the Armorican Massif (France), which is part of the Variscan belt. This unit includes two Lower Devonian plant levels and one of them corresponds to the Basal Member of the Chalonnes Formation. A sedimentological and palaeontological analysis of these fossiliferous deposits from the Châteaupanne quarry (Montjean/Loire, Maine et Loire, France) is presented here for the first time. The age determination based on palynology indicates that the locality records the earliest occurrence of plant megafossils in the Armorican Massif. Their presence suggests an emergence event that has never been described before. Our study highlights the promising potential of the Basal Member of the Chalonnes Formation to aid in understanding these occurrences, and provides new insights into the history of the Variscan belt.