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Premise: The isoetalean lineage has a rich fossil record that extends to the Devonian, but the age of the living clade is unclear. Recent results indicate that it is young, from the Cenozoic, whereas earlier work based on less data from a denser taxon sampling yielded Mesozoic median ages. Methods: We analyzed node ages in Isoetes using two genomic data sets (plastome and nuclear ribosomal cistron), three clock models implemented in MrBayes (ILN, WN, and TK02 models), and a conservative approach to calibration. Results: While topological results were consistently resolved in Isoetes estimated crown group ages range from the latest Paleozoic (mid‐Permian) to the Mesozoic depending on data type and clock model. The oldest estimates were retrieved using the autocorrelated TK02 clock model. An (early) Cenozoic age was only obtained under one specific condition (plastome data analyzed with the uncorrelated ILN clock model). That same plastome data set also yielded the oldest (mid‐Permian) age estimate when analyzed with the autocorrelated TK02 clock model. Adding the highly divergent, recently established sister species Isoetes wormaldii to the data set approximately doubled the average median node depth to the Isoetes crown group. Conclusions: There is no consistent support for a Cenozoic origin of the living clade Isoetes. We obtained seemingly well‐founded, yet strongly deviating results depending on data type and clock model. The single most important future improvement is probably to add calibration points, which requires an improved understanding of the isoetalean fossil record or alternative bases for calibration. [ABSTRACT FROM AUTHOR]

A new lycopsid megaspore species with intricate ornamentation, Flabellisporites zhaotongensis Sui, McLoughlin et Feng sp. nov., is described from the Lopingian Xuanwei Formation of Yunnan Province, Southwest China, using scanning and transmission electron microscopy. This trilete megaspore is characterized by elevated membraneous flanges adorned with multifurcate spines, the longest of which are discrete ribbon-like appendages that basally converge to form a membrane around the equator; and evenly spaced single or bifurcate spines with sharp tips covering the remaining surfaces. Ultrastructural analysis reveals that the megaspore wall consists of four layers: (1) a thin and dense foot layer; (2) an inner spongy layer with small circular or elongate sporopollenin grains with parallel arrangement; (3) an outer, more porous, spongy layer consisting of larger and better interconnected sporopollenin units, that form a grid-like structure in certain cases; and (4) an electron-dense outermost layer forming the sculptural elements. Both morphological and ultrastructural characteristics indicate that the new megaspore species belongs to Isoetales. Our discovery represents the oldest occurrence of Flabellisporites , indicating the origin of this morpho-lineage before the end-Permian mass extinction, and enriches the known diversity of isoetalean lycopsids in the late Permian Cathaysian Flora. • A new lycopsid megaspore species of Flabellisporites is described from the upper Permian of Southwest China. • This is the first record of Flabellisporites from upper Paleozoic strata. • Morphology and ultrastructure indicate the new megaspore species belongs to Isoetales. [ABSTRACT FROM AUTHOR]

Premise of research. Resolving the time and patterns of origination of the Isoetales that thrived in the wet habitats of the late Paleozoic and have extant representatives in the genus Isoetes requires a better understanding of their early members and precursors. Recent studies conducted for a large part in South China acknowledged the diversification of Middle to Late Devonian taxa that possessed isoetalean traits and either were closely related to the Isoetales or occupied a basal position within this plant order. Recent investigations of Late Devonian floras from Australia show that this area, on the northeastern edge of Gondwana, also yields taxa with combinations of characters unknown elsewhere. Methodology. The anatomy and external morphology of an anatomically preserved fragment of a lycopsid axis from the Famennian locality of Barraba, in New South Wales, are described. The new specimen is compared to lycopsid taxa on the basis of anatomically preserved specimens ranging from the Middle Devonian to the Late Carboniferous. Pivotal results. The Barraba specimen shows a new combination of characters consisting of a medullated protostele, three-zoned cortex with a wide middle cortex, homogeneous primary outer cortex, presumably deciduous leaves, and slightly protuberant widely spaced leaf bases. Leaf bases show a single large parichnos and are covered adaxially by a thick translucent layer. The specimen is interpreted as the distal branch of a new arborescent taxon, Lycaugea edieae. Taxa with the closest morphoanatomical characters, such as Wexfordia hookense , belong to the Isoetales and are found in deposits of Europe and the eastern United States. Conclusions. Lycaugea edieae is the third lycopsid taxon described from Barraba, which, to date, has yielded a majority of spore-producing plants. It increases the diversity of the early Isoetales around the Devonian-Carboniferous boundary. The Barraba flora is more similar to the contemporaneous flora in southern Laurussia than to that in China. [ABSTRACT FROM AUTHOR]

Isoetes are ancient quillworts members of the only genus of the order Isoetales. The genus is slow evolving but is resilient, and widespread worldwide. Two recently described species occur in the Eastern Brazilian Amazon, Isoetes serracarajensis and Isoetes cangae. They are found in the ironstone grasslands known as Canga. While I. serracarajensis is present mostly in seasonal water bodies, I. cangae is known to occur in a single permanent lake at the South mountain range. In this work, we undertake an extensive morphological, physiological and genetic characterization of both species to establish species boundaries and better understand the morphological and genetic features of these two species. Our results indicate that the morphological differentiation of the species is subtle and requires a quantitative assessment of morphological elements of the megaspore for diagnosis. We did not detect differences in microspore output, but morphological peculiarities may establish a reproductive barrier. Additionally, genetic analysis using DNA barcodes and whole chloroplast genomes indicate that although the plants are genetically very similar both approaches provide diagnostic characters. There was no indication of population structuring I. serracarajensis. These results set the basis for a deeper understanding of the evolution of the Isoetes genus. [ABSTRACT FROM AUTHOR]

Two distinctive lycopsid megaspore species, Henrisporites yunnanensis Sui, McLoughlin et Feng sp. nov. and H. qujingensis Sui, McLoughlin et Feng sp. nov., are described from the Lopingian Xuanwei Formation of Yunnan Province, Southwest China, using scanning and transmission electron microscopy. Henrisporites yunnanensis is characterized by prominent membranous triradiate labra with ragged margins, a broad irregularly serrated membranous zona with radiating spiny extensions, and ramified or unbranched spines on the spore surface, those on the distal surface especially having capillate termini. Punctatisporites -type microspores occur adhering to the megaspore surface. The megaspore wall incorporates four layers, viz., from inside to outside: (1) a thin and dense foot layer especially thickened at the laesurae lips; (2) a moderately-thick layer with small circular and loosely distributed sporopollenin grains with parallel arrangement; (3) a thick spongy layer consisting of elongate, curved and interconnected sporopollenin units perpendicular to the inner layers; and (4) an electron-dense outermost layer forming the ornamentation. Henrisporites qujingensis has lower membranous labra, a generally continuous membranous zona with radiate spiny margins but, in some cases, dissected into single fimbria, and bearing sparsely distributed and locally forked stubby spines over the spore surface. Henrisporites qujingensis also has a four-layered wall. The innermost thin foot layer is covered by a loose layer of tiny parallel sporopollenin grains. A thick spongy layer is developed exterior to the second layer and comprises elongate, curved, and intersecting sporopollenin units forming a porous zone. The outermost layer consists of varied sculptural processes with contrasting densities between the proximal and distal surfaces. The morphological and ultrastructural characteristics suggest that these new megaspores belong to Isoetales. Our discovery represents the earliest global occurrence of Henrisporites , which has been documented exclusively from the Mesozoic in previous studies. • Two new lycopsid megaspore species of Henrisporites are described from the Permian of Southwest China. • These are the first records of Henrisporites from upper Paleozoic strata. • Henrisporites yunnanensis is associated with Punctatisporites microspores. • Morphology and ultrastructure indicate the two new megaspores belong to Isoetales. [ABSTRACT FROM AUTHOR]

The paucity of late Paleogene and Neogene floras from Antarctica limits our ability to understand the interplay between Antarctic climate evolution and the impact that glaciation had on the vegetation, in particular, how the vegetation changed from temperate Eocene forests, to today’s sparse vegetation. Fluvial and lacustrine strata deposited in a wet-based glacial sequence (Friis Hills, McMurdo Dry Valley sector, Transantarctic Mountains) have yielded abundant megaspores. These strata are early Miocene based on correlation with a volcanic ash dated at 19.76 ± 0.11 Ma. The megaspores are up to 736 µm in diameter with well-developed wing-like laesurae and equatorial zona. The morphology is consistent with extantIsoetes, and demonstrates the presence of Lycopsida and the Isoetaceae within Antarctic Miocene floras. Today,Isoetesis widespread from the Tropics to the Arctic such as Greenland (I. echinospora, I. lacustris) and from marginal marine (I. ekmanii) to high altitudinal environments (I. lechleri), though commonly associated with lacustrine or aquatic environments. The fossil spores occur in fluvial and lacustrine beds, suggesting the parent plants were aquatics. The occurrence together with mosses andNothofagusleaves points to persistent vegetation in the early Miocene of Antarctica. [ABSTRACT FROM PUBLISHER]

The monotypic Azaniadendron fertile Rayner, a lycopsid from the Guadalupian of Gondwana, is investigated providing new data on the morphology of its leaf cushions and their variation in shape. Evidence for a ligule is presented for the first time, elucidating, at least for this genus, a dilemma about the presence of this structure in lycopsids from the Permian Glossopteris flora. New data on its fertile axes question the assumption that the taxon produced true cones. We hypothesise that the genus belong to the Isoetales. Unequivocal evidence of the taxon is so far known only from the South African Vryheid Formation and its equivalent beds. • The monotypic lycopsid genus Azaniadendron Rayner is revisited. • Shape variations of its leaf cushions are described in detail. • Evidence of ligule is described for the first time. • It is hypothesised that the genus has affinities with the Isoëtales. [ABSTRACT FROM AUTHOR]

Lycophytes were an important group of plants in the late Permian (Lopingian) vegetation of Southwest China. However, our understanding of these lycophytes is based mostly on the study of megafossil specimens. Here, we describe a unique lycophyte megaspore, Paxillitriletes permicus Sui, McLoughlin et Feng sp. nov., from the Lopingian Xuanwei Formation of Yunnan Province, Southwest China. This trilete megaspore is characterized by prominent membraneous triradiate flanges, long bifurcate spines, an arcuate ridge expanded into a zona, and triangular to polygonal reticulate sculpture. Ultrastructural analysis reveals that the megaspore wall consists of four layers. The innermost layer is the foot layer, which forms a thin and solid basal lamina. It is covered by a dense layer containing small and parallel sporopollenin grains. A thick spongy layer is developed exterior to the dense layer and consists of elongate, curved, and intersected sporopollenin units with porous zones. The outermost layer is dense, of variable thickness, and forms the processes. Morphological and ultrastructural features indicate that the new megaspore belongs to a herbaceous isoetalean. This is the first detailed investigation of megaspores from the Lopingian of China using scanning and transmission electron microscopy. Our discovery represents the oldest occurrence of Paxillitriletes , and adds to the diversity of late Permian lycophytes in the Cathaysian Flora in the paleotropics of the eastern Tethys Ocean. • A new lycophyte megaspore species is described from the Lopingian of Southwest China. • The megaspore has membraneous triradiate flanges, bifurcate spines, narrow zona, reticula. • Its wall has a dense layer with small and parallel sporopollenin grains enclosing foot layer. • A thick porous layer with elongate, curved sporopollenin units exterior to the dense layer. • Morphology and ultrastructure indicate the megaspore belongs to a herbaceous isoetalean. [ABSTRACT FROM AUTHOR]

Impression fossils of a cormose rhizomorph are described from the Givetian (late Middle Devonian) Hujiersite Formation, Hoxtolgay, West Junggar, Xinjiang, Northwest China. The rhizomorph is bulbous, with densely arranged, oval rootlet bases enclosing orbicular vascular bundle scars, exhibiting considerable resemblance to that of the Late Devonian–Carboniferous rhizomorphic lycopsid of Isoetales sensu stricto . The present specimens may represent the earliest cormose lycopsid rhizomorph. Their implications for the origin and early evolution of rhizomorphic lycopsids are discussed. [ABSTRACT FROM AUTHOR]

Diminutive, silica-permineralized lycopsid axes, from a Guadalupian (Middle Permian) silicified peat in the Bainmedart Coal Measures of East Antarctica are described and assigned to Paurodendron stellatum sp. nov. Axes consist only of primary-growth tissues with a vascular system characterized by an exarch actinostele with 6–20 protoxylem points. Stems have a relatively narrow cortex of thin-walled cells that are commonly degraded, but the root cortex typically contains more robust, thick-walled cells. The stems bear helically inserted, elliptical–rhombic, ligulate microphylls. Roots possess an eccentrically positioned monarch vascular strand. Paurodendron stellatum is one of a very small number of anatomically preserved lycopsid axes described from the Gondwanan Permian and represents the first post-Carboniferous record of this genus. Based on dispersed vegetative remains, megaspores and microspores, herbaceous lycopsids, such as P. stellatum , appear to have been important understorey components of both low- and high-latitude mire forests of the late Palaeozoic. [ABSTRACT FROM AUTHOR]

A lycopsid reproductive organ from the Koipato Group in the southern Humboldt Range, Nevada, is described. It was found in fine-grained volcanogenic turbitides of mid-Spathian age derived from the Koipato volcanic arc. The strobilus is preserved as an imprint with small amounts of organic material. The shape of the reproductive organ, as well as the sporophylls, resemble those of the genus Pleuromeia , especially Pleuromeia sternbergii. Immature spores extracted from the organic matter are partly covered by authigenic muscovite crystals. This is the first record of this iconic taxon in the Early Triassic of North America. It further strengthens the global distribution of this genus during the Early Triassic by filling up a major paleogeographic gap. • First Lower Triassic Pleuromeia strobilus from the USA is described. • In situ spores seem to be immature. • Macrofossils indicate Pleuromeia heyday during late Early to early Middle Triassic. [ABSTRACT FROM AUTHOR]

Late Devonian Minostrobus chaohuensis is one of the earliest monosporangiate-strobilate isoetaleans. Based on new material of this plant, the vegetative axis and microsporangiate strobilus are studied in detail, and the whole plant knowledge is summarized. The vegetative axis is isotomously branched. The stem is up to 55 mm in diameter with helically arranged leaf cushions. Stems and thick branches bear long fusiform leaf cushions and interareas with vertical linear ornamentations. A ligule pit, oblanceolate leaf scar, and vascular bundle scar appear on the leaf cushion. Distal axes have persistent lanceolate leaves and rhombic leaf bases. The microsporangiate strobilus is cylindrical in shape, possesses sporophyll with alate pedicel and long triangular lamina, uniseriate sporangial wall, subarchesporial pad inside the sporangium, and microspore with cingulum. Based on comparisons with other isoetaleans, the usage of the terms “leaf cushion” and “leaf base” is discussed, and Minostrobus chaohuensis is considered as a tree-like lycopsid. It suggests that arborescent isoetaleans with monosporangiate strobili had appeared and diversified in the Late Devonian. The multi-dichotomous branching system of Minostrobus provides new data on the evolution of growth architecture in rhizomorphic lycopsids. [ABSTRACT FROM AUTHOR]

In this paper well-preserved isoetalean microsporophyll, containing in situ microspores, is described from the uppermost part of the Utrillas Formation (latest Albian) in Teruel Province, northeastern Spain. Similar but dispersed microspores were described previously as Peromonolites. Fossil plant impressions and compressions including the sporophyll lamina and micro sporangium are referred to the fossil genus Isoetites. Although Isoetes-like megafossil remains, often with in situ or associated megaspores, are known from quite a few Cretaceous sites, and dispersed microspores are known, the presence of intact microsporangia is rare. Herein we suggest that microsporangia may have dispersed in masses, possibly representing a new unknown strategy in microspore dispersal in this group of plants. [ABSTRACT FROM AUTHOR]

Here, we describe and illustrate by transmitted light and scanning electron microscopy the first Australian Jurassic megaspore assemblages. The megaspores and other mesofossils were isolated from terrestrial deposits of the Marburg Subgroup (late Pliensbachian) at Inverleigh Quarry, Clarence-Moreton Basin, eastern Australia. Nine megaspore taxa are identified including one new species:Paxillitriletes rainei. Miospore assemblages recovered from the same samples at Inverleigh reveal a slightly higher diversity of lycophyte microspores. The collective megaspore suite from Inverleigh shares several genera with mid-Mesozoic assemblages from widely distributed parts of the world, but most of the Inverleigh species have subtle morphological differences from congeneric forms elsewhere. The megaspores accumulated in fluvial floodplain facies and are associated with mostly dissociated isoetalean leaf debris. Other mesofossils in the sampled interval include annelid egg cases, dispersed seeds and charcoal. Invertebrate burrows and possible vertebrate tracks also occur in this succession. Lycophyte macrofossils are otherwise known from only two other Australian Jurassic deposits. The richness of the megaspore and microspore suites attest to a significant diversity of lycophytes in the Australian Jurassic floras not hitherto appreciated from described macrofloras. [ABSTRACT FROM PUBLISHER]

To investigate the phylogeny of early lycopsids, cladistic analyses using both parsimony and Bayesian approaches are presented, with a data matrix of 33 morphological characters across 25 taxa. The resulting parsimony and Bayesian trees showed overall similarities in tree topologies. In the Bayesian tree, the Protolepidodendrales and the heterosporous lycopsids are recognized as two monophyletic groups, and within the latter group, the Isoetales sensu lato forms a subclade. This topology implies that the acquisition of a ligulate character evolved twice in the lycopsids, once in the protolepidodendralean Leclercqia Banks et al., and once in the heterosporous lycopsid clade. Phylogenetic positions of several lycopsid plants previously reported from the Mid-Upper Devonian of South China, which have uncertain ordinal affinities, were estimated by the cladistic analyses; cf. Longostachys Xue et Hao, Longostachys Zhu et al., Monilistrobus Wang et Berry, and Yuguangia Hao et al. fall well within the Isoetales clade, as earliest members of this order, while Minostrobus Wang and Wuxia Berry et al. are nested within the basal part of the heterosporous lycopsids. Bayesian analyses are a very useful approach in systematic studies and can be applied in analyzing paleobotanical data sets as well. [ABSTRACT FROM AUTHOR]

Abstract: A large assemblage of stems, leaves and reproductive structures collected from a single horizon in the Lower Mississippian (Lower Carboniferous) Price Formation of southwestern Virginia, USA is recognized as representing the components of a distinctive arborescent lycopsid. While similar forms previously were included in Lepidodendropsis Lutz, an eligulate lycopsid in which leaf scars are not apparent, these specimens document the presence of both well-defined leaf scars and ligules. Among larger specimens, leaf base patterns change along the length of a single stem, each morphology conforming to a different species of Lepidodendropsis. Because of the overlapping variability within specimens, we find that stems of different sizes and leaf base patterns are parts of the same plant. This plant was a tree with a trunk that probably attached to a cormose base previously recognized as Protostigmaria Jennings. The trunk extended 3–4m before branching dichotomously to produce a crown of several orders of branches, with the distal-most ones still bearing long tapering leaves. Sporangia are borne in fertile zones; the plant is heterosporous. The presence of leaf scars and a ligule (features explicitly lacking in the generic diagnosis of Lepidodendropsis) as well as other plant organs for this taxon precludes inclusion in Lepidodendropsis; rather, this plant should be placed in a new genus. A better understanding of this plant, and other specimens attributed to Lepidodendropsis, may aid in elucidating transitions and phylogenetic relationships among Late Devonian–Late Carboniferous arborescent lycopsids. [ABSTRACT FROM AUTHOR]

[Display omitted] • Plastome-based phylogenetic reconstructions revealed well-supported nodes. • Several incongruencies between plastome and rDNA-based phylogenies were found. • Chromosome counts identified three diploids, five tetraploids and one likely hexaploid. • The radiation of the TAA clade occurred in the Pleistocene at 1.7 Ma. • The TAA clade evolved first in the dry area before reaching more humid regions. The genus Isoëtes is globally distributed. Within the Neotropics, Isoëtes occurs in various habitats and ecosystems, making it an interesting case study to address phylogenetic and biogeographic questions. We sequenced and assembled plastomes and ribosomal DNA (rDNA) sequences to reconstruct phylogenetic relationships in Isoëtes from tropical regions in the Neotropics. The ploidy level of nine taxa was established to address the potential source of phylogenetic incongruence in the genus. Node ages were estimated using MCMCTree. The ancestral range estimates were conducted in BioGeoBEARS. Plastome-based phylogenies were congruent throughout distinct matrices and partition schemes, exhibiting high support for almost all nodes. Whereas, we found incongruences between the rDNA and plastome datasets. Chromosome counts identified three diploids, five tetraploids and one likely hexaploid among Neotropical species. Plastome-based node age estimates showed that the radiation of the crown Isoëtes group occurred at 20 Ma, with the diversification of the tropical American (TAA) clade taking place in the Pleistocene at 1.7 Ma. Ancestral range estimates showed that the ancestor of the TAA clade may have evolved first in the dry diagonal area in South America before reaching more humid regions. In addition, the colonization of the Brazilian semiarid region occurred three times, while the occupation of the Cerrado and Amazon regions occurred twice and once, respectively. Our study showed a large unobserved diversity within the genus in warm-dry regions in the Neotropics. Plastomes provided sufficient genomic information to establish a robust phylogenetic framework to answer evolutionary questions in Isoëtes from the Neotropics. [ABSTRACT FROM AUTHOR]

The article presents an in-depth discussion of the morphological and anatomical variation in sporophylls across and within three populations of Isoetes sinensis in China. Isoetes sinensis is an aquatic fern confined to clear waters. This wild plant is considered rare and endangered as it decreased in numbers and even disappeared from several locations in China.

The microspores of Isoetes escondidensis, I. gardneriana, I. herzogii, I. pedersenii, and I. savatieri were analyzed with transmission and scanning electron microscopy. The selected species were found to be representative of the diversity found in 24 taxa previously studied that grow in southern South America. The sporoderm is similar in the five types and is composed, from the outside to the inside, of perispore, para-exospore, exospore, and endospore. In I. escondidensis, I. gardneriana, I. herzogii, and I. savatieri, the perispore is lacunose, whereas in I. pedersenii, it is camerate. The para-exospore is formed of large superimposed and fused bars, which are more numerous and thicker in immature spores. The exospore shows uniform characteristics and a strongly contrasted cover. It has pluristratified zones on both sides of the aperture. The presence of radial rodlets between the para-exospore and exospore and in the supra-apertural chamber is described here for the first time. The endospore has a fibrillate or reticulate structure, or both structures may be present. A boundary within the fibrillate endospore is evident, which might be related to stages of deposition. The surface characteristics are formed by either the middle and outer strata of the perispore or elements on the outer surface, as in I. escondidensis. The characteristics of the microspore surface and of the perispore structure provide characteristics useful for systematic purposes at the infrageneric level. [ABSTRACT FROM AUTHOR]

The article reports on the results of a study of the phylogenetic root of the lycopsid genus, Isoëtes. The study examined the characteristics of the early branching patterns within Isoëtes using an expanded set of taxa and three molecular markers. It also assessed the saturation in the molecular data sets, tested for differences in evolutionary rate, determined the stability of the ingroup topology and evaluated the applicability of the molecular clock.

New collections of pyritized axes of the lycophyte Wexfordia hookense have been made from the Upper Devonian (uppermost Famennian) type locality at Sandeel Bay, County Wexford, in south-eastern Ireland. The specimens reveal additional histological features that permit reinterpretation of the morphology of this taxon and reevaluation of its taxonomic affinities. Wexfordia is shown to possess both secondary xylem, with narrow, uni- to biseriate rays, and periderm. The range of variation in relative amounts of primary and secondary xylem can be correlated with position in the mature plant. This evidence indicates that Wexfordia was a small tree rather than an herbaceous form. Fine structure of tracheids and additional anatomical features strongly support affinities with Carboniferous arborescent Isoetales, rather than Devonian Protolepidodendrales, and further support the hypothesis that radiation in this lineage was well underway prior to the Carboniferous. © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 144 , 275–287. [ABSTRACT FROM AUTHOR]