The origin and early evolution of land plants in the mid-Palaeozoic era, between about 480 and 360 million years ago, was an important event in the history of life, with far-reaching consequences for the evolution of terrestrial organisms and global environments. A recent surge of interest, catalysed by palaeobotanical discoveries and advances in the systematics of living plants, provides a revised perspective on the evolution of early land plants and suggests new directions for future research.

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The origin and early evolution of plants on land

Reconstructing the origin and evolution of land plants and their algal relatives is a fundamental problem in plant phylogenetics, and is essential for understanding how critical adaptations arose, including the embryo, vascular tissue, seeds, and flowers. Despite advances in molecular systematics, some hypotheses of relationships remain weakly resolved. Inferring deep phylogenies with bouts of rapid diversification can be problematic; however, genome-scale data should significantly increase the number of informative characters for analyses. Recent phylogenomic reconstructions focused on the major divergences of plants have resulted in promising but inconsistent results. One limitation is sparse taxon sampling, likely resulting from the difficulty and cost of data generation. To address this limitation, transcriptome data for 92 streptophyte taxa were generated and analyzed along with 11 published plant genome sequences. Phylogenetic reconstructions were conducted using up to 852 nuclear genes and 1,701,170 aligned sites. Sixty-nine analyses were performed to test the robustness of phylogenetic inferences to permutations of the data matrix or to phylogenetic method, including supermatrix, supertree, and coalescent-based approaches, maximum-likelihood and Bayesian methods, partitioned and unpartitioned analyses, and amino acid versus DNA alignments. Among other results, we find robust support for a sister-group relationship between land plants and one group of streptophyte green algae, the Zygnematophyceae. Strong and robust support for a clade comprising liverworts and mosses is inconsistent with a widely accepted view of early land plant evolution, and suggests that phylogenetic hypotheses used to understand the evolution of fundamental plant traits should be reevaluated.

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Phylotranscriptomic analysis of the origin and early diversification of land plants

http://www.noahwhiteman.org/uploads/7/1/3/1/7131048/trplsc952.pdf

Evolution of jasmonate and salicylate signal crosstalk.

Although macroscopic plants, animals, and fungi are the most familiar eukaryotes, the bulk of eukaryotic diversity is microbial. Elucidating the timing of diversification among the more than 70 lineages is key to understanding the evolution of eukaryotes. Here, we use taxon-rich multigene data combined with diverse fossils and a relaxed molecular clock framework to estimate the timing of the last common ancestor of extant eukaryotes and the divergence of major clades. Overall, these analyses suggest that the last common ancestor lived between 1866 and 1679 Ma, consistent with the earliest microfossils interpreted with confidence as eukaryotic. During this interval, the Earth's surface differed markedly from today; for example, the oceans were incompletely ventilated, with ferruginous and, after about 1800 Ma, sulfidic water masses commonly lying beneath moderately oxygenated surface waters. Our time estimates also indicate that the major clades of eukaryotes diverged before 1000 Ma, with most or all probably diverging before 1200 Ma. Fossils, however, suggest that diversity within major extant clades expanded later, beginning about 800 Ma, when the oceans began their transition to a more modern chemical state. In combination, paleontological and molecular approaches indicate that long stems preceded diversification in the major eukaryotic lineages.

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Estimating the timing of early eukaryotic diversification with multigene molecular clocks

The East African rift system

The terrestrialization process: A palaeobotanical and palynological perspective

Urpicalis steemansii gen. et sp. nov. is described from the Lower Devonian (early Emsian) of Fooz-Wepion (northern margin of Dinant Synclinorium, Belgium). About twenty specimens are known. They are tiny sporangiferous axis systems, isotomously branched and devoid of enations. One of these axis systems is probably borne on a wider smooth axis. The sporangia are fusiform to oval-elongated. One of them is often placed at the axil of the isotomy, while the others are inserted on the adaxial side of the isotomous axes. The sporangia are parallel to the bisector of the isotomy. Plant anatomy and spores are unknown. This insertae sedis new taxon recalls the fertile axes of aneurophyton and may represent one of the first steps leading to the Progymnosperms

Les plantes emsiennes de Fooz-Wépion (bord nord du Synclinorium de Dinant, Belgique). II: Urpicalis steemansii gen. et sp. nov.

1. Introduction and geological context In Belgium, Famennian rocks crop out extensively across the Dinant Synclinorium (allochtonous), Haine-Sambre-Meuse Overturned Thrust Sheets (former southern limb of the Namur Synclinorium; see Belanger et al., 2012, for discussion about this Variscan structural element), Vesdre area (lateral equivalent to the latter), Theux Tectonic Window (autochtonous) and Brabant Parautochton (former northern limb of the Namur Synclinorium, parautochtonous). The Famennian shows a regressive trend from open marine shales of the Famenne Group (lower Famennian) to fluvio-lagunal siltstones, sandstones and dolomites of the Upper Famennian Evieux Formation (Thorez & Dreesen, 1986). The litho- and biostratigraphy of the stage are well known, thanks to the seminal works of Thorez and colleagues (Thorez et al., 1977; Thorez & Dreesen, 1986, 2002; Thorez et al., 2006), which were mainly dedicated to the Condroz area (eastern Dinant Synclinorium). The Famennian lithostratigraphy of the Haine-Sambre-Meuse Overturned Thrust Sheet (sensu Belanger et al., 2012), Vesdre area and Theux Tectonic Window, even if similar, remains relatively poorly known. In comparison to contemporaneous deposits exposed in the Dinant Synclinorium, the Upper Famennian deposits known from these Variscan structural units are more proximal and the fluvial and lagunal facies are commonly more developed (Thorez et al., 1988). This paper describes a recently discovered Upper Famennian locality

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Flora and fauna from a new Famennian (Upper Devonian) locality at Becco, eastern Belgium

Tree growth, including radial growth, is controlled by a complicated combination of climate-related factors. In seasonal climates many species of trees form clearly defined annual growth rings. Quantitative and qualitative analyses of growth rings are high resolution proxies of ancient environments, thus facilitating studies of past climates. We have applied this method to growth rings of early Cretaceous softwood branches from the Wealden facies of the Mons Basin, Belgium. Preliminary results confirm that during the early Cretaceous, the Mons Basin was located at 30-35°N, presumably in a tropical climate, with a succession of marked dry and wet seasons (Koeppen's climate type Aw). The Mean Sensitivity coefficient (the difference in a sequence of rings of the widths of consecutive ring pairs /average ring width) is high (above 0.4), and indicates unstable palaeoenvironmental conditions.

https://hal.archives-ouvertes.fr/hal-00168235/document

Quelques implications paléoclimatiques de l'observation de bois fossiles du Wealdien du bassin de Mons (Belgique) - Résultats préliminaires.

Most evolutionary innovations in plant vascular tissues, including secondary growth, occurred during the Devonian period (~420 to 360 million years ago). Such innovations had a major impact on land colonisation by plants and on their biodiversity. Here, we show the hydraulic conductance of the secondary xylem of three shrubby or arborescent plant fossils (a probably new genus of Cladoxylopsida, the archaeopteridalean genus Callixylon and the stenokolean genus Brabantophyton). Evidences come from the Ronquières fossil site (Belgium). This site is considered mid-late Givetian/earliest Frasnian in age. Results reveal that hydraulic conductivity of these early woody plants is more or less similar to that of modern gymnosperms, meaning that water transport was already as efficient in Devonian plants as it is in living plants. Our results further suggest that tracheids with features helping for optimised water transport were quickly selected in the evolutionary history of vascular plants.

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Philippe Gerrienne

Papers

The terrestrialization process: A palaeobotanical and palynological perspective

Les plantes emsiennes de Fooz-Wépion (bord nord du Synclinorium de Dinant, Belgique). II: Urpicalis steemansii gen. et sp. nov.

Flora and fauna from a new Famennian (Upper Devonian) locality at Becco, eastern Belgium

Quelques implications paléoclimatiques de l'observation de bois fossiles du Wealdien du bassin de Mons (Belgique) - Résultats préliminaires.

On the hydraulic conductance of three woody Devonian plants