Foerstia and recent interpretations of early, vascular land plants

Schopf, James M. 1978 04 15: Foerstia and recent interpretations of early, vascular land plants
Foerstia should be regarded as a marine fucoid, contrary to the recent interpretation of Gray and Boucot who relate these fossils to land plants. Although the megaspore coats are resistant and may be waxy, the thallus lacks cuticle and it has internal filamentous tissue like Fucus and other fucoidal algae. The megaspores, borne in fucoidal conceptacles, are unusual and may be forerunners of the more reduced oocytes that occur in modern Fucales. Detailed illustrations are provided. There is no evidence that these plants have ever been anything but marine. Likewise, tubular microfossils that show internal thickenings and occur in Ordovician and Silurian marine deposits should not be designated 'tracheid-like', as done by Gray and Boucot, because it is unlikely they represent land plants or function in conduction. They show a surprisingly consistent association with Chitinozoa. They illustrate the adage that structures identified simply by their form may be of diverse origin. Neither Foersria nor the annulate tubules are relevant to the origin of temestrial vegetation.     

The Devonian land plant Protosalvinia

Gray, Jane&Boucot, ArthurJ. 197901 15: The Devonian land plant Protosalvinia. Lethaia . Vol. 12, pp. 57–63. Oslo. ISSN 0024–1164.
Protosalvinia (=Foerstia ) shows a number of morphological features which suggest that it was a land plant, possibly an emergent aquatic. Certain kinds of biochemical data, as presently interpreted, also support the morphological evidence. The weight of evidence supports neither a fucoid nor even an algal attribution for this enigmatic plant. Protosalvinia should be treated as the representative of a separate group of land plants, as previously advocated. Tracheid-like tubes with internal spiral thickenings appear on the basis of direct comparison to be morphologically identical to those of nematophytalean origin. They may have functioned in a capacity similar to the tracheids of vascular plants. The Nematophytales are non-marine plants of uncertain taxonomic position.     

Anatomy and Morphology of Pinnatiramosus,a New Plant from the Middle Silurian (Wenlockian) of China

A new genus and species Pinnatiramosus qianensis is described from the Xiushan Formation of Middle Silurian (Wenlockian)in the north of Guizhou, China. This plant consists of a prostrate axis and erect pinnate branching system. Conductin gbundle is comprised of tubular cells with scalariform or alternate simple pits. Pinnatiramosus gen. nov. Diagnosis: Plant cylindrical, differentiated into erect branches and prostrate axes; erect branches much branched, consisting of regular or irregular pinnate lateral branches; laterals opposite or alternate, with basal parts constricted and acute or blunt apices. Conducting bundle comprised of longitudinally aligned tubes with secondary thickening. Reproductive structures nor seen. Derivation of name: Pinnatus (Latin)=pinnate and ramosus (Latin)=ramose, referred to the external morphology of the plant. Pinnatiramosus qianensis sp. nov. Diagnosis: Characters described as the genus. Prostrate axes at least 400 mm in length and 3–6 mm in diameter, produced erect longer branches and downward shorter branches; erect branches up to 200 mm long and vary from 1.0 to 2.5mm in diameter, branched at least six orders, with lateral branches unequally developed, long laterals scattered among short ones; lateral branches oppositely or alternately arranged on main axis, 1–3 mm: apart; ultimate bran- ches 0.4–0.8 mm in diameter, with acute or blunt apex; borne at angles of 40–70˚ with main axis. Conducting bundle ca. 1/4 of the axis diameter, composed of tubular elements with secondary thickening; tubes range from 15–54μm in diameter, with blunt end wall; secondary wall averages 4.86 μm in thickness, ranging 2.5–6.6 μm, with scalariform and alternate pits. Derivation of name: Qian is the abbreviation for Guizhou province from where the plants are found. In this paper, is made the comparison of this new plant with fossil and living algae as well as early vascular plants on the basis of its external morphology and internal structure According to the comparison, Pinnatiramosus belongs to one of specialized plants with tracheophyte- like conducting tissue. Some interesting opinions are here provided as follows: (i) Silurian is, an important age of plant evolution. During this period certainly coexist not only various algae and undoubted vascular plants but also a group of interesting plants that were just immigrating from aquatic to terrestrial environments. (ii) The transmigration of algae from water to land occurred along several different evolutionary lines. Accompanying changes of these algae on morphology and anatomy were adapted to terrestrial environments. (iii) Pinnatiramosus represents a group of new plants with remarkably nontracheophyte morphology but tracheophyte- like anatomy. (iv) The tracheid-like tubes, macerated out of Silurian rocks, derived more probably from non-vascular plants such as Pinnatiramosus, Prototaxitesor Nematothallus than from vascular plants.     

Early vascular land plants: proof and conjecture

Megafossil evidence does not fill the 'evolutionary gap' between land plants and their hypothetical green algal ancestors. Rare Late Silurian vascular plant megafossils provide little information about the morphological, physiological, biochemical, and ecological steps that preceded their evolution. Dissociated trilete spores, spore tetrads, cuticle- and tracheid-like structures far exceed the abundance and diversity of Silurian vascular plant megafossils, and appear millions of years before them. In reference to whole-bodied organisms, these or analogous structures belong to land plants or emergent aquatics; they may represent plants evolutionarily intermediate between green algae and descendent vascular plants at the bryophyte or pre-bryophyte stages. Changes in the cellular biochemistry of pre-Devonian land plants in response to the selective pressures of terrestrial life may have led to the origin of lignin and cutin, neither of which has any counterpart among the algae, and to the evolutionary surge of the vascular plants in the Early Devonian represented by the plant megafossil record. Positive correlation between abundance and diversity of trilete spores and shallow-water, nearshore sites reinforces conclusions based on morphology that a terrestrial flora existed well prior to the appearance of vascular plant megafossils.     

The microfossil record of early land plants

Dispersed microfossils (spores and phytodebris) provide the earliest evidence for land plants. They are first reported from the Llanvirn (Mid-Ordovician). More or less identical assemblages occur from the Llanvirn (Mid-Ordovician) to the late Llandovery (Early Silurian), suggesting a period of relative stasis some 40 Myr in duration. Various lines of evidence suggest that these early dispersed microfossils derive from parent plants that were bryophyte-like if not in fact bryophytes. In the late Llandovery (late Early Silurian) there was a major change in the nature of dispersed spore assemblages as the separated products of dyads (hilate monads) and tetrads (trilete spores) became relatively abundant. The inception of trilete spores probably represents the appearance of vascular plants or their immediate progenitors. A little later in time, in the Wenlock (early Late Silurian), the earliest unequivocal land plant megafossils occur. They are represented by rhyniophytoids. It is only from the Late Silurian onwards that the microfossil/ megafossil record can be integrated and utilized in interpretation of the flora. Dispersed microfossils are preserved in vast numbers, in a variety of environments, and have a reasonable spatial and temporal fossil record. The fossil record of plant megafossils by comparison is poor and biased, with only a dozen or so known pre-Devonian assemblages. In this paper, the early land plant microfossil record, and its interpretation, are reviewed. New discoveries, novel techniques and fresh lines of inquiry are outlined and discussed.     

Histological study of callus formation and root regeneration from mung bean (Vigna radiata W.)

We have established a reproducible culture system for callus formation and root development from juvenile stem segments of mung bean(Vigna radiata). In particular, we have studied the influence of plant growth regulators. Induction of calli from young stem explants was very effective on MS inorganic salts supplemented with 0.5 mg/L 2,4-D and 1.0 mg/L kinetin. In regenerating adventitious roots from callus tissues, we found that a combination of 0.75 mg/L NAA, 1.5 mg/L kinetin, and MS salts resulted in 20% efficiency. Histological examination showed that callus tissues originated from out-growths of the cambium rings through de-novo meristematic activity. Those rings were localized outside the vascular cambium. Adventitious roots that developed from root primordia originated from the center of the Callus masses. These primordia produced tracheid-like cells, which then became meristemoid cells for the cambium. Newly formed adventitious roots had the typical tetrarche actinostele type.     

Biogeography of the changing Phanerozoic world

Practically each one of the chapters in the book Historical Biogeography, Plate Tectonics, and the Changing Environment (Gray & Boucot 1979) would have deserved to be channelled to readers in the form of articles in periodicals, to be efficiently circulated among the most concerned specialists as offprints and to be abstracted and indexed by the secondary information services.     

Graptolites from glacial erratics of the Laerheide area,northern Germany

Ordovician and Silurian glacial erratics of the Laerheide area (Lower Saxony, north-western Germany) bear well-preserved graptolites. The faunas provide important information on the origin and transport direction of the sediments preserved in a kame, representing the Drenthe stadial of the Saalian glaciation. The faunas even include species not commonly encountered in the successions of mainland Sweden, from where the erratics presumably originated. The most common graptolites are from Upper Ordovician (Sandbian to Katian) limestones and from Katian black shales. More common, however, are greenish limestones, sand- and siltstones, often combined in the term ‘Grünlich-Graues Graptolithengestein’, in which upper Wenlock to Ludlow (upper Silurian) graptolites are common.     

The earliest vascular land plants: continuing the search for proof

New collections from Bringewoodian strata (Silurian, Ludlow Series, Saetograptus leintwardinensis incipiens Zone) in Wales have yielded the oldest known specimens of the plant Cooksonia . From evidence at younger (Eř;éolí/Downton) horizons this genus is considered to be a vascular plant; although no tracheids have been isolated from the Bringewoodian specimens, on the basis of comparative morphology they are concluded to be the oldest recorded tracheophytes. The types of evidence relevant to the identification of vascular plants are briefly reviewed, and the relationships of the Welsh Cooksonia flora to other late Silurian floras are discussed. Confident stratigraphical dating is a prerequisite for any discussion of early plant evolution, emphasising the desirability of an integrated approach incorporating both geologial and palaeobotanical investigations. The dating of two published records of diverse Silurian floras, including lycopods, is questioned; recent dating of the Australian Baragwanathia flora as early Ludlow on the basis of graptolites is not supported by the shelly faunal evidence, which indicates a correlation within the Lower Devonian.     

Large-Scale Phylogenomic Analyses Reveal the Monophyly of Bryophytes and Neoproterozoic Origin of Land Plants

The relationships among the four major embryophyte lineages (mosses, liverworts, hornworts, vascular plants) and the timing of the origin of land plants are enigmatic problems in plant evolution. Here, we resolve the monophyly of bryophytes by improving taxon sampling of hornworts and eliminating the effect of synonymous substitutions. We then estimate the divergence time of crown embryophytes based on three fossil calibration strategies, and reveal that maximum calibration constraints have a major effect on estimating the time of origin of land plants. Moreover, comparison of priors and posteriors provides a guide for evaluating the optimal calibration strategy. By considering the reliability of fossil calibrations and the influences of molecular data, we estimate that land plants originated in the Precambrian (980–682 Ma), much older than widely recognized. Our study highlights the important contribution of molecular data when faced with contentious fossil evidence, and that fossil calibrations used in estimating the timescale of plant evolution require critical scrutiny.     

Pyrite in Silurian graptolites from Bornholm, Denmark

Pyrite is present in many horizons in dark grey graptolite-rich shales of Llandovery-early Wenlock age on the island of Bornholm, Denmark. The pyrite usually occurs as internal moulds of the graptolites, but rarely on the outside of the periderm. Occasionally the internal pyrite protrudes from the apertures of the rhabdosomes. Investigations using reflected light and scanning electron microscopy have shown that the internal pyrite is texturally variable. The abundance of the framboids is variable, ranging from thin linings on the inner side of the periderm to nearly complete infills of the graptolite colony. The pyrite also occurs as densely packed microcrystals and as larger euhedral crystals in all transitions from individual crystals, often developed on the surfaces of the framboids. to compact aggregations. Some of the pyritized graptolites have central cavities in the rhabdosomal linings. Within the cavities there are striking stalactite-like forms of pyrite suspended from the roof of the periderm. Some specimens have late infillings by calcite in the central part of the tubes. Most of the internal pyrite must have been formed very early during the taphonomic processes operating on the graptolites, pre-dating the compaction of the sediment. The framboids were first precipitated, followed by the aggregated euhedral pyrite. It is debatable whether the tubes of the graptolites were fluid-filled or partially gas-filled when the stalactites were formed; the latter is the more likely. The beds with fully pyritized graptolites might represent an episodic increase of sedimentation rate and oxygen content of bottom waters. □ Pyrite, Silurian, graptolites, Bornholm, stalactites, early diagenesis.     

A fully fertile intergeneric hybrid derivative from Argyroxiphium sandwicense SSP. macrocephalum DUBAUTIA MENZIESII(Asteraceae) and its relevance to plant evolution in the Hawaiian Islands

Achenes collected from natural putative F₁ intergeneric hybrids involving Argyroxiphium sandwicense DC. ssp. macrocephalum (A. Gray) Meyrat and Dubautia menziesii (A. Gray) Keck were germinated and grown in cultivation. One of these apparent B₁ hybrids that approached D. menziesii in morphology exhibited greatly increased fertility over the F₁ (79% vs. 9% pollen stainability), and was used as a female parent to generate a B₂ progeny by backcrossing a second time to D. menziesii. The B₂ was surprisingly uniform. One individual that flowered was fully fertile (99% pollen stainability). Its floral and vegetative features were extremely similar to those of the recurrent parent, D. menziesii. Observations suggest that plants of similar origin may exist under natural conditions and that the close relatives, D. platyphylla (A. Gray) Keck and D. dolosa (Degener & Sherff) G. Carr, may have originated from the same or a similar intergeneric hybrid combination. Because many other analogous situations occur in the silversword alliance and elsewhere in the Hawaiian flora, it is concluded that hybridization is an evolutionarily important phenomenon, especially in unstable geological systems. Although the Hawaiian archipelago is a premier example of such instability, continents are not immune to natural perturbations. Therefore, hybridization, as a mechanism that greatly extends the size of gene pools available for recombination, should also be expected to play an important evolutionary role in continental floras.     

Ordovician chitinozoans and acritarchs from southern and southeastern Turkey

Revision of the lithostratigraphy of Ordovician deposits in southern and southeastern Turkey led to a re-evaluation of the age assignments of formations identified in the subsurface and at outcrop. Previous datings were based on macrofauna (mainly trilobites and graptolites). The present paper focuses exclusively on organic-walled microfossils (chitinozoans and acritarchs), which provide numerous chronostratigraphical improvements, especially in successions barren or poor in macrofossils. Close to 200 samples were collected in the Taurus chain (i.e. from Kemer, Seydisehir, Ovacik, Kozan, to Sariz regions in southern Turkey) and in the Border Folds (Mardin and Hakkari regions), usually regarded as part of the Arabian Plate in palaeogeographical reconstructions. Many samples are productive and yield chitinozoans and/or acritarchs of extremely variable preservation, depending on their geographical and geological location. In the Taurus chain, the material is “coalified” and frequently fragmented whereas, in the Border Folds, maturation of the organic matter is much lower and preservation of the microfossils is good to excellent. Several Ordovician chitinozoan biozones (northern Gondwana zonation) as well as diagnostic acritarch assemblages are identified in southern and southeastern Turkey. These Ordovician formations are assigned here to the new global stages of the Ordovician chronostratigraphical scale. The Seydisehir (upper part), Sobova, and Kilgen Lake (lower part) formations are referred to the Darriwilian. The Kilgen Lake (upper part), Sort Tepe, and Bedinan formations are attributed to the Sandbian and to the Katian, and the Halevikdere Formation (glacio-marine part) is assigned to the Hirnantian. Reworking of Early Ordovician acritarchs is documented in pre-glacial and in glacial Late Ordovician deposits. They indicate that active erosive processes occurred during the Middle and Late Ordovician sedimentation. The organic-walled microfossils recorded in the Ordovician of south and southeastern Turkey belong to the northern Gondwana realm. Interestingly however, some Baltoscandian influences are noted in the Border Folds during Early Late Ordovician.     

Rhabdotubus, a Middle Cambrian rhabdopleurid hemichordate

Rhabdotubus johanssoni n.gen., n.sp., is described from the early Middle Cambrian Eccaparadoxides pinus Zone of Närke, southern Sweden. The colonies encrusted shells of inarticulate brachiopods, and occasionally trilobites, on otherwise soft substrates. The tubarium consists of repent and erect tubes. The former branch irregularly and produce a thecorhiza-like structure; the latter are erect and mostly isolated, up to 10 mm in length and widening gradually to about 1 mm width. Both repent and erect tubes are composed of fusellar bands, mostly irregularly arranged. Branching of repent tubes takes place through resorption or perforation of fusellar tissue in the parent tube. Branching of erect tubes occurs sporadically. There is no thecal dimorphism. No sclerotized stolon is present. Rhabdotubus is interpreted as the earnest known rhabdopleurid (Class Pterobranchia, Phylum Hemichordata). In general habitus it is similar to sessile graptolites of the Order Tuboidea. These similarities may well have phylogenetic significance, but further knowledge of the Tuboidea and other sessile orders of the Graptolithina is required to clarify the early evolution of graptolites.     

A late Wenlock flora from Co. Tipperary, Ireland

An assemblage of macroplants preserved as highly coalified compressions which lack anatomy is described from a Wenlock locality in County Tipperary, Ireland. Most of the fertile specimens are assigned to Cooksonia Lang. The taxonomic status of this genus is discussed. Some poorly preserved palynomorphs, including miospores, acritarchs, chitinozoans and a variety of tubes, have been isolated from associated sediments, but the age of the flora is based on graptolites. Sedimentological and palaeontological studies of the region are summarized. They provide little direct evidence for the habitats of the plants which are considered to have been terrestrial. The relevance of this flora to the current debate on the colonization of the land is evaluated and it is concluded that these plants provide the earliest record of erect fertile land plants of possible pteridophyte affinity.     

Regeneration Around Wounds and the Control of Vascular Differentiation

The question which was the basis of this work was whether (a)vascular regeneration around wounds includes a replacement ofdamaged tissues or (b) only new vascular strands, which arenormally formed from the cambium, are diverted around wounds.It was found that in Coleus and Cucumis no connections are formedto damaged sieve tubes and vessels, so that their continuityaround wounds is not restored. Pisum plants were wounded underconditions in which growth could not be influenced and the areaof the xylem in cross-section was measured 1 month later. Thewounds, which damaged the vascular tissues, significantly increasedvascular differentiation, indicating the replacement of a longnon-functional region of damaged tissues. The results indicatethat in the intact plant vascular differentiation is controllednot only by stimuli from the leaves but also by the capacityof the mature vascular system to transport these stimuli.     

Production of in vitro haploid plants from in situ induced haploid embryos in winter squash (<Emphasis Type="Italic">Cucurbita maxima</Emphasis> Duchesne ex Lam.) via irradiated pollen

The influence of pollen irradiation on the production of in vitro haploid plants from in situ induced haploid embryos was investigated in winter squash (Cucurbita maxima Duchesne ex Lam.). Pollen were irradiated at different gamma-ray doses (50, 100, 200 and 300 Gray) and durations (9, 11, 15, 21, and 28 July). Production of in vitro haploid plantlets was influenced by irradiation dose, irradiation duration, genotype, and embryo type and embryo stage. Embryos were only obtained from lower irradiation doses (50 Gray and 100 Gray) and earlier irradiation durations (9, 11, and 15 July). The greatest embryo number per fruit was procured from “G14” and “55SI06” genotypes at 50 Gray gamma-ray dose. Necrotic embryos were higher than normal embryos at delayed harvest times (5 and 6 weeks after the pollination). The convenient harvest time for embryo rescue was observed about 4 weeks (between 25 and 30 days) after pollination. All cotyledon and amorphous embryos had only diploid plants while late-torpedo, arrow-tip, and pro-cotyledon embryos produced 33.3, 50.0, and 66.7% haploid plant. The frequency of haploid plantlets was 0.11, 1.17, 10.96 and 0.28 per 100 seeds, 100 embryos, 100 plantlets and a fruit at 50 Gray gamma-ray dose, respectively.     

Effects of neighboring plants on the growth and reproduction of <Emphasis Type="Italic">Deschampsia antarctica</Emphasis> in Antarctic tundra

Populations of the two native vascular plant species on the Antarctic Peninsula have increased over the past 40 years. This increase has been attributed to improved reproductive performance resulting from regional warming and increased growing season length. However, little is known of the influence that vascular plants have on the performance of neighboring plants in developing and well-established communities. We compared the aboveground growth and reproduction of Deschampsia antarctica plants growing alone or in close proximity to neighboring plants (D. antarctica, Colobanthus quitensis, or mosses) at a young, recently colonized and an older, well-developed plant community on the Antarctic Peninsula to assess whether neighboring plants had a positive or negative effect on D. antarctica performance, and whether these effects varied from young to old communities. In both communities, tillers on D. antarctica plants near neighbors produced 48–89% fewer leaves and 49–93% fewer tillers than those on D. antarctica plants growing alone. These tillers also had relative growth rates that were 25–66% lower- and tiller-size indices that were 42–87% less than those on plants growing alone. In addition, the biomass of tillers on plants growing near neighbors was 40–91% lower than those on plants growing alone. Leaf and tiller production was generally higher in the older, more developed community than in the younger community. Our findings illustrate that vegetative growth of D. antarctica is reduced when growing in close proximity to neighboring plants, suggesting that negative plant interactions are an important constraint at our field sites.     

Transfer of water from roots into dry soil and the effect on wheat water relations and growth

This investigation was performed to study the effect on plant water relations and growth when some of roots grow into dry soil. Common spring water (Triticum aestivum) plants were grown from seed in soil in 1.2 m long PVC (polyvinyl chloride) tubes. Some of the tubes had a PVC partition along their center so that plants developed a split root system (SPR). Part of the roots grew in fully irrigated soil on one side of the partition while the rest of the roots grew into a very dry (-4.1 MPa) soil on the other side of the partition. Split root plants were compared with plants grown from emergence on stored soil moisture (STOR) and with plants that were fully irrigated as needed (IRR). The experiment was duplicated over two temperature regimes (10°/20°C and 15°/25°C, night/day temperatures) in growth chambers. Data were collected on root dry matter distribution, soil moisture status, midday leaf water potential (LWP), leaf relative water content (RWC) and parameters of plant growth and yield.Some roots were found in the dry side of SPR already at 21 DAE (days after emergence) at a soil depth of 15 to 25 cm. Soil water potential around these roots was -0.7 to -1.0 MPa at midday, as compared with the initial value of -4.1 MPa. Therefore, water apparently flowed from the plant into the dry soil, probably during the night. Despite having most of their roots (around 2/3 of the total) in wet soil, SPR plants developed severe plant water stress, even in comparison with STOR plants. Already at 21 DAE, SPR plants had a LWP of -1.5 to -2.0 MPa, while IRR and STOR had a LWP of -0.5 MPa or higher. As a consequence of their greater plant water stress, SPR as compared with IRR plants were lower in tiller number, ear number, shoot dry matter, root dry matter, total biomass, plant height and grain yield and had more epicuticular wax on their leaves.It was concluded that the exposure of a relatively small part of a plant root system to a dry soil may result in a plant-to-soil water potential gradient which may cause severe plant water stress, leading to reduced plant growth and yield.     

Major Evolutionary Trends in Hydrogen Isotope Fractionation of Vascular Plant Leaf Waxes

Hydrogen isotopic ratios of terrestrial plant leaf waxes (δD) have been widely used for paleoclimate reconstructions. However, underlying controls for the observed large variations in leaf wax δD values in different terrestrial vascular plants are still poorly understood, hampering quantitative paleoclimate interpretation. Here we report plant leaf wax and source water δD values from 102 plant species grown in a common environment (New York Botanic Garden), chosen to represent all the major lineages of terrestrial vascular plants and multiple origins of common plant growth forms. We found that leaf wax hydrogen isotope fractionation relative to plant source water is best explained by membership in particular lineages, rather than by growth forms as previously suggested. Monocots, and in particular one clade of grasses, display consistently greater hydrogen isotopic fractionation than all other vascular plants, whereas lycopods, representing the earlier-diverging vascular plant lineage, display the smallest fractionation. Data from greenhouse experiments and field samples suggest that the changing leaf wax hydrogen isotopic fractionation in different terrestrial vascular plants may be related to different strategies in allocating photosynthetic substrates for metabolic and biosynthetic functions, and potential leaf water isotopic differences.