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Roberto R. Pujana and Daniela P. Ruiz

ABSTRACT

Over 80 samples of fossil woods were collected from numerous outcrops of the Río Turbio Formation, southwestern Patagonia. Preservation of the woods is variable and only about half of these samples could be identified to genus level. The assemblage consists of six types of conifers and four types of dicotyledons, one of them a new species of Caldcluvioxylon (Cunoniaceae). We provide an emended diagnosis of Caldcluvioxylon. A previously described fossil wood from this stratigraphic unit, thought to have affinity with Proteaceae, was re-examined and is described herein as Scalarixylon romeroi sp.nov. Other families recognized in the Río Turbio Formation wood assemblage are Araucariaceae, Podocarpaceae, and Nothofagaceae. Differences in the taxonomic composition of the upper and lower members of the Río Turbio Formation are consistent with the age difference between them according to recent isotopic dating. The diversity of fossil wood is also consistent with the fossil leaves and pollen from each stratigraphic level and most of the taxa are shared with coeval Antarctic fossil wood floras.

Anne-Laure Decombeix, Anaïs Boura and Alexandru M. F. Tomescu

ABSTRACT

Studies of anatomically preserved fossils provide a wealth of information on the evolution of plant vascular systems through time, from the oldest evidence of vascular plants more than 400 million years ago to the rise of the modern angiosperm-dominated flora. In reviewing the key contributions of the fossil record, we discuss knowledge gaps and major outstanding questions about the processes attending the evolution of vascular systems. The appearance and diversification of early vascular plants in the late Silurian-Devonian was accompanied by the evolution of different types of tracheids, which initially improved the hydraulics of conduction but had less of an effect on mechanical support. This was followed in the Devonian and Carboniferous by an increase in complexity of the organization of primary vascular tissues, with different types of steles evolving in response to mechanical, hydraulic, and developmental regulatory constraints. Concurrently, secondary vascular tissues, such as wood, produced by unifacial or bifacial cambia are documented in a wide array of plant groups, including some that do not undergo secondary growth today. While wood production has traditionally been thought to have evolved independently in different lineages, accumulating evidence suggests that this taxonomic breadth reflects mosaic deployment of basic developmental mechanisms, some of which are derived by common ancestry. For most of vascular plant history, wood contained a single type of conducting element: tracheids (homoxyly). However, quantitative (e.g. diameter and length) and qualitative (e.g. pitting type) diversity of these tracheids allowed various taxa to cover a broad range of hydraulic properties. A second type of conducting elements, vessels, is first documented in an extinct late Permian (c. 260 Ma) group. While the putative hydraulic advantages of vessels are still debated, wood characterized by presence of vessels (heteroxyly) would become the dominant type, following the diversification of angiosperms during the Cretaceous.

Mathew R. Vanner

Edited by Elisabeth A. Wheeler

ABSTRACT

Angiosperm wood from the Miocene Landslip Hill silcrete, Southland, New Zealand is described. It is characterised by solitary vessels of two distinct size classes; rays of two size classes alongside aggregate rays; simple perforation plates; and axial parenchyma in tangential bands up to three cells wide. The wood has features similar to Casuarinaceae and is described here as a new species, Casuarinoxylon ildephonsi. The fossils were collected as isolated fragments of wood; there is no directly associated cladode or cone material although isolated fragments of these are common elsewhere in the Landslip Hill silcrete. This is the second record of fossil Casuarinaceae wood from New Zealand and the first sample to be anatomically described. Currently, Casuarinaceae does not occur in New Zealand. Casuarinoxylon ildephonsi would have grown in a warm temperate to subtropical climate on an open deltaic floodplain.

Mélanie Tanrattana, Jean-François Barczi, Anne-Laure Decombeix, Brigitte Meyer-Berthaud and Jonathan Wilson

Edited by Lisa Boucher

ABSTRACT

The origin of xylem in the Silurian was a major step in plant evolution, leading to diverse growth forms with various mechanical and hydraulic properties. In the fossil record, these properties can only be investigated using models based on extant plant physiology. Regarding hydraulics, previous studies have considered either the properties of a single tracheid or of a set of independent tubes. Here, we use the analogy between the flow of water under tension in a plant and an electrical circuit to develop an extension of Wilson’s single tracheid model to the tissue scale. Upscaling to the tissue-level allows considering wood as a heterogeneous tissue by taking into account differences in tracheid density and the presence of rays. The new model provides a more biologically accurate representation of fossil wood hydraulic properties. The single tracheid and new tissue models are applied to two conspecific specimens of Callixylon (Progymnospermopsida, Archeopteridales) from the Late Devonian of Morocco. Differences are shown at the tissue level that cannot be suspected at the single tracheid level. Callixylon represents the first trees with a conifer-like wood and is a major component of Late Devonian floras world-wide. Our results show that the anatomical disparity of its wood might have led to hydraulic plasticity, allowing growth in various environmental conditions. More generally, the new tissue-model suggests that the various combinations of tracheid and ray sizes present in Palaeozoic plants might have led to a higher variety of ecophysiologies than suspected based solely on the properties of individual tracheids.

A. Boura, G. Saulnier, D. De Franceschi, B. Gomez, V. Daviero-Gomez, D. Pons, G. Garcia, N. Robin, J-M. Boiteau and X. Valentin

ABSTRACT

Thousands of silicified wood fragments were recently collected from the middle Cenomanian of Vienne in western France at less than 10 km away from a historical locality where in 1870 the French geologist Alphonse Le Touzé de Longuemar reported silicified wood. The plant assemblage is very diverse, and includes several species of ferns, conifers, and angiosperms. We describe and discuss the systematic affinities of a new vesselless angiosperm. Many of its characters are shared by extant and fossil Winteraceae. Nevertheless, the absence of uniseriate rays makes the anatomy of these specimens unique. Its combination of characters justifies the establishment of a new genus of vesselless fossil angiosperm wood of uncertain affinity, Sherwinoxylon gen. nov.

Yiftach Vaknin and Irina Mogilevski

Adaptive variation of plant species is best evaluated under environmental gradients. Silybum marianum is a native to the Mediterranean basin, distributed continuously along an aridity gradient from northern Israel to the edge of the Negev desert. To elucidate the adaptive significance of traits associated with proximity to the desert and with increasing levels of aridity, we compared northern populations from the mesic Mediterranean end of the aridity gradient with southern, adjacent to the Negev desert populations, from the arid end. The F1 self-progeny of all populations were evaluated under open field conditions. Plants originated from southern populations grew taller and narrower, completed their life cycle earlier, and produced more abundant, smaller achenes, with a higher content of polyphenols, which grew into smaller seedlings. Correlative analysis revealed a latitudinal cline towards the desert, of a longer life cycle, and fewer, heavier, better germinating achenes, which grew into larger seedlings. We concluded that the proximity to the desert was reflected in the appearance of genotypes with improved chances of survival under arid conditions and with higher contents of polyphenols.

Noga Sikron-Persi, Gila Granot, Gideon Grafi and Aaron Fait

The biochemical composition of Zygophyllum dumosum Boiss (Zygophyllaceae) was analyzed in petioles collected in the summer and winter from plants growing in a natural ecosystem on a southeast-facing slope of the Negev desert. UPLC-QTOF MS based analysis identified season specific sulfur containing phenylpropanoids unreported in plants. Sulfuric-caffeic and -ferulic acid derivatives and isorhamnetin 3-O-(4-sulfate-rutinoside) were measured to accumulate specifically in the summer. The reported identification and accumulation of sulfate containing metabolites during the hot and dry summer can be related to the putative protective role reported for these compounds.

Oz Barazani and Jotham Ziffer-Berger

Sofia Shevtsov, Omer Murik, Hagit Zer, Ofir Weinstein, Nir Keren, Ori Fragman-Sapir and Oren Ostersetzer-Biran

The sparsely distributed Limodorum abortivum is a European-Mediterranean orchid species, which grows on decomposing plant material. Although some chlorophyll-pigmentation is observed in the degenerated scales-shaped leaf and stems regions of the plant, its photosynthetic capacity is assumed to be insufficient to support the full energy requirements of an adult plant. In Israel, L. abortivum shows a patchy distribution patterns in the Galilee, Golan, Carmel and Judean regions. To gain more insights into the physiology and photosynthetic activity of L. abortivum, we analyzed the organellar morphologies, photosynthetic activities the chloroplast-DNA sequence by Illumina-HTS. Microscopic analyses indicated to the presence of mature chloroplasts with well-organized grana-thylakoids in the leaves and stems of L. abortivum. However, the numbers of chloroplasts per cell and the grana ultrastructure density within the organelles were notably lower than those of model plant species and fully photosynthetically-active orchids. The cpDNA of L. abortivum (154,954 bp) encodes 60 proteins, 34 tRNAs and 4 rRNAs. The coding-regions of 24 genes are interrupted by 26 group-II intron-sequences. While many genes related to photosynthesis (RuBisCo, PSI, PSII and cytochrome b 6 /f subunits) have remained intact in the cpDNA, the majority of the NADH-dehydrogenase (ndh) subunits were either lost or became nonfunctional (i.e. pseudogenized). In agreement with previous reports, the photosynthetic-rates of adult Limodorum plants were found to be very low, further indicating that carbon-assimilation activity is insufficient to support the energy requirements of an adult plant, and may suggest that L. abortivum have adopted nutritional strategies similar to that of mycoheterotrophic orchid species.

Simcha Lev-Yadun

Several types of defensive Batesian mimicry seem to be much more common in plants than was historically and is currently considered. It is based either on visual aspects (shape, coloration, and even movement), on odors, and on combinations of both these sensing modalities. Various characters that seem to function as defensive Batesian mimicry, may also simultaneously take part in pollination, physiological functions, or in other defensive mechanisms. The defended models for the visual Batesian mimics in plants belong to several categories: (1) spiny, thorny and prickly plant species, (2) mechanically or chemically defended parts of the same individual plant, or other members of the same species (auto mimicry), (3) colorful and chemically defended plants, (4) dangerous animals (aggressive, toxic), (5) fungal attacks, (6) animal action and animal damage cues, and (7) oozing defensive white latex. Olfactory defended models include: (1) toxic plants, (2) animal alarm pheromones, and (3) animal carrion and feces odors. Many more descriptive, genetic, phylogenetic and experimental studies have to be done in order to better understand the role of defensive Batesian mimicry in plant biology.