Axial Parenchyma Research Articles

A new genus of Anacardiaceae fossil wood from El Bosque Formation (Eocene), Chiapas, Mexico

ABSTRACTWe describe a new fossil wood from the El Bosque Formation (Eocene) in Chiapas, southern Mexico. It has a combination of features found in the Anacardiaceae, including distinct growth rings, diffuse porosity, vessels solitary and in radial multiples of 2–3, simple perforation plates, medium to large alternate intervessel pits, vessel-ray parenchyma pits rounded and elongate with reduced borders, septate and non-septate fibers, axial parenchyma scanty paratracheal, vasicentric, apotracheal diffuse, Kribs heterogeneous rays type IIA, and multiseriate rays with radial canals. The mosaic of features of this wood supports the erection of a new genus, Bosquesoxylon Pérez-Lara, Castañeda-Posadas et Estrada-Ruiz. This new genus of anacardiaceous fossil wood extends our knowledge of this family’s history and offers hints on the possible relationships with floras from other localities worldwide, especially North America and Asia.

Development of successive cambia and formation of flat stems in Rhynchosia pyramidalis (Lam.) Urb. (Fabaceae)

Stem flattening in Rhynchosia pyramidalis (Fabaceae) is achieved by the development of crescent-shaped successive cambia on two opposite sides of the stem (referred hereafter as distal side). Other lateral sides of the stem (adjacent to supporting host and its opposite side, referred as proximal sides) usually possess single cambium. In the young stems, parenchymatous cells located outside to protophloem of distal side dedifferentiate and develop small segments of cambium. Concomitant to bidirectional differentiation of the secondary xylem and phloem, these newly developed cambial segments also extend in tangential directions. Differential activity of newly developed crescent-shaped cambial segments deposits more secondary xylem at median position as compared to their terminal ends of the stem on distal side; consequently, it pushes the cambial segment outside, thus resulting in crescent-shaped arcs of the cambia only on two opposite sides. After the production of 1–2 mm of secondary xylem, they cease to divide and new segments of cambial arc develop on the same side in a similar fashion. Such repeated behaviour of successive cambia development consequently leads to the formation of tangentially flat stems. The secondary xylem is diffusely porous with indistinct growth rings and is composed of vessels (wide and narrow), fibres, axial ray parenchyma cells, while phloem consisted of sieve elements, companion cells, axial and ray parenchyma. Rays in both xylem and phloem are uni- to multiseriate and heterocellular. The structure of secondary xylem and development of successive cambia is correlated with climbing habit.

Redescription and reassignment of the fossil wood Menendoxylon piptadiensis from the Pliocene Andalhuala Formation, South America

A restudy of the holotype of the fossil wood Menendoxylon piptadiensis Lutz, 1987 has revealed that this taxon possesses several diagnostic anatomical features not associated with Leguminoseae-Mimosoideae to which it was originally referred. The combined presence of laticiferous tubes, axial parenchyma apotracheal diffuse and paratracheal vasicentric, strands of 2–7 cells, homocellular rays, simple perforation plates, vestured intervessel pits, and non-septate fibres with distinctly bordered pits are diagnostic characteristics that support its transfer to the family Apocynaceae and a particular resemblance with species of the tribe Willughbeieae within the subfamily Rauvolfioideae. The fossil is closest to Parahancornia fasciculata, Parahancornia peruviana and Couma guianensis, with anatomical characteristics especially similar those of Parahancornia fasciculata. The extant Parahancornia is most closely related to the fossil, supporting the hypothesis that this genus was more widespread in the past. Currently, it is distributed in the Neotropics, temperate Brazil and tropical South America (northern Bolivia, north-eastern Perú, Colombia and Guayana). The material studied here is the first fossil wood from South America with an affinity to Apocynaceae and a new combination is erected, Parahancornioxylon piptadiensis (Lutz) Moya & Brea gen. et comb. nov. Eco-anatomical characteristics, Carlquist's index and the nearest living relatives (NLRs) indicate a warmer and more humid climate in north-west Argentina during the Pliocene, probably associated with tropical forests.

Vessel diameter is related to amount and spatial arrangement of axial parenchyma in woody angiosperms.

Parenchyma represents a critically important living tissue in the sapwood of the secondary xylem of woody angiosperms. Considering various interactions between parenchyma and water transporting vessels, we hypothesize a structure-function relationship between both cell types. Through a generalized additive mixed model approach based on 2,332 woody angiosperm species derived from the literature, we explored the relationship between the proportion and spatial distribution of ray and axial parenchyma and vessel size, while controlling for maximum plant height and a range of climatic factors. When factoring in maximum plant height, we found that with increasing mean annual temperatures, mean vessel diameter showed a positive correlation with axial parenchyma proportion and arrangement, but not for ray parenchyma. Species with a high axial parenchyma tissue fraction tend to have wide vessels, with most of the parenchyma packed around vessels, whereas species with small diameter vessels show a reduced amount of axial parenchyma that is not directly connected to vessels. This finding provides evidence for independent functions of axial parenchyma and ray parenchyma in large vesselled species and further supports a strong role for axial parenchyma in long-distance xylem water transport.

New insights on the stepwise collapse of the Carboniferous Coal Forests: Evidence from cyclothems and coniferopsid tree-stumps near the Desmoinesian–Missourian boundary in Peoria County, Illinois, USA

The first phase in the stepwise collapse of the Carboniferous Coal Forests occurred near the Desmoinesian–Missourian boundary (early Kasimovian, ~307Ma), and involved extirpation of Lycospora-producing lepidodendrids, and some other lycopsids, across most of tropical Euramerica. In this paper, we follow-up on historical reports of silicified tree-stumps in Peoria County, northwest-central Illinois, USA, which have significant implications for understanding Carboniferous Coal Forest collapse. Rooted near the paleoweathered top of the Lonsdale Limestone, and widespread across an area of ~250km2, the silicified tree-stumps belong to Amyelon-type coniferopsids. A key feature of the fossil wood is the occurrence of abundant axial parenchyma arranged along irregular growth interruptions, suggestive of climatic seasonality, an inference consistent with silicic preservation. The silicified fossil forest directly underlies the Exline Limestone and Athensville Coal, the horizons that mark the US-wide loss of Lycospora, and demonstrate that lowland areas were colonized by dryland coniferopsid forests following Coal Forest collapse. Placed in a cyclothem context, the silicified fossil forest horizon lies above the Maria Creek mudstone paleosol (top of Piasa cyclothem), in which earlier d18O analyses have identified a major pulse of global warming, and coincides with the ‘Hanna City’ paleosol (top of Lonsdale cyclothem), which is correlative with the Seminole Sandstone, a Midcontinent incised valley-fill representative of one of the most profound glacioeustatic falls seen in the Pennsylvanian record. Our new findings therefore demonstrate that Coal Forest collapse was closely linked to intensification of glacial cycle amplitude near the Desmoinesian–Missourian boundary, involving both extreme episodes of global warming and cooling.

Radial variation of wood functional traits reflect size‐related adaptations of tree mechanics and hydraulics

Abstract Wood serves for mechanical support, water transport and storage. These functions are provided for by different cells with a large variation in wood anatomy among species but also within individual trees. The latter often reflects ontogenetic adjustments, related to tree size or age, which can be studied by looking at patterns of radial variation in wood. We quantified radial variation in wood density (WD) and wood anatomy and ask how ontogenetic changes of wood functions are controlled in five canopy tree species in western Thailand. We ask if there are trade‐offs between these main functions of wood, how ontogenetic trends are linked to differences in growth trajectories and shade tolerance among tree species and if wood properties are mainly controlled by tree age or by size. In all species studied, vessel fraction, vessel size, theoretical hydraulic conductivity (Kh) and fibre wall thickness significantly increased with tree diameter. While the ray fraction also increased in all species except Neolitsea, axial parenchyma changed significantly only in Afzelia, the species with by far the largest axial parenchyma fraction. The average WD and Kh reflect the phenology, with deciduous and shade‐intolerant Toona and Melia having low WD and high Kh, and shade‐tolerant brevi‐deciduous Chukrasia and evergreen Neolitsea having higher WD and low Kh. Deciduous Afzelia, however, had the lowest Kh and second‐highest WD. The radial gradients in WD and Kh also reflect within‐species differences in growth rates during ontogeny. The relationship between WD and its underlying anatomical components varied substantially among species. Modulating fibre wall thickness and vessel size enables growing trees to increase water transport capacity and mechanical strength at the same time. Across species, tree diameter had a stronger effect than age on all parameters except for fibres. Given the very substantial within‐tree size‐related variation in wood traits, tree size is an essential parameter to include in comparative studies on the functional ecology of wood. Analysing ontogenetic changes in wood can advance our understanding of the different ecological strategies of trees. A plain language summary is available for this article.

Caracterização anatômica macroscópica do lenho de árvores de espécies de canela, Ocotea e Nectandra (Lauraceae) ocorrentes no estado de Santa Catarina

As árvores conhecidas popularmente por “canela”, pertencentes aos gêneros Ocotea e Nectandra (Lauraceae), são de difícil separação tanto em nível de gênero como de espécie, pela anatomia do seu lenho. O presente trabalho tem como objetivo descrever os caracteres anatômicos macroscópicos e organolépticos do lenho e sua aplicação na identificação dos gêneros e das espécies desta família. Foram coletados discos do lenho à altura do peito (1,30 m) do tronco das árvores de Nectandra megapotamica, N. lanceolata, Ocotea porosa, O. puberula, O. pulchella e Ocotea sp. ocorrentes em quatro municípios do interior do estado de Santa Catarina. As características anatômicas macroscópicas e organolépticas do lenho foram descritas de acordo com as normas usuais para estudos em anatomia da madeira, cujos resultados indicam a possibilidade de separação de Nectandra e de Ocotea tais como visibilidade do parênquima axial, arranjo diagonal dos vasos, cor e cheiro do lenho. Apresenta-se, ainda, uma chave dicotômica que permite a separação das árvores das espécies de Lauráceas estudadas. No trabalho, conclui-se que as seis espécies analisadas podem ser identificadas pela estrutura anatômica observada macroscopicamente e propriedades organolépticas do seu lenho, não sendo encontrados, no entanto, caracteres que propiciem a distinção dos gêneros Ocotea e Nectandra entre si.

Fossil woods of Detarioideae subfamily (Fabaceae) from El Palmar Formation (Late Pleistocene) in South America

The main aim of the present paper is to describe the first Detarioideae fossil woods from El Palmar Formation (Late Pleistocene) in the Uruguay River Basin (Entre Ríos, Argentina). This study is based on five silicified wood specimens preserved in fluvial deposits, which were transported from their growth site. Two new genera and species are described: Paraoxystigma concordiensis gen. nov and sp. nov. has medium-sized vessels, paratracheal axial parenchyma, heterocellular and multiseriate rays, and diffuse axial canals similar in size and shape to vessels, and Gossweilerodendroxylon palmariensis gen. nov and sp. nov. has medium-sized vessels, alternate intervessel pits, paratracheal and apotracheal axial parenchyma, homocellular and uni to-multiseriate rays, and small diffuse axial canals. These Detarioideae fossil records in south-eastern South America support the existence of a very old relationship with the extant West African forests. Eco-anatomical features observed in these fossil woods, along with the climatic information available from the Nearest Living Relatives (NLRs) comparison, suggest warm and humid climatic conditions for the upper-middle basin of the Uruguay River during some periods of the Late Pleistocene.

Transcriptomic analysis of juvenile wood formation during the growing season in Pinus canariensis

Abstract A noticeable proportion of low transcribed genes involved in wood formation in conifers may have been missed in previous transcriptomic studies. This could be the case for genes related to less abundant cell types, such as axial parenchyma and resin ducts, and genes related to juvenile wood. In this study, two normalized libraries have been obtained from the cambial zone of young individuals of Pinus canariensis C. Sm. ex DC, a species in which such cells are comparatively abundant. These two libraries cover earlywood (EW) and latewood (LW) differentiation, and reads have been de novo meta-assembled into one transcriptome. A high number of previously undescribed genes have been found. The transcriptional profiles during the growing season have been analyzed and several noticeable differences with respect to previous studies have been found. This work contributes to a more complete picture of wood formation in conifers. The genes and their transcription profiles described here provide a useful molecular tool for further studies focused on relevant developmental issues, such as wound response and the formation of traumatic wood, re-sprouting, etc., presumably related to those cells.

Malvaceous wood from the Late Pleistocene El Palmar Formation of northeastern Argentina

We describe a new species of Bastardiopsis, Bastardiopsis palaeodensiflora sp. nov., which is the first fossil Malvaceae wood reported in Argentina. It was collected from the Arroyo Yuquerí of El Palmar Formation, a late Quaternary fluvial unit, located in the middle Uruguay River Basin, NE Argentina. The diagnostic features of this fossil wood are growth ring boundaries demarcated by marginal parenchyma; diffuse porous wood; vessels solitary and in radial multiples of 2–3 elements; alternate and minute-to-small sized intervessel pits; tyloses abundant; vessel-ray parenchyma pits similar in size and shape to intervessel pits; vasicentric, and diffuse axial parenchyma; rays of two distinct sizes, mostly 4–5 cells wide; prismatic crystals in upright and/or square marginal cells, sheath cells, non-septate fibres, rays and vessel elements irregularly storied. These features suggest an assignation to Bastardiopsis (K. Schumann) Hassler, a genus with five extant species, extending from the north of South America to northern Argentina, mainly distributed in tropical to temperate areas. The eco-anatomical features, the Nearest Living Relatives (NLRs), the Vulnerability Index, the Mesomorphy ratios and the Taxon Independent Approach (TIA) indicate that this fossil grew under temperate-warm and humid conditions. This is consistent with other proxies (geological, sedimentological and microfossil data) suggesting a similar environment for this region during some periods of the Late Pleistocene.

Characterization of density and selected anatomical features of stemwood and branchwood of E. cylindricum, E. angolense and K. ivorensis from natural forests in Ghana

This study investigated density and some anatomical features, and also assessed the correlations among them in stem and branch woods of Entandrophragma cylindricum, Entandrophragma angolense and Khaya ivorensis. Branch and stem wood samples were sampled from two natural forest reserves. Wood density was determined in accordance with ISO 3131 whereas anatomical investigations followed IAWA committee’s recommendations-1989. Results indicated that at 5% level of significance, wood density was significantly higher in branchwood than stemwood for all three species. Generally for all the three species, significant differences were found in fibre length and vessel diameter between branchwood and stemwood of same species but no significant differences were found in both ray and axial parenchyma quantities. Stemwood density correlated significantly and positively with fibre (r = 0.408, p < 0.01) and ray parenchyma (r = 0.280, p < 0.05) proportions but negatively with fibre length (r = −0.528, p < 0.01), vessel lumen diameter (r = −0.304, p < 0.05) and axial parenchyma proportion (r = −0.679, p < 0.01). However, branchwood density correlated significantly and positively with fibre (r = 0.505; p < 0.01) and axial parenchyma (r = 0.385; p < 0.01) proportions but negatively with fibre length (r = −0.316, p < 0.05), vessel proportion (r = −0.486, p < 0.01) and ray parenchyma proportion (r = −0.357, p < 0.01). The study suggests that wood type (stem or branch) is an important factor to consider in terms of their effect on some properties of products produced from them, since differences in fibre length, vessel lumen diameter and vessel proportion could affect strength, porosity, leachability, natural durability and drying properties of wood.

Duration of cambial activity is determined by water availability while cambial stimulus is day-length dependent in a Neotropical evergreen species

Experimental manipulations are essential for understanding the causal factors of plant growth and cambial activity. Here, we studied the potential effect of water availability and natural variation of day length and temperature on cambial activity in Cordiera concolor (Cham.) Kuntze, an evergreen tropical species. Experiments were conducted in a greenhouse using ninety one-year-old plants divided into two groups. Each group was observed for five weeks during two different times of the year (early spring and late summer). Plants were subjected to three distinct water regimes (waterlogging, field capacity and water deficit). Temperature and day length were recorded daily and stem samples were taken weekly during both sampling intervals. Anatomical procedures were used to describe the cambial activity per stem. Our results suggest that soil water content and its influence on cambial activity depend on the time of year, while cambial stimulus was positively related to day length, independent of the time of year. In early spring, cambial activity was stimulated by an increase of day length, regardless of water supply. In contrast, in late summer, cambial dormancy was delayed in waterlogged plants and advanced in plants subjected to a water deficit, followed by decreasing day length. Analyses of the wood anatomy showed that the marginal bands of axial parenchyma were initial. Our study highlights a more complex scenario of plant functioning and its causal factors in tropical systems.

First Lower Cretaceous record of Podocarpaceae wood associated with dinosaur remains from Patagonia, Neuquén Province, Argentina

The first Podocarpaceae wood record is described from the Mulichinco Formation (Valanginian, Lower Cretaceous), Neuquén Basin, Argentina. The specimen was directly associated with a middle caudal vertebra of a diplodocid sauropod dinosaur. A new species – Podocarpoxylon prumnopityoides – is proposed based on features that include the presence of abietinean wood type (tracheid radial pitting), plus podocarpoid (cupressoid type) and some dacrydioid (taxodioid type) cross-field pits, diffuse axial parenchyma and low rays. This combination of anatomical characters is comparable to both Prumnopitys and Podocarpus, whereas the type of pits in the cross-fields resembles some members of the extant Prumnopitys. This is the first unequivocal record of the Family Podocarpaceae in the Valanginian of South America and confirms the hypothesis that the divergence between the “Podocarpoid-Dacrydioid” and “Prumnopityoid” clades occurred earlier than the Early Cretaceous.

Bark anatomy ofAdansonia digitataL. (Malvaceae)

The bark structure of Adansonia digitata L. is described in detail. Characters of the bark that are shared with other Malvaceae include the presence of strongly dilating rays, mucilage cells and cavities, druses of calcium oxalate in the cells of cortical parenchyma and phloem rays, a storied arrangement of sieve tube members and axial parenchyma strands, the presence of secondary phloem fibers and their arrangement into tangential bands. The secondary phloem fibers are longer (2.8–8.6 mm) and more abundant than the libriform fibers (1.7–2.2 mm) in the wood of this species. The abundance of parenchyma in both axial and radial parts of the secondary phloem and in the pseudocortex is a noteworthy feature. Due to the complementarity of fibrous and parenchymatous tissues, the secondary phloem can provide substantial mechanical benefits and apparently play an important role in the biomechanical stability of the trunk. The meristematic capacity of dilated phloem rays and the pseudocortex allow for substantial bark dilatation with very limited abscission of the outer portions of the secondary phloem. Subsequent phellogen initiation in the outer part of the secondary phloem was not observed, not even in mature bark. Hence no rhytidome is present. The thin translucent phellem, formed by continuous phellogen arising in the subepidermal layer, allows for photosynthesis to potentially occur within the chloroplast-containing cells of phelloderm and pseudocortex, even when the plants are leafless, thus probably assisting them to survive harsh climatic conditions. The formation of sieve tube members by transverse anticlinal divisions from fusiform cambial initials in A. digitata is a first report for the Malvaceae sensu lato.

Podocarpoxylon Gothan reviewed in the light of a new species from the Eocene of Patagonia

A new species of Podocarpoxylon Gothan is described based on samples collected from sediments of the Río Turbio Formation. The fossil-bearing strata are lower Eocene (47–46 Mya) according to recent geochronological ages. The new species has indistinct growth ring boundaries, abundant and frequently tangentially zonate axial parenchyma, uniseriate pitting on radial walls, one half-bordered pit (= oculipore) with reduced borders and vertical aperture inclination per cross-field and medium height uniseriate rays. The new material is compared with all fossil-species of Podocarpoxylon and an inventory of all Podocarpoxylon species previously described is provided. Cross-field characters of the new species indicate affinity to the Podocarpaceae. The presence of Podocarpaceae wood augments other evidence of this family from the same stratigraphic unit.

Trabeculae and Al-accumulation in the wood cells of Melastomataceae species from Brazilian savanna

Family Melastomataceae is an important component of the Brazilian Cerrado flora, inhabiting different environments from those with well-drained soils to swamp soil sites. Several members of this family are recognized as aluminum (Al)-accumulating. We studied the wood anatomy of six species of Melastomataceae (Miconia albicans (Sw.) Triana, M. fallax DC., M. chamissois Naudin, M. ligustroides (DC.) Naudin, Microlepis oleaefolia (DC.) Triana, Rhynchanthera dichotoma DC.), growing in different environments of Cerrado, exploring the occurrence of trabeculae and Al-accumulation sites. We processed the material following the usual techniques in wood anatomy and histochemistry. We used a chrome azurol-S spot-test in fresh material to detect Al-accumulation. The common features were diffuse porosity, vessel elements with simple perforation plates and vestured pits, abundant parenchyma-like fiber bands and septate fibers, axial parenchyma scanty to vasicentric, and heterocellular rays. The presence of trabeculae in vessel elements, septa in parenchyma cells, and aluminum in the G-layer of the gelatinous fiber walls, in the septa of fibers, in cambial initials and derivatives cell walls, and in the vacuole of ray cells are recorded for the first time for Melastomataceae. The results of this study indicate an additional role for gelatinous fibers in Al-accumulation, and offer a new perspective on Al-compartmentalization in the wood cells from Cerrado species.

Evolution of wood anatomical characters in Nepenthes and close relatives of Caryophyllales.

Nepenthes attracts wide attention with its spectacularly shaped carnivorous pitchers, cultural value and horticultural curiosity. Despite the plant's iconic fascination, surprisingly little anatomical detail is known about the genus beyond its modified leaf tip traps. Here, the wood anatomical diversity of Nepenthes is explored. This diversity is further assessed with a phylogenetic framework to investigate whether the wood characters within the genus are relevant from an evolutionary or ecological perspective, or rather depend on differences in developmental stages, growth habits, substrates or precipitation. Observations were performed using light microscopy and scanning electron microscopy. Ancestral states of selected wood and pith characters were reconstructed using an existing molecular phylogeny for Nepenthes and a broader Caryophyllales framework. Pairwise comparisons were assessed for possible relationships between wood anatomy and developmental stages, growth habits, substrates and ecology. Wood anatomy of Nepenthes is diffuse porous, with mainly solitary vessels showing simple, bordered perforation plates and alternate intervessel pits, fibres with distinctly bordered pits (occasionally septate), apotracheal axial parenchyma and co-occurring uni- and multiseriate rays often including silica bodies. Precipitation and growth habit (stem length) are linked with vessel density and multiseriate ray height, while soil type correlates with vessel diameter, vessel element length and maximum ray width. For Caryophyllales as a whole, silica grains, successive cambia and bordered perforation plates are the result of convergent evolution. Peculiar helical sculpturing patterns within various cell types occur uniquely within the insectivorous clade of non-core Caryophyllales. The wood anatomical variation in Nepenthes displays variation for some characters dependent on soil type, precipitation and stem length, but is largely conservative. The helical-banded fibre-sclereids that mainly occur idioblastically in pith and cortex are synapomorphic for Nepenthes , while other typical Nepenthes characters evolved convergently in different Caryophyllales lineages.

Climate trends in the wood anatomy of Acacia sensu stricto (Leguminosae: Mimosoideae).

This study investigates the structural diversity of the secondary xylem of 54 species of Acacia from four taxonomic sections collected across five climate regions along a 1200 km E-W transect from sub-tropical [approx. 1400 mm mean annual precipitation (MAP)] to arid (approx. 240 mm MAP) in New South Wales, Australia. Acacia sensu stricto ( s.s. ) is a critical group for understanding the effect of climate and phylogeny on the functional anatomy of wood. Wood samples were sectioned in transverse, tangential and radial planes for light microscopy and analysis. The wood usually has thick-walled vessels and fibres, paratracheal parenchyma and uniseriate and biseriate rays, occasionally up to four cells wide. The greater abundance of gelatinous fibres in arid and semi-arid species may have ecological significance. Prismatic crystals in chambered fibres and axial parenchyma increased in abundance in semi-arid and arid species. Whereas vessel diameter showed only a small decrease from the sub-tropical to the arid region, there was a significant 2-fold increase in vessel frequency and a consequent 3-fold decrease in the vulnerability index. Although the underlying phylogeny determines the qualitative wood structure, climate has a significant influence on the functional wood anatomy of Acacia s.s. , which is an ideal genus to study the effect of these factors.

Connection of growth and wood density with wood anatomy in downy birch grown in two different soil types

ABSTRACTSoil affects the anatomy of downy birch wood (Betula pubescens), which raises the question whether the growth of this species differs between mineral and peat soils. The aim of this study was to compare growth, density and structure of xylem of B. pubescens between trees grown in different soils. Both growth and density differed between trees grown in different soils. All measured anatomical characteristics, except double thickness of fibre walls, percentage vessel area and ray number, showed differences between the soil types: the cell dimensions were larger and numbers smaller in trees grown in mineral soil. In peat, high growth rates decreased the wall:lumen ratio of fibres in maturing wood, while no such correlation was observed in trees grown in mineral soil at any studied cambial age. In addition, axial parenchyma may have a different role in trees grown in different soils, as the rapid growth decreased and increased axial parenchyma in mineral and peat soil, respectively. The characteristics affecting wood strength were more similar between trees grown in different soils than those affecting water conductance. The observed differences between trees grown in different soils emphasise rapid growth particularly at young ages and shorter reasonable rotation period in mineral soil.

Medulloprotaxodioxylon triassicum gen. et sp. nov., a taxodiaceous conifer wood from the Norian (Triassic) of northern Bogda Mountains, northwestern China

A permineralized coniferous wood, Medulloprotaxodioxylon triassicum Wan, Yang, Tang, Liu et Wang gen. et sp. nov., is described from the Norian (Late Triassic) Huangshanjie Formation in the Dalongkou Section, Jimsar County, Xinjiang Uygur Autonomous Region, northwestern China. The fossil wood is composed of the pith, primary and secondary xylem. The pith is solid, circular, heterocellular, with numerous isolated or clustered secretory cells, and parenchyma. Secretory cells commonly form a network in a radial view. The pith is surrounded by numerous primary xylem strands and about 22 distinctive leaf traces. The primary xylem is endarch. Tracheids of primary xylem have helical and scalariform thickenings. The secondary xylem is pycnoxylic, composed of tracheids, rays and axial parenchyma. The general aspect of the tracheids and rays, presence of taxodioid cross-field pits, and abundant axial parenchyma, indicate M. triassicum can be related to the taxodiaceous Cupressaceae sensu lato. By comparison with fossil and extant species of the Cupressaceae, M. triassicum is most comparable to Sequoiadendron giganteum (Lindley) Buchholz. It is hypothesized that M. triassicum represents an ancestral form of the Sequoioideae Saxton based on the anatomical characteristics of the pith and secondary xylem. The occurrence of M. triassicum would indicate that the taxodiaceous conifers had already individualized within the Cupressaceae during the Late Triassic.