Xylem Rays Research Articles

Authentication of Harpullia arborea (Blanco) Radlk. - a traditional medicinal plant from India using microscopic techniques

Harpullia arborea (Blanco) Radlk., Sapindaceae, known as “black doll’s eyes” or “tulip tree” is a rainforest tree distributed in the tropical forests of peninsular India. Out of the 26 species of the genus, H. arborea is therapeutically more studied and widely used in folk and ayurvedic medicine. In this work, anatomical study of the leaves and stem of H. arborea was performed to provide a microscopical diagnosis for its characterization due to its increasing use in folk and ayurvedic medicine and its differentiation from other species with the same popular name. Standard light and scanning electron microscopy procedures were carried out using paradermal sections of leaf surfaces and transverse sections of lamina, midrib, and petiole. Stem preparations include longitudinal, radial and transverse sections of tertiary branches. The leaf epidermis with stellate non-glandular trichomes, cyclocytic stomata, mucilaginous cells and mesophyll without secretory sclereids, and the stem with confluent axial parenchyma, biseriate xylem rays, and the presence of rhomboidal prismatic crystals in the axial cells are the diagnostic microscopic features of the species. This structural characterization of the stem and leaf allows the identification of H.arborea, allowing certification of the authenticity of raw material.

Programmed cell death might involve in progress of wounding induced agarwood formation in stems of Aquilaria sinensis.

Agarwood, a non-timber fragrant wood, is derived from wounded Aquilaria trees (Thymelaeaceae) and is widely used in traditional medicine, incense and perfume. Agarwood-like substances and programmed cell death (PCD) can be induced by wounding signals in the suspension cells and aerial roots of Aquilaria sinensis. In this study, the dynamic process of wound-induced agarwood formation in stems of A. sinensis was observed, and the occurrence of PCD was synchronously detected using techniques such as 4',6-diamidino-2-phenylindole and dUTP nick-end labeling staining. The results showed that the wounding was a induce signal for agarwood resin formation, meanwhile might induce PCD. Interxylary phloem and xylem ray were the main sites of agarwood resin formation and PCD occurrence. There might be a relationship between the spatiotemporal pattern of PCD and agarwood resin formation: more severe PCD corresponded to a higher rate of resin formation but a shorter resin formation time; conversely, slower PCD progression corresponded to a lower rate of resin formation but a longer resin formation time. Our findings are the first to demonstrate that PCD might occur in the process of wound-induced agarwood formation at the tree level, and the spatiotemporal pattern is closely related to the formation of agarwood resin. This study provides valuable insight for further studies on the relationship between PCD and agarwood formation. HIGHLIGHTS: Programmed cell death (PCD) might occur in the process of wound-induced agarwood formation at the tree level. Interxylary phloem and xylem ray were the main sites of agarwood resin formation and PCD occurrence. Spatiotemporal pattern of PCD might have a strong impact on agarwood resin formation.

The study of the anatomical structure of Cercis siliquastrum L. leaves

Aim. To study the anatomical structure of Cercis siliquastrum L. leaves. Materials and methods. The study objects were leaves of Judas tree collected in the Botanical garden of the National University of Pharmacy in June, 2021. Micropreparations were made of fresh, dried material and fixed with a mixture of 96 % ethanol, water and glycerin (1 : 1: 1). Micropreparations were prepared and examined according to the methodsof the SPhU using a Granum microscope (Austria). A Canon PC1251 camera was used for photographing. Results and discussion. The type of the leaf blade is dorsoventral, hypostomatic, there are cells with the orange content. There are numerous stomata of anocytic (sometimes anisocytic) type. Simple multicellular hairs with a weakly warty cuticle were found on the lower and upper epidermis. A 2-3-layered collenchymatous parenchyma is located above the central vein. The bundle sheath is crystalliferous. On the xylem side, 5-6 layers of the sclerenchyma are observed. The petiole has an oval shape, slightly ribbed near the leaf blade. In the middle of the petiole there are three bundles: two radial on the sides and one central with two additional bundles. All bundles are surrounded by a common sclerenchymal ring. There are cells with the orange content in the parenchyma. On the abaxial side there is a layer of cells with calcium oxalate drusens under the sclerenchyma. The petiole is rounded, slightly ribbed. The bundle has a crescent shape in the center. The xylem rays are with the brown content. The sclerenchyma is well developed. There are drusens in the parenchyma of the petiole. Conclusions. The main anatomical features of Judas tree leaves have been determined; it will allow identifying and standardizing the plant raw material. The data obtained are necessary for the development of Drug Quality Control Methods (DQCM) for the medicinal raw material.

Tissue Structure Changes of Aquilaria sinensis Xylem after Fungus Induction

In this study, we analyzed the mechanism and the process of fungal-induced agarwood formation in Aquilaria sinensis and studied the functional changes in the xylem structure after the process. The microscopic structure of the white zone, transition zone, agarwood zone, and decay zone of 12-and 18-months of inoculation A. sinensis xylem was studied. The distribution of nuclei, starch grains, soluble sugars, sesquiterpenes, fungal propagules, and mycelium in xylem tissues was investigated by histochemical analysis. The results show that the process of agarwood formation was accompanied by apoptosis of parenchyma cells such as interxylary phloem, xylem rays, and axial parenchyma. Regular changes in the conversion of starch grains to soluble sugars, the production of sesquiterpenoids, and other characteristic components of agarwood in various types of parenchyma cells were also observed. The material transformation was concentrated in the interxylary phloem, providing a structural and material basis for the formation of agarwood. It is the core part of the production of sesquiterpenoids and other characteristic products of agarwood. Compared with the A. sinensis inoculated for 12 months, the xylem of the A. sinensis inoculated for 18 months was more vigorous. There were no significant differences between the 12 and 18 months of inoculation in terms of sugars and agarwood characteristic products. In production, harvesting after 12 months of inoculation can improve harvesting efficiency.

Anatomy and cell wall ultrastructure of sunflower stalk rind

The anatomy and ultrastructure of sunflower stalk rind are closely related to its conversion and utilization. We studied systematically the anatomy and ultrastructure of the stalk rind using light, scanning electron, transmission electron and fluorescence microscopy. The results showed that the stalk rind consisted of phloem fibers (PF), xylem fibers (XF), vessel elements (V), ground parenchyma cells (GPC), axial parenchyma cells (APC), xylem ray parenchyma cells (XRPC), and pith ray parenchyma cells (PRPC). These cell walls were divided into the middle lamella, primary wall, and secondary wall (S). It was found that the S of PF, XF and V was further divided into three layers (S1–S3), while the S of APC, GPC, XRPC and PRPC showed a non-layered cell wall organization or differentiated two (S1, S2) to seven layers (S1–S7). Our research revealed the plasmodesmata characteristics in the pit membranes (PMs) between parenchyma cells (inter-GPCs, inter-XRPCs, and inter-PRPCs). The morphology of the plasmodesmata varied with the types of parenchyma cells. The thickness and diameter of PMs between the cells (inter-Vs, V–XF, V–APC, and V–XRPC) were greater than that of PMs between parenchyma cells. The cell corners among parenchyma cells were intercellular space. The lignification degree of vessels was higher than that of parenchyma cells and fibers. The results will provide useful insights into the biological structure, conversion and utilization of sunflower stalk rind.

A petrified wood Brachyoxylon from the Lower Cretaceous of Bangoin, Tibet (Xizang), Southwest China

A new species of conifer wood, Brachyoxylon lalongense sp. nov., was discovered from the Lower Cretaceous Duoni Formation of Bangoin County in the northern part of the Lhasa Block, Southwest China. The anatomical structure of the secondary xylem is characterized by the absence of growth rings, mixed type of radial tracheary pitting, araucarioid cross-field pits, uniseriate xylem rays, and the absence of resin canals. The absence of growth rings in the secondary wood indicates that this conifer was evergreen and the area was dominated by a hot climate during the Early Cretaceous. This conclusion is coincident with the coeval palaeobotanical and palynological evidences discovered in Tibet.

Development of successive cambia and structure of secondary xylem in the stems and roots of Distimake tuberosus (Convolvulaceae)

In the present study, development of trilobed stem is investigated in Distimake tuberosus (Convolvulaceae) by histological methods. Increase in stem thickness and formation of trilobed stem was achieved by forming crescent shaped successive cambial segments from the pericyclic parenchyma at three equidistant sites. In contrast, the alternate segments of the vascular cambium were functionally less active, dividing leisurely (referred henceforth as functionally less active cambium) and did not form the successive cambium. The newly formed cambial segments divide bi-directionally and produced its derivatives, while functionally less active segment lagged behind. The secondary xylem formed from the functionally less active cambial segments have unique pattern of vessels distribution i.e., wide vessels rare or completely absent. Parenchyma (both, axial and ray) proliferation, formation of ray cambium, functionally inverse cambia, tyloses in fibriform vessels and the occurrence of bordered pits in xylem ray cells are observed in all samples. Root diameter increased by developing concentric rings of successive cambia and maintained a circular outline. Formation of successive cambia on three sides and alteration in stem outline may be associated with protection of conducting elements against stem torsion and internal injury. Formation of conducting elements from the ray cambium and internal cambium suggest rapid and safe conduction of photosynthate, water and mineral elements.

In Planta Analysis of the Radial Movement of Minerals from Inside to Outside in the Trunks of Standing Japanese Cedar (Cryptomeria japonica D. Don) Trees at the Cellular Level

Although the radial movement of minerals in tree trunks is a widely accepted phenomenon, experimental evidence of their movement in standing trees and underlying mechanisms is very limited. Previously, we clarified that cesium (Cs) artificially injected into the outer part of the sapwood of standing Japanese cedar (Cryptomeria japonica D. Don) trunks moved to the inner part of the sapwood, including the intermediate wood, via active transport by xylem parenchyma cells and diffusion through cell walls and then moved into the heartwood by diffusion. To understand the mechanism underlying the radial movement of minerals in the standing tree trunk, it is necessary to clarify their movement in the opposite direction. Therefore, the present study aimed to determine the radial movement of minerals from inside to outside in the trunks of standing trees at the cellular level. For this, a long hole across the center part of the trunk, which reached the heartwood, intermediate wood, and sapwood, was made in standing Japanese cedar trunks, and a solution of stable isotope Cs was continuously injected into the hole for several days as a tracer. The injected part of the trunk was collected after being freeze-fixed with liquid nitrogen, and the frozen sample was subjected to analysis of Cs distribution at the cellular level using cryo-scanning electron microscopy/energy-dispersive X-ray spectroscopy. The Cs injected into the inner sapwood or intermediate wood rapidly moved toward the outer sapwood via xylem ray parenchyma cells together with diffusion through the cell walls. In contrast, the Cs injected into the heartwood barely moved to the sapwood, although it reached a part of the inner intermediate wood. These results suggest that minerals in xylem ray parenchyma cells in the sapwood are bidirectionally supplied to each other; however, the minerals accumulated in the heartwood may not be supplied to living cells.

Pharmacognostical and Phytochemical Analysis of Stems of Vitex pinnata Linn.

Background and Objective: Vitex pinnata Linn. (Syn: Vitex pubescens Vahl.) is a moderately sized tree of tropical Asia. Vitex pinnata is a tree with trifoliate leaves, grey to brown bark. The leaves and stems are potential as an antioxidant, because of flavonoids, alkaloids and terpenoids constituents. The present study aimed to establish the pharmacognostic features of leaf, stem and powdered stem material and quality parameters including physicochemical evaluation. Materials and Methods: The leave and stems were investigated, which comprised macroscopic and microscopic assessment, phytochemical screening and physicochemical characterization of the stems, besides the microscopic analysis of the powder. All photographs of different magnifications were taken using a digital camera attached to the Nikon Labphot 2 Microscopic Unit. Results: The microscopical studies of stem and powders of Vitex pinnata revealed the presence of cortex, periderm, sclerenchyma, secondary phloem, vessels, xylem fibres, xylem rays, collapsed phloem cells, phellem, sclereids, phloem ray, sieve element, starch grains, prismatic calcium oxalate crystals and vessel elements, etc. Phytochemical screening revealed the presence of flavonoids, saponins, triterpenes and steroids in the crude extract. The values of the physicochemical parameters such as loss on drying 4.12%, foreign organic matter 5.60%, total Ash 09.43%, acid insoluble ash 2.34%, water-soluble Ash 3.04%, sulphated ash 3.20%, alcohol soluble extractives 15.6% and water-soluble extractives 16.8%, respectively. Conclusion: The information obtained with botanical, physicochemical and phytochemical studies could be used to identify Vitex pinnata and to certify the authenticity of commercial samples to effectively contribute to quality control of that vegetable raw material.

Anatomical characteristics of fossil wood collected from the Manchar Formation (Miocene), Thano Bula Khan, Sindh, Pakistan

The characterization of petrified wood provides valuable information about paleoclimatology and geological history and helps to reconstruct the past forest flora of different parts of the earth. The present study was undertaken to evaluate the anatomical characteristics of fossil wood of the Miocene age collected from the Manchar Formation exposed at Thano Bula Khan, Sindh, Pakistan. In order to carry out a detailed anatomical investigation, three-dimensional sections were prepared using a petrotome. The microscopic analysis allowed us to study vessel size and arrangement, wood parenchyma, fibers, and xylem rays. Based on the comparison between recent and fossil wood, we concluded that the investigated characters are comparable with those of the genus Atalantia Corrêa of the Rutaceae family. Therefore, it was named as Atalantioxylon thanobolensis sp. nov. with reference to the location of Thano Bula Khan from which the fossil wood was collected.

Activity of Stem-Injected and Soil Applied Imidacloprid Against Hemlock Woolly Adelgid in the Great Smoky Mountains

Eastern hemlock (Tsuga canadensis [L.] Carrière) is an important component of the riparian ecosystem. Due to the widespread establishment of hemlock woolly adelgid (Adelges tsugae Annand)(HWA) across the range of eastern hemlock, woodland trees may be infested for extended periods (years), resulting in their decline. Imidacloprid, a systemic neonicotinoid insecticide, may be used as a strategy in forested settings to manage HWA while more long-term solutions become established, such as biological controls. Symptoms of prolonged infestation include extensive dieback and thinned canopies. In this study, trees with a diameter at breast height (DBH) of 24.7 ± 2.7 SD cm in poor condition were treated with imidacloprid. Trees were treated once by trunk-injection (IMA-jet) or by soil drench in the Greenbrier area of the Great Smoky Mountains National Park, Gatlinburg, TN, USA. Changes in tree growth and HWA density were measured for 3 consecutive years. Imidacloprid-treated trees recovered, whereas the untreated trees declined. Imidacloprid treatments resulted in significantly higher 3-year mean percent growth (65.6% to 71.7% of tips) compared to the untreated controls (10.5% of tips). HWA density 3-year means in the imidacloprid-treated trees (0.10 to 1.09 per cm) likewise were statistically different to the untreated trees (2.72 per cm). The extended activity of imidacloprid-treated hemlock was attributed to storage in the symplast (xylem ray parenchyma) and to perennial needle retention. This study demonstrates that trunk-injection with IMA-jet is effective against HWA and comparable with soil drench to protect trees in the long term (≥ 4 years).

Chloroplast Distribution in the Stems of 23 Eucalypt Species.

Small diameter branchlets and smooth barked stems and branches of most woody plants have chloroplasts. While the stems of several eucalypt species have been shown to photosynthesise, the distribution of chloroplasts has not been investigated in detail. The distribution of chloroplasts in branchlets (23 species) and larger diameter stems and branches with smooth bark (14 species) was investigated in a wide range of eucalypts (species of Angophora, Corymbia and Eucalyptus) using fresh hand sections and a combination of bright field and fluorescence microscopy. All species had abundant stem chloroplasts. In both small and large diameter stems, the greatest concentration of chloroplasts was in a narrow band (usually 100–300 μm thick) immediately beneath the epidermis or phellem. Deeper chloroplasts were present but at a lower density due to abundant fibres and sclereids. In general, chloroplasts were found at greater depths in small diameter stems, often being present in the secondary xylem rays and the pith. The cells of the chlorenchyma band were small, rounded and densely packed, and unlike leaf mesophyll. A high density of chloroplasts was found just beneath the phellem of large diameter stems. These trees gave no external indication that green tissues were present just below the phellem. In these species, a thick phellem was not present to protect the inner living bark. Along with the chlorenchyma, the outer bark also had a high density of fibres and sclereids. These sclerenchyma cells probably disrupted a greater abundance and a more organised arrangement of the cells containing chloroplasts. This shows a possible trade-off between photosynthesis and the typical bark functions of protection and mechanical strength.

The Spatio-Temporal Distribution of Cell Wall-Associated Glycoproteins During Wood Formation in Populus.

Plant cell wall associated hydroxyproline-rich glycoproteins (HRGPs) are involved in several aspects of plant growth and development, including wood formation in trees. HRGPs such as arabinogalactan-proteins (AGPs), extensins (EXTs), and proline rich proteins (PRPs) are important for the development and architecture of plant cell walls. Analysis of publicly available gene expression data revealed that many HRGP encoding genes show tight spatio-temporal expression patterns in the developing wood of Populus that are indicative of specific functions during wood formation. Similar results were obtained for the expression of glycosyl transferases putatively involved in HRGP glycosylation. In situ immunolabelling of transverse wood sections using AGP and EXT antibodies revealed the cell type specificity of different epitopes. In mature wood AGP epitopes were located in xylem ray cell walls, whereas EXT epitopes were specifically observed between neighboring xylem vessels, and on the ray cell side of the vessel walls, likely in association with pits. Molecular mass and glycan analysis of AGPs and EXTs in phloem/cambium, developing xylem, and mature xylem revealed clear differences in glycan structures and size between the tissues. Separation of AGPs by agarose gel electrophoresis and staining with β-D-glucosyl Yariv confirmed the presence of different AGP populations in phloem/cambium and xylem. These results reveal the diverse changes in HRGP-related processes that occur during wood formation at the gene expression and HRGP glycan biosynthesis levels, and relate HRGPs and glycosylation processes to the developmental processes of wood formation.

Xylella fastidiosa causes transcriptional shifts that precede tylose formation and starch depletion in xylem.

Pierce's disease (PD) in grapevine (Vitis vinifera) is caused by the bacterial pathogen Xylella fastidiosa. X. fastidiosa is limited to the xylem tissue and following infection induces extensive plant‐derived xylem blockages, primarily in the form of tyloses. Tylose‐mediated vessel occlusions are a hallmark of PD, particularly in susceptible V. vinifera. We temporally monitored tylose development over the course of the disease to link symptom severity to the level of tylose occlusion and the presence/absence of the bacterial pathogen at fine‐scale resolution. The majority of vessels containing tyloses were devoid of bacterial cells, indicating that direct, localized perception of X. fastidiosa was not a primary cause of tylose formation. In addition, we used X‐ray computed microtomography and machine‐learning to determine that X. fastidiosa induces significant starch depletion in xylem ray parenchyma cells. This suggests that a signalling mechanism emanating from the vessels colonized by bacteria enables a systemic response to X. fastidiosa infection. To understand the transcriptional changes underlying these phenotypes, we integrated global transcriptomics into the phenotypes we tracked over the disease spectrum. Differential gene expression analysis revealed that considerable transcriptomic reprogramming occurred during early PD before symptom appearance. Specifically, we determined that many genes associated with tylose formation (ethylene signalling and cell wall biogenesis) and drought stress were up‐regulated during both Phase I and Phase II of PD. On the contrary, several genes related to photosynthesis and carbon fixation were down‐regulated during both phases. These responses correlate with significant starch depletion observed in ray cells and tylose synthesis in vessels.

Microscopic Investigations and Pharmacognosy of Striga orobanchioides Benth

Objective: To study delineate Pharmacognosy of the stem of plant Striga Orobanchioides Benth (Scrophulariaceae), prime plant in Indian system of medicine. A comprehensive account on standardization of herbal drug Striga Orobanchioides Benth by using microscopic as well as Pharmacognostic parameters. In the field of herbal medicines, the main issues are quality, purity, and effectiveness, as in many cases herbal drugs are knowingly or unknowingly substituted or adulterated with similar species or varieties. Methods: The macroscopy, microscopy, physicochemical analysis, preliminary phytochemical testing of the powder of plant stem and other WHO recommended methods for standardization was done. Results: T S of young as well as old stem was studied. T.S. of the young stem confirmed the presence of thin epidermal layer, fairly wide cortex and thin vascular cylinder having the pith disintegrated or retained as homogeneous parenchymatous tissue. T.S. of the old stem confirmed the presence of cortical cells, parenchyma cells, sclerenchyma cells, vascular tissue. The lower conical part of the stem has epidermis cortical zone and vascular cylinder continued from its wide upper part. The cortical zone consists of parenchymatous ground tissue with sealed masses of sclerenchyma cells. The xylem tissue becomes gradually narrow and thin in the end of the stem. It includes compact radial lines of vessels, filnes and xylem rays. Conclusion: The above parameters, being reported to the first time for the studied plant species, and are significant towards establishing the microscopic and Pharmacognostic standards for future identification and authentication of genuine herbal drug. It can be concluded that the Pharmacognostic outline of Striga Orobanchioides plant is beneficial in developing standards for quality, purity and sample identification.

New records of Early Cretaceous petrified wood in Yumen, northwestern Gansu Province, China and their palaeoclimatic implications

Several fossil woods from Early Cretaceous sediments in Yumen City in northwestern North China Block, China, have been described. They belong to two fossil wood taxa, Piceoxylon yumeniense Zhou, Peng, Deng, Zhang and Yang n. sp. and Protophyllocladoxylon chijinense Zhou, Peng, Deng, Zhang and Yang n. sp. The well-preserved specimens yield secondary xylem with distinct growth rings. Piceoxylon yumeniense exhibits cross-field with taxodioid pits as well as two distinct xylem ray types. The bi- to triseriate rays are characterised by one or two horizontal resin canals with unequal uniseriate ends. Protophyllocladoxylon chijinense Zhou, Peng, Deng, Zhang and Yang n. sp. shows window-like cross-field pits, which are occasionally cupressoid and have uniseriate xylem rays. These fossil wood records improve our understanding of the fossil diversity, floral composition and palaeoclimate of the Xiagou Formation. Palaeoclimatic analysis of the palaeoxylogical assemblage indicates that the northwestern Gansu region predominantly exhibited a warm and wet climate condition, while a brief cooling event may have occurred in the region during the Early Cretaceous.

Microscopic histochemical comparison during mountain-agarwood formation

Mountain-agarwood plays an important role in ethnic medicine in China for its pharmaceutical value. Modern pharmacological researches demonstrated that mountain-agarwood was effective for its anti-myocardial ischemia, antibacterial, anti-inflammatory, antitumor and analgesic effects. Mountain-agarwood derives from the peeled roots, stems or twigs of Syringa pinnatifolia which belongs to Syringa genus. It often depends on the purple substance and fragrance to estimate the formation of mountain-agarwood. However, the mechanism of mountain-agarwood formation has not been reported. To observe the microcosmic change in the process during the formation of mountain-agarwood, this study described the microscopic and histochemical characteristics of mountain-agarwood formation through histochemical staining. Our results showed that a significant difference of the distribution of tyloses existed during mountain-agarwood formation. It was observed that inchoate mountain-agarwood had more starch granules and viable cells than mountain-agarwood formed with high level or low level. The amount of polysaccharide and degree of lignification were increased during the mountain-agarwood formation. The results indicated that the mountain-agarwood, which meets the quality requirements for pharmaceutical use, contained the following characteristics: a large amount of purple tyloses in heartwood; yellow-brown tyloses distributing in heartwood and sapwood which were less in the latter; lignification with high level; a few viable cells; lots of polysaccharide and few starch granules in xylem rays cell. This study is aimed to reveal the change of histochemical characteristics during mountain-agarwood formation, and lay the foundation for exploring the mechanism of mountain-agarwood formation.

The impact of natural and artificial weathering on the anatomy of selected tropical hardwoods

Abstract The effect of natural and artificial weathering on the anatomy of seven tropical hardwoods: Bangkirai (Shorea obtusa Wall.), Cumaru (Dipteryx odorata (Aubl.) Wild.), Cumaru Rosa (Dipteryx magnifica (Ducke) Ducke), Ipé (Tabebuia serratifolia Nichols.), Jatobá (Hymenaea courbaril L.), Kusia (Nauclea diderrichii Merill) and Massaranduba (Manilkara bidentata A. Chev.), was studied. As a result of weathering some characteristic anatomical changes occurred: the weakening of connections between cell elements related to the degradation of the middle lamella; micro-cracks in cell walls; total degradation of parenchyma cells in xylem rays, or significant thinning of parenchyma cell walls and their extreme shrinkage; micro-cracks in the vicinity of xylem rays; significant transversal disruptions in libriform fibres; ablation of pit membranes in vessels and parenchyma cells; changes in the secondary wall of libriform fibres, for example, their defibrillation and weathering-degradation of the S1 layer; and spherical formations on the S3 layer of cell walls produced from condensing compounds of degraded lignin and hemicelluloses as well as thermo-mechanical wrinkling. The highest incidence of micro-cracks after both modes of weathering was found in the densest species; Cumaru, Ipé, and Massaranduba.

Cambial Variants Combine Successive Cambia and Intraxylary Phloem in Convolvulaceae in Taiwan

Secondary stem growth develops different cambial variants in Convolvulaceae. Here, the cambial variant features of 17 species in seven genera (Convolvulaceae) in Taiwan are presented. The xylem rings produce various successive cambial types and the primary xylem and intraxylary phloem are produced in the outer and inner pith, respectively. The two Argyreia species have round or elliptical stems with continuous secondary xylem and phloem rings. In the eight Ipomoea species, secondary growth has two to four layers of successive cambia and xylem, dispersed with parenchyma tissue, except for I. nil and I. violacea with one layer of successive cambia. The first secondary xylem segments are separated by few or many xylem rays: I. cairica and I. obscura have three to five xylem rays and I. triloba has numerous xylem rays. The first secondary xylem of Erycibe henryi is divided by numerous rays in small stems, but develops more layers, as adjacent segments separated by xylem rays, in larger stems. Owing to continuous vascular bundle division, it has a dissected xylem. The secondary growth of Distimate tuberosa and Operculina turpethum produces two layers of successive cambia; the secondary successive cambium is divided evenly by rays into many arcs/segments. The stem thickness of I. pes-caprae subsp. brasiliensis increases via concentric successive cambia. Owing to shallowly lobed stems with directional successive cambia, I. obscura and I. triloba stems are irregularly shaped. I. littoralis and Stictocardia tilifolia stems are triangular without directional successive cambia. I. hederifolia and Merremia gemella stems have two to three deep lobes. Parenchyma proliferation results in thicker cortex with mucilaginous canals. The xylem vessels are dispersed and diffuse-porous; the vasicentric paratracheal parenchyma around them is common to all species. A bracketed key was developed comparing the secondary xylem structures of the 17 species, providing a basis for further morphological studies.

A new species of Barleria (Acanthaceae), its morphotaxonomy, cytogenetics and phylogenetic placement

A new species, Barleria lavaniana (Acanthaceae), is described and illustrated. It resembles B. longiflora but differs from it in the characters of calyx, stamen, style and stigma. Stem anatomy reveals that vessel elements are mostly angular with a short tail at one end and a long tail on the other end. Xylem rays are usually biseriate and xylem fibres relatively thin-walled. Interxylary phloem is generally characterized by a single companion cell. The somatic chromosome number was 2n = 2x = 40. The karyotype is moderately symmetrical and fell in Stebbins’ 3b category. Chromosomes have median and submedian region centromeres. Based on cpDNA data, the new species is placed in subgenus Barleria and shows phylogenetic affinity towards B. longiflora and B. acuminata. Our findings suggest the need for comprehensive phylogenetic analyses of the genus Barleria based on high-throughput sequencing data to understand species interrelationships and biogeography.