Endodermal Cell Walls Research Articles

Root cell wall polysaccharides and endodermal barriers restrict long-distance Cd translocation in the roots of Kentucky bluegrass

Soil Cd pollution is a significant environmental issue faced by contemporary society. Kentucky bluegrass is considered a potential phytoremediation species, as some varieties have excellent cadmium (Cd) tolerance. However, the mechanisms of Cd accumulation and transportation in Kentucky bluegrass are still not fully understood. The Cd-tolerant Kentucky bluegrass cultivar ‘Midnight’ (M) exhibits lower Cd translocation efficiency and a higher leaf Cd concentration compared to the Cd-sensitive cultivar ‘Rugby II’ (R). We hypothesized that Cd translocation from roots to shoots in cultivar M is hindered by the endodermal barriers and cell wall polysaccharides; hence, we conducted Cd distribution, cytological observation, cell wall component, and transcriptomic analyses under Cd stress conditions using the M and R cultivars. Cd stress resulted in the thickening of the endodermis and increased synthesis of cell wall polysaccharides in both the M and R cultivars. Endodermis development restricted the radical transport of Cd from the root cortex to the stele, while the accumulation of cell wall polysaccharides promoted the binding of Cd to the cell wall. These changes further inhibited the long-distance translocation of Cd from the roots to the aerial parts. Furthermore, the M cultivar exhibited limited long-distance Cd translocation efficiency compared to the R cultivar, which was attributed to the enhanced development of endodermal barriers and increased Cd binding by cell wall polysaccharides. This study provides valuable insights for screening high Cd transport efficiency in Kentucky bluegrass based on anatomical structure and genetic modification.

The Arabidopsis SGN3/GSO1 receptor kinase integrates soil nitrogen status into shoot development

The Casparian strip is a barrier in the endodermal cell walls of plants that allows the selective uptake of nutrients and water. In the model plant Arabidopsis thaliana, its development and establishment are under the control of a receptor-ligand mechanism termed the Schengen pathway. This pathway facilitates barrier formation and activates downstream compensatory responses in case of dysfunction. However, due to a very tight functional association with the Casparian strip, other potential signaling functions of the Schengen pathway remain obscure. In this work, we created a MYB36-dependent synthetic positive feedback loop that drives Casparian strip formation independently of Schengen-induced signaling. We evaluated this by subjecting plants in which the Schengen pathway has been uncoupled from barrier formation, as well as a number of established barrier-mutant plants, to agar-based and soil conditions that mimic agricultural settings. Under the latter conditions, the Schengen pathway is necessary for the establishment of nitrogen-deficiency responses in shoots. These data highlight Schengen signaling as an essential hub for the adaptive integration of signaling from the rhizosphere to aboveground tissues.

Deposition of silica in sorghum root endodermis modifies the chemistry of associated lignin.

Silica aggregates at the endodermis of sorghum roots. Aggregation follows a spotted pattern of locally deposited lignin at the inner tangential cell walls. Autofluorescence microscopy suggests that non-silicified (-Si) lignin spots are composed of two distinct concentric regions of varied composition. To highlight variations in lignin chemistry, we used Raman microspectroscopy to map the endodermal cell wall and silica aggregation sites in sorghum roots grown hydroponically with or without Si amendment. In +Si samples, the aggregate center was characterized by typical lignin monomer bands surrounded by lignin with a low level of polymerization. Farther from the spot, polysaccharide concentration increased and soluble silicic acid was detected in addition to silica bands. In -Si samples, the main band at the spot center was assigned to lignin radicals and highly polymerized lignin. Both +Si and -Si loci were enriched by aromatic carbonyls. We propose that at silica aggregation sites, carbonyl rich lignin monomers are locally exported to the apoplast. These monomers are radicalized and polymerized into short lignin polymers. In the presence of silicic acid, bonds typically involved in lignin extension, bind to silanols and nucleate silica aggregates near the monomer extrusion loci. This process inhibits further polymerization of lignin. In -Si samples, the monomers diffuse farther in the wall and crosslink with cell wall polymers, forming a ring of dense lignified cell wall around their export sites.

Trichoderma-secreted anthranilic acid promotes lateral root development via auxin signaling and RBOHF-induced endodermal cell wall remodeling

Trichoderma spp. have evolved the capacity to communicate with plants by producing various secondary metabolites (SMs). Nonhormonal SMs play important roles in plant root development, while specific SMs from rhizosphere microbes and their underlying mechanisms to control plant root branching are still largely unknown. In this study, a compound, anthranilic acid (2-AA), is identified from T.guizhouense NJAU4742 to promote lateral root development. Further studies demonstrate that 2-AA positively regulates auxin signaling and transport in the canonical auxin pathway. 2-AA also partly rescues the lateral root numbers of CASP1pro:shy2-2, which regulates endodermal cell wall remodeling via an RBOHF-induced reactive oxygen species burst. In addition, our work reports another role for microbial 2-AA in the regulation of lateral root development, which is different from its better-known role in plant indole-3-acetic acid biosynthesis. In summary, this study identifies 2-AA from T.guizhouense NJAU4742, which plays versatile roles in regulating plant root development.

Frozen mountain pine needles: The endodermis discriminates between the ice-containing central tissue and the ice-free fully functional mesophyll.

Conifer (Pinaceae) needles are the most frost-hardy leaves. During needle freezing, the exceptional leaf anatomy, where an endodermis separates the mesophyll from the vascular tissue, could have consequences for ice management and photosynthesis. The eco-physiological importance of needle freezing behaviour was evaluated based on the measured natural freezing strain at the alpine treeline. Ice localization and cellular responses to ice were investigated in mountain pine needles by cryo-microscopic techniques. Their consequences for photosynthetic activity were assessed by gas exchange measurements. The freezing response was related to the microchemistry of cell walls investigated by Raman microscopy. In frozen needles, ice was confined to the central vascular cylinder bordered by the endodermis. The endodermal cell walls were lignified. In the ice-free mesophyll, cells showed no freeze-dehydration and were found photosynthetically active. Mesophyll cells had lignified tangential cell walls, which adds rigidity. Ice barriers in mountain pine needles seem to be realised by a specific lignification patterning of cell walls. This, additionally, impedes freeze-dehydration of mesophyll cells and enables gas exchange of frozen needles. At the treeline, where freezing is a dominant environmental factor, the elaborate needle freezing pattern appears of ecological importance. This article is protected by copyright. All rights reserved.

Advances in the development and function of plant root endodermis

<p indent="0mm">Root, an important underground vegetative organ of plants, plays diversified roles in plant lifecycle, including fixation and support, absorption and transportation, storage and reproduction. In meristem zone of root tip, the apical meristem is continuously divided to produce new cells, promoting the growth of root tip. Mature tissues formed through primary growth constituted the primary structure of plant roots. Water and mineral ions entered the epidermis of root, passed through the outer cortex, cortex, and endodermis in a radial direction, and reached the middle column, and were transported upward in xylem through transpiration, so as to meet the needs of aboveground part. The endodermis lies the innermost cortex surrounding the central vascular tissue system, as is constructed by only monolayer cells Endodermis is a cylindrical boundary separating the central vascular tissue from the outer cortex, and is an extracellular barrier for plant selective nutrient absorption. There were mainly two stages in differentiation of endodermis, of which in differentiation stage I, lignin was continuously deposited on lateral and radial walls of endodermis cells near the root tip, forming Casparian strips. The nature of Casparian strips was a local modification on the primary wall of endodermal layer, which was formed by the lignin polymer “impregnate” the primary wall. The complete Casparian strips show a continuous belt thickening structure, which blocked the apoplast transport pathway, prevented the diffusion of solutes between cell walls, and forced solutes to transport through the plasma membrane. In differentiation stage II, and based on the Casparian strips, hydrophobic suberin was deposited on six cell walls of endodermal cells, forming suberin lamellae structure, which inhibited the transmembrane transport of substances and was a protective barrier structure. Development of Casparian strips and suberin lamellae structure are regulated by their own growth and development mechanism and closely regulated by external environmental factors. The structure of endodermis could respond to the stress environment, and the lack of necessary mineral elements, including potassium, iron or sulfur, may cause changes in composition and structure of the Casparian strips and suberin lamellae. The above change was called plant phenotypic plasticity, whose most significant function was to support plants to adapt to the environment, integrate environmental information, optimize nutrient absorption, and maintain ion homeostasis in plants, so as to improve their survival under stressful environment. A complete suberin lamellae barrier was capable of preventing calcium ions from flowing in and potassium ions from seeping out, maintaining the balance of calcium/potassium ions in plants, supporting to regulate calcium signaling system, promoting plants photosynthesis, and improving stress resistance of crops. The paper comprehensively introduced the general development mode of plant endodermis, and the structure, concluded the composition and formation regulation mechanism of Casparian strips and suberin lamellae, and discussed the changing law of endodermis plasticity responding to abiotic stress and its importance for maintaining plant ion homeostasis, as well as prospected the future research direction, providing a new idea for cultivating new stress-resistant species.

Root cell wall remodeling mediates copper oxide nanoparticles phytotoxicity on lettuce (Lactuca sativa L.)

Root cell wall (RCW) remodeling induced by copper oxide nanoparticles (CuO NPs) and its consequences for root growth of lettuce (Lactuca sativa L.) were investigated in this study. The results showed that a low concentration of CuO NPs (5 mg L−1) stimulated reactive oxygen species (ROS) signaling, led to the degradation of pectin by H2O2, and promoted root elongation by 22.1% by triggering RCW loosening. However, under treatment with a high concentration of CuO NPs (450 mg L−1), the unordered distribution of pectin homogalacturonan enhanced cell wall adhesion. Also, the increased xyloglucan and the decreased xyloglucan endotransglycosylase/hydrolase (XTH) activities caused cell wall stiffening, making it difficult for lettuce roots to extend. Meanwhile, the contents of hemicellulose and low-methylated pectin were increased remarkably due to the downregulation of the encoding genes XTH15, XTH17, XTH31 and the upregulation of PME3, which provided abundant binding sites of RCW with CuO NPs. In addition, the accelerated development of the apoplastic barrier and root lignification blocked the absorption of CuO NPs, and the endodermal cell walls were doubled in thickness, greatly enhancing their retention capacity to CuO NPs. Taken together, the above findings suggest that CuO NPs have concentration-dependent effects on lettuce roots, which are associated with plant tolerance and mediated by RCW remodeling.

Transcriptional networks regulating suberin and lignin in endodermis link development and ABA response.

Vascular tissues are surrounded by an apoplastic barrier formed by endodermis that is vital for selective absorption of water and nutrients. Lignification and suberization of endodermal cell walls are fundamental processes in establishing the apoplastic barrier. Endodermal suberization in Arabidopsis (Arabidopsis thaliana) roots is presumed to be the integration of developmental regulation and stress responses. In root endodermis, the suberization level is enhanced when the Casparian strip, the lignified structure, is defective. However, it is not entirely clear how lignification and suberization interplay and how they interact with stress signaling. Here, in Arabidopsis, we constructed a hierarchical network mediated by SHORT-ROOT (SHR), a master regulator of endodermal development, and identified 13 key MYB transcription factors (TFs) that form multiple sub-networks. Combined with functional analyses, we further uncovered MYB TFs that mediate feedback or feed-forward loops, thus balancing lignification and suberization in Arabidopsis roots. In addition, sub-networks comprising nine MYB TFs were identified that interact with abscisic acid signaling to integrate stress response and root development. Our data provide insights into the mechanisms that enhance plant adaptation to changing environments.

Histochemical Staining of Suberin in Plant Roots.

Histological stains are useful tools for characterizing cell shape, arrangement and the material they are made from. Stains can be used individually or simultaneously to mark different cell structures or polymers within the same cells, and to visualize them in different colors. Histological stains can be combined with genetically-encoded fluorescent proteins, which are useful for understanding of plant development. To visualize suberin lamellae by fluorescent microscopy, we improved a histological staining procedure with the dyes Fluorol Yellow 088 and aniline blue. In the complex plant organs such as roots, suberin lamellae are deposited deep within the root on the endodermal cell wall. Our procedure yields reliable and detailed images that can be used to determine the suberin pattern in root cells. The main advantage of this protocol is its efficiency, the detailed visualization of suberin localization it generates in the root, and the possibility of returning to the confocal images to analyze and re-evaluate data if necessary.

Nitrogen depletion enhances endodermal suberization without restricting transporter-mediated root [formula omitted] influx

Roots vary their permeability to aid radial transport of solutes towards xylem vessels in response to nutritional cues. Nitrogen (N) depletion was previously shown to induce early suberization of endodermal cell walls and reduce hydraulic conductivity of barley roots suggesting reduced apoplastic transport of ions (Armand et al., 2019). Suberization may also limit transcellular ion movement by blocking access to transporters (Barberon et al., 2016). The aim of this study was to confirm that N depletion induced suberization in the roots of barley and demonstrate that this was a specific effect in response to NO3− depletion. Furthermore, in roots with early and enhanced suberization, we assessed their ability for transporter-mediated NO3− influx. N depletion induced lateral root elongation and early and enhanced endodermal suberization of the seminal root of each genotype. Both root to shoot NO3− translocation and net N uptake was half that of plants supplied with steady-state NO3−. Genes with predicted functions in suberin synthesis (HvHORST) and NO3− transport (HvNRT2.2) were induced under N-deplete conditions. N-deplete roots had a higher capacity for high-affinity NO3− influx in early suberized roots than under optimal NO3−. In conclusion, NO3− depletion induced early and enhanced suberization in the roots of barley, however, suberization did not restrict transcellular NO3− transport.

Aliphatic suberin confers salt tolerance to Arabidopsis by limiting Na+ influx, K+ efflux and water backflow

Uncontrolled uptake of Na+ is the reason that many species are sensitive to salinity. Suberin is a protective barrier found in the walls of root endodermal cells that appears to be important for salt tolerance, yet its specific protective mechanism has not been fully elucidated. Here we investigated the role of aliphatic suberin in protecting plants against salt stress by using a mutant of Arabidopsis, cyp86a1, which exhibits a significant reduction of root aliphatic suberin. We found that NaCl significantly increased suberization in roots of hydroponic-grown wild-type plants, but not in cyp86a1. Cyp86a1 exhibited a salt-sensitive phenotype. Compared with wild-type, Na+ accumulation in shoots was higher in cyp86a1. We provide evidence that increased Na+ uptake was via the root transcellular pathway. Furthermore, cyp86a1 accumulated less K+ in shoots than wild-type under NaCl stress, which was a consequence of increased K+ efflux from the root vasculature. Additionally, we provide evidence that aliphatic suberin reduces inflow of water across the root endodermis under non-stress conditions but reduces the backflow of water to the medium under salt stress. Finally, we propose a model for the role of aliphatic suberin in restricting Na+ influx, K+ efflux and water backflow in plants under saline conditions.

Silicification of Root Tissues.

Silicon (Si) is not considered an essential element, however, its tissue concentration can exceed that of many essential elements in several evolutionary distant plant species. Roots take up Si using Si transporters and then translocate it to aboveground organs. In some plant species, root tissues are also places where a high accumulation of Si can be found. Three basic modes of Si deposition in roots have been identified so far: (1) impregnation of endodermal cell walls (e.g., in cereals, such as Triticum (wheat)); (2) formation of Si-aggregates associated with endodermal cell walls (in the Andropogoneae family, which includes Sorghum and Saccharum (sugarcane)); (3) formation of Si aggregates in “stegmata” cells, which form a sheath around sclerenchyma fibers e.g., in some palm species (Phoenix (date palm)). In addition to these three major and most studied modes of Si deposition in roots, there are also less-known locations, such as deposits in xylem cells and intercellular deposits. In our research, the ontogenesis of individual root cells that accumulate Si is discussed. The documented and expected roles of Si deposition in the root is outlined mostly as a reaction of plants to abiotic and biotic stresses.

The Effect of Cadmium on the Activity of Stress-Related Enzymes and the Ultrastructure of Pea Roots.

The analysis of the effects of cadmium (Cd) on plant cells is crucial to understand defense mechanisms and adaptation strategies of plants against Cd toxicity. In this study, we examined stress-related enzyme activities after one and seven days of Cd application and the ultrastructure of roots of Pisum sativum L. after seven days of Cd treatment (10, 50, 100, and 200 μM CdSO4). Our results showed that phenylalanine ammonia-lyase (PAL) activity and the amount of Cd accumulated in the roots were significantly positively correlated with the Cd concentration used in our experiment. However, Cd caused a decrease of all studied antioxidative enzyme activities (i.e., catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX)). The analysis of the ultrastructure (TEM) showed various responses to Cd, depending on Cd concentrations. In general, lower Cd concentrations (50 and 100 μM CdSO4) mostly resulted in increased amounts of oil bodies, plastolysomes and the accumulation of starch granules in plastids. Meanwhile, roots treated with a higher concentration of Cd (200 μM CdSO4) additionally triggered protective responses such as an increased deposition of suberin lamellae in the endodermal cell walls. This indicates that Cd induces a complex defense response in root tissues.

Silicon increases cell wall thickening and lignification in rice (Oryza sativa) root tip under excess Fe nutrition

Iron (Fe) as a micronutrients and silicon (Si) as a cell wall element are important in plant cell wall extension and integrity. While the interaction of exogenous Si and excess Fe on root cell wall modifications is known, the effects of these nutritional parameters on the spatial changes in the activities of genes and/or enzymes involved in the lignification of root cell walls are not well studied. Thus, these parameters were investigated in the root apical part (AP) and basal part (BP) of rice (Oryza sativa L.) plants supplied with and without Si (1.5 mM) under normal (10 mg/L) and excess Fe (150 mg/L) nutrition for 7 days. Beside growth retardation, excess Fe increased the activities of phenylalanine ammonia lyase (PAL), superoxide dismutase and NADPH–oxidase and PAL and cell wall peroxidase (POD) genes expression, along with the increased phenols and H2O2 contents in the root AP. Furthermore, the increased thickening of endodermal, exodermal and metaxylem cell walls in the root AP by excess Fe was attributed to the enhanced POD activity. POD expression, endodermal and exodermal cell wall thickenings were not affected by excess Fe in the root BP. Si application under excess Fe exaggerated the effects of excess Fe on root cell wall thickening, increased POD activity but reduced H2O2 content in the root AP. Thus, Si application under excess Fe nutrition promotes earlier initiation of lignin polymerization closer to and toward the root tip and hence restricts the entry of excess Fe into the plant.

Formation of root silica aggregates in sorghum is an active process of the endodermis.

Silica deposition in plants is a common phenomenon that correlates with plant tolerance to various stresses. Deposition occurs mostly in cell walls, but its mechanism is unclear. Here we show that metabolic processes control the formation of silica aggregates in roots of sorghum (Sorghum bicolor L.), a model plant for silicification. Silica formation was followed in intact roots and root segments of seedlings. Root segments were treated to enhance or suppress cell wall biosynthesis. The composition of endodermal cell walls was analysed by Raman microspectroscopy, scanning electron microscopy and energy-dispersive X-ray analysis. Our results were compared with in vitro reactions simulating lignin and silica polymerization. Silica aggregates formed only in live endodermal cells that were metabolically active. Silicic acid was deposited in vitro as silica onto freshly polymerized coniferyl alcohol, simulating G-lignin, but not onto coniferyl alcohol or ferulic acid monomers. Our results show that root silica aggregates form under tight regulation by endodermal cells, independently of the transpiration stream. We raise the hypothesis that the location and extent of silicification are primed by the chemistry and structure of polymerizing lignin as it cross-links to the wall.

Surveillance of cell wall diffusion barrier integrity modulates water and solute transport in plants

The endodermis is a key cell layer in plant roots that contributes to the controlled uptake of water and mineral nutrients into plants. In order to provide such functionality the endodermal cell wall has specific chemical modifications consisting of lignin bands (Casparian strips) that encircle each cell, and deposition of a waxy-like substance (suberin) between the wall and the plasma membrane. These two extracellular deposits provide control of diffusion enabling the endodermis to direct the movement of water and solutes into and out of the vascular system in roots. Loss of integrity of the Casparian strip-based apoplastic barrier is sensed by the leakage of a small peptide from the stele into the cortex. Here, we report that such sensing of barrier integrity leads to the rebalancing of water and mineral nutrient uptake, compensating for breakage of Casparian strips. This rebalancing involves both a reduction in root hydraulic conductivity driven by deactivation of aquaporins, and downstream limitation of ion leakage through deposition of suberin. These responses in the root are also coupled to a reduction in water demand in the shoot mediated by ABA-dependent stomatal closure.

Root Anatomical Structure of &amp;lt;i&amp;gt;Jatropha curcas&amp;lt;/i&amp;gt; Seedlings—A Short Report

Jatropha curcas has been expected as a biodiesel plant which can be grown in degraded lands. The structure of roots at the seedling stage, in particular cell wall modification in exodermis and endodermis, was microscopically observed. In addition, it was discussed if the first four peripheral roots that emerge from the base of the primary root (taproot) are lateral roots or adventitious roots. The primary root and the first-order lateral roots formed diarchy stele, in which two protoxylem poles present in primary xylem of root. Consequently, the first four peripheral roots cannot be lateral roots, but should be adventitious roots formed at the base of hypocotyl. In both the primary and first-order lateral roots, exodermis and endodermis formed highly lignified cell walls. Moreover, the exodermal and endodermal cell walls formed Casparian strips, which could be observed without special staining by fluorescent dye under ultraviolet microscopy. Such cell-wall modification in root exodermis and endodermis may play an important role for J. curcas under soil stresses in degraded lands.

Magnesium deficiency affects secondary lignification of the vascular system in Citrus sinensis seedlings

Mg deficiency affected only the differentiation zone in Citrus sinensis roots. Phloem impairment in Mg-deficient leaves resulted in cell wall lignifications of both vascular cambium and spongy parenchyma cells. Decrease of Mg content in the roots hampered secondary lignification of endodermal and protoxylem cell walls. Magnesium (Mg) is a vital nutrient for plant photosynthesis and biochemical reactions. Mg deficiency is a widespread problem in citrus production, directly affecting yield and quality. With the objective of investigating the relationship among root and leaf anatomy, photosynthetic efficiency and mineral nutrient uptake and transport in Mg-deficient citrus, the effects of Mg deficiency in ‘Xuegan’ (Citrus sinensis) seedlings on plant biomass, leaf gas exchange and chlorophyll, nutrient contents, root and leaf anatomy and lignin biosynthesis were studied. Mg deficiency decreased root and shoot dry weight, leaf CO2 assimilation, chlorophyll and Mg, phosphorus (P), boron (B), cupper (Cu) and iron (Fe) concentration in roots, stems and leaves, and increased potassium (K) and calcium (Ca) concentration. Mg deficiency in the leaves resulted in phloem disorder that blocked phloem transport, leading to carbohydrate accumulation in chloroplasts and secondary lignifications of both vascular cambium and spongy parenchyma cell walls. In contrast, decrease of Mg content in the roots hampered lignin deposition on the protoxylem and endodermal cell walls at the root differentiation zone. Poorly lignified Casparian strip and xylem cell walls in Mg-deficient root tips might decrease xylem loading efficiency of nutrients, lowering their contents in the above ground parts, which ultimately inhibited whole plant growth.

Spatial Expression and Functional Analysis of Casparian Strip Regulatory Genes in Endodermis Reveals the Conserved Mechanism in Tomato.

Casparian strip (CS) is an impregnation of endodermal cell wall, forming an apoplastic diffusion barrier which forces the symplastic and selective transport of nutrients across endodermis. This extracellular structure can be found in the roots of all higher plants and is thought to provide the protection of vascular tissues. In Arabidopsis, a genetic toolbox regulating the formation of Casparian strips has emerged recently. However, Arabidopsis has the stereotypical root which is much simpler than most other plant species. To understand the Casparian strip formation in a more complex root system, we examined CS regulatory pathways in tomato. Our results reveal a spatiotemporally conserved expression pattern of most essential components of CS machinery in tomato. Further functional analyses verify the role of homologous CS genes in the Casparian strip formation in tomato, indicating the functional conservation of CS regulatory cascade in tomato.

The odd roots of Campylocentrum (Angraeciinae-Orchidaceae): an anatomical study of its morphologically variable roots

Abstract Although some anatomical studies have been performed in Angraecinae, knowledge about the anatomy of the genus Campylocentrum is as yet incipient. The aim of this study is to anatomically characterize the structure of the different kinds of roots in the genus. Roots from 12 species were analyzed, including all the morphological variation in the genus (smooth and granulose surface). The leafless species are characterized by endovelamen, exodermal and endodermal cell walls thicker than in the leafy species. The species with terete leaves can be split in two groups: one constituting C. poeppigii, whose roots have a granulose surface produced by numerous unicellular, absorbent hairs; the second formed by six species from the Atlantic Forest. In this second group, the same granulose root appearance is produced by tufts of epivelamen in addition to the unicellular, absorbent root hairs. The other species in the genus, with conduplicate leaves, do not present a pattern for grouping. Some of them, such as C. serranum and C. micranthum, share a similar structure with the leafless species, but with thinner exodermal and endodermal cell walls. Other species, such as C. crassirhizum and C. jamaicense, are the only ones in the genus with ○-thickened cells in the exodermis.