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The upside-down water collection system of Syntrichia caninervis
Abstract
Desert plants possess highly evolved water conservation and transport systems, from the root structures that maximize absorption of scarce ground water1, 2, 3, 4, 5, to the minimization of leaf surface area6 to enhance water retention. Recent attention has focused on leaf structures that are adapted to collect water and promote nucleation from humid air7, 8, 9. Syntrichia caninervis Mitt. (Pottiaceae) is one of the most abundant desert mosses in the world and thrives in an extreme environment with multiple but limited water resources (such as dew, fog, snow and rain), yet the mechanisms for water collection and transport have never been completely revealed. S. caninervis has a unique adaptation: it uses a tiny hair (awn) on the end of each leaf to collect water, in addition to that collected by the leaves themselves. Here we show that the unique multiscale structures of the hair are equipped to collect and transport water in four modes: nucleation of water droplets and films on the leaf hair from humid atmospheres; collection of fog droplets on leaf hairs; collection of splash water from raindrops; and transportation of the acquired water to the leaf itself. Fluid nucleation is accomplished in nanostructures, whereas fog droplets are gathered in areas where a high density of small barbs are present and then quickly transported to the leaf at the base of the hair. Our observations reveal nature's optimization of water collection by coupling relevant multiscale physical plant structures with multiscale sources of water.
... The microscopic observations of the hairpoint suggested that they can be smooth or spinulose. The hairpoint captures small drops of water from the atmosphere (Supporting Video 4) as first pointed out by Pan et al., (2016). The grooves from the projections in a spinulose hairpoint are able to form nano drops of free water. ...
... The grooves from the projections in a spinulose hairpoint are able to form nano drops of free water. As the drops of water expand, they can be conducted towards the lamina and become available to the moss (Pan et al., 2016). Moreover, Tao and Zhang (2012), showed that the presence of the hairpoint influenced water relations in the moss Syntrichia by increasing water content and delaying evaporation rates. ...
... The hairpoint might function in several ways. Pan et al., (2016) demonstrated that hairpoint is able to capture small nanodrops of water from the atmosphere and conduct them toward the lamina in S. caninervis and suggested this may be an adaptation in mosses living in xerophytic environments. In addition, the hairpoint may function to minimize water loss by reflecting the sunlight and creating a boundary layer (Scott, 1982;Tao and Zhang, 2012). ...
Syntrichia relies on external water conduction for photosynthesis, survival, and reproduction, a condition referred to as ectohydry. Capillarity spaces are abundant in Syntrichia, but the link between function and morphology is complex. The aim of this study was to provide a better understanding of species-specific morphological traits underlying functions of water conduction and storage. We used an environmental scanning electron microscope (ESEM) and confocal microscopy for observing anatomical characters in the leaves of Syntrichia species. We also measured hydration/dehydration curves to understand the rate of conduction and dehydration by experimental approaches. Syntrichia is an ectohydric moss that can externally transport and store water from the base of the stem using capillary action. We propose a new framework to study ectohydric capabilities, which incorporates three morphological scales and the timing of going from completely dehydrated to fully hydrated. Characters of interest in this model include: cell anatomy (papillae development, hyaline basal cells, and laminar cells), architecture of the stem (concavity and orientation), and whole clump characteristics (density of stems). We report significant variation in the speed of conduction, water holding capacity, and hydration associated with each species studied (11 in total). All Syntrichia species are capable of external water conduction and storage, but the relevant traits differ among species. These results help to understand potential evolutionary and ecological tradeoffs among speed of water conduction, water holding capacity, ontogeny, and differing habitat requirements. An integrative view of ectohydry in Syntrichia contributes to understanding the water relationships of mosses.
... This moss has developed a remarkable function to collect water effi-ciently, which is enabled by its hierarchical structure ( Figure 1C, dry and rehydrated state). 40 Scanning electron microscopy (SEM) revealed both grooves and small barbs on its tiny hair (awn). The initial nucleation appears in nanogrooves located within a microgroove or a shallow cavity, and further growth takes place in regions with a high barb density. ...
... 23 (C) The water droplet nucleates, grows, transports from the hair to the leaf, and is absorbed by the mosses. 40 (D) The fog capture process on the gradient conical-shaped setae of desert scorpion. 41 (E) The shorebird is capable of capturing water through its beak of concave curvature gradient structure by opening and closing the beak repeatedly. ...
Many biological surfaces are capable of transporting liquids in a directional manner without energy consumption. Inspired by nature, constructing asymmetric gradient surfaces to achieve desired droplet transport, such as a liquid diode, brings an incredibly valuable and promising area of research with a wide range of applications. Enabled by advances in nanotechnology and manufacturing techniques, biomimetics has emerged as a promising avenue for engineering various types of anisotropic material system. Over the past few decades, this approach has yielded significant progress in both fundamental understanding and practical applications. Theoretical studies revealed that the heterogeneous composition and topography mainly govern the wetting mechanisms and dynamics behavior of droplets, including the interdisciplinary aspects of materials, chemistry, and physics. In this review, we provide a concise overview of various biological surfaces that exhibit anisotropic droplet transport. We discussed the theoretical foundations and mechanisms of droplet motion on designed surfaces and reviewed recent research advances in droplet directional transport on designed plane surfaces and Janus membranes. Such liquid-diode materials yield diverse promising applications, involving droplet collection, liquid separation and delivery, functional textiles, and biomedical applications. We also discuss the recent challenges and ongoing approaches to enhance the functionality and application performance of anisotropic materials.
... Its leaves feature long white "awns" at their tips, which efficiently collect and transport water from the air, while also reflecting sunlight to minimize water evaporation. This adaptation allows S. caninervis to flourish in arid environments [9]. In semi-humid regions, the large palmate leaves of Populus tomentosa possess a non-wettability hollow white tomentose layer on their back surfaces, which reflects up to 55% of sunlight. ...
... However, the watercollection efficiency of trichomes, either a single trichome or multiple trichomes, has not been thoroughly investigated in this study, which needs to be further examined in the fu-ture. Compared with other water-collection systems, such as 1D fibers [8,9], highly irregular 2D surfaces [55], and 3D leaf-trichome hierarchical structures [27], each umbrella-shaped ratchet trichome on the E. angustifolia leaf surface is an independent microsystem with a 3D interface structure composed of 1D and 2D structures that can collect water hierarchically (Figure 8), enabling the capture of water droplets and the directional transport of water. In the natural environment, the apex of the trichomes on the abaxial surface of E. angustifolia leaves is facing the ground, like many umbrella-shaped containers hanging upside down. ...
Leaves are essential for plants, enabling photosynthesis and transpiration. In arid regions, water availability limits plant growth. Some plants, like Elaeagnus angustifolia, a sandy sub-tree species widely distributed in arid and semi-arid regions, have unique leaf structures to reduce water loss and solar radiation. Here, we describe the leaves of Elaeagnus angustifolia L., with special functioning trichomes. Through leaf submicroscopic structure observation, in situ water collection experiments, photosynthesis measurements, and reflection spectrum analysis, we investigated E. angustifolia leaves, focusing on their functioning trichomes. These trichomes capture water vapor, reflect UV and NIR light, and possess a 3D interface structure composed of 1D and 2D structures. The 1D conical structure captures water droplets, which are then gathered by the radial conical structure and guided towards the stomata through wedge-shaped grooves on the 2D umbrella structure. The trichomes also reflect sunlight, with micropapillae reflecting UV light and the umbrella structure reflecting NIR light. These mechanisms reduce leaf temperature, respiration, and water transpiration, protecting against solar radiation damage. This study provides insights into water collection and light-reflection mechanisms, revealing adaptive strategies of plants with large leaves in arid regions.
... The interactions between liquid drops and fibres is ubiquitous in a wide range of situations including liquid aerosol filtering (Agranovski & Braddock 1998;Zhang et al. 2015), coating processes (Quéré 1999;Chan et al. 2021), digital microfluidics (Gilet, Terwagne & Vandewalle 2009 and fog harvesting (Klemm 2012;Labbé & Duprat 2019). The latter has also motivated research of droplets interacting with biological systems (Malik et al. 2014) such as threads of spider silk (Zheng et al. 2010;Ju, Zheng & Jiang 2014) and plants with fibre-like features such as sequoia needles, cactus spines, grass blades and moss leaves (Limm et al. 2009;Ju et al. 2012;Roth-Nebelsick et al. 2012;Pan et al. 2016) that are able to efficiently capture and transport water droplets. In most of these examples, the fibre is generally not still but subject to motion due to external forcing such as wind. ...
... Bostwick & Steen (2014) rationalized their existence by adapting the Rayleigh-Lamb theory of vibrating free drops (Rayleigh 1879;Lamb 1924) to sessile drops. The combination of both rocking and pumping responses, and in particular their phase difference (Noblin, Kofman & Celestini 2009), can trigger directional motion. On slanted substrates, a pumping mode alone can trigger motion if the periodic evolution of the wetted area unpins the droplet. ...
We study experimentally the dynamics of a water droplet on a tilted and vertically oscillating rigid fibre. As we vary the frequency and amplitude of the oscillations the droplet transitions between different modes: harmonic pumping, subharmonic pumping, a combination of rocking and pumping modes, and a combination of pumping and swinging modes. We characterize these responses and report how they affect the sliding speed of the droplet along the fibre. The swinging mode is explained by a minimal model making an analogy between the droplet and a forced elastic pendulum.
... In arid or semiarid regions, the evolution of diverse flora and fauna has resulted in various survival strategies to access water despite the challenging conditions. Many of these living organisms utilize naturally occurring atmospheric water, either through fog collection [1][2][3][4] or promoting condensation [5]. Once collected, water must be transported to the area where the organism can absorb it. ...
From microfluidics to fog-harvesting applications, tiny droplets are transported along various solid substrates including hairs, threads, grooves, and other light structures. Driven by gravity, a droplet sliding along a vertical fiber is a complex problem since it is losing volume and speed as it goes down. With the help of an original setup, we solve this problem by tracking in real-time droplet characteristics and dynamics. Single fibers as well as multiple fiber systems are studied to consider the presence of grooves. On both fibers and grooved threads, droplet speed and volume are seen to decay rapidly because the liquid entity is leaving a thin film behind. This film exerts a capillary force able to stop the droplet motion before it is completely drained. A model is proposed to capture the droplet dynamics. We evidence also that multiple vertical fibers are enhancing the droplet speed while simultaneously promoting increased liquid loss on grooves.
... The porous structure at this scale denotes largerscale fiber assemblies. Larger scale structures, such as the fiber network, transport water by wicking in the inter-fiber pores spaces, as also occurs in desert plants 47 . Single fibers consist of a bundle of cells. ...
Emerging atmospheric water harvesting (AWH) technologies hold promise for water supply to underdeveloped regions with limited access to liquid water resources. The prevailing AWH systems, including condensation- or sorption-based, mostly rely on a single mechanism limited by working conditions and inferior performance. Here, we synergistically integrate multiple mechanisms, including thermosorption effect, radiative cooling, and multiscale cellulose-water interactions to improve the water harvesting performance with minimal active energy input over a relative humidity (RH) range between 8% to 100%. The proposed system consists of a scalable and sustainable cellulose scaffold impregnated with hygroscopic lithium chloride (LiCl). Cellulose scaffold and LiCl synergistically interact with water at molecular, nanometer, and micrometer scales, achieving a high yield (2.5–16 kg kg ⁻¹ at 60–90% RH). The captured water in return facilitates radiative cooling due to its intrinsically high infrared emissivity. An outdoor batch-mode AWH device shows a water uptake up to 6.75 L kg ⁻¹ day ⁻¹ with a material cost as low as 3.15–5.86 USD kg ⁻¹ . A theoretical model is also proposed to elucidate the synergistic AWH mechanisms among cellulose-LiCl-water-energy interaction. This AWH strategy provides a potential solution to water scarcity problems in regions with larger seasonal and climate variations, especially arid areas.
... This enhancement is attributed to an asymmetry in the energy barrier for droplet spreading in modes parallel and perpendicular to the microgrooves. [113][114][115] Moreover, the microgrooves may induce capillary imbibition, further enhancing the transport. [116][117][118][119] Combining nanostructure-induced superhydrophilicity 34 with microgrooves, 101 we would expect an even shorter onset time (i.e., faster liquid transport), and may warrant a systematic study in the future. ...
Collecting microscale water droplets suspended in the wind, that is, fog, using permeable surfaces is a promising solution to the worldwide problem of water scarcity and is of great interest to industries, such as mist elimination and recapturing water in cooling towers. In the past few decades, this topic has attracted a drastically increasing number of researchers across a wide range of subjects. However, many aspects remain unclear, such as the definition and process of fog collection, fog collection determined from the perspectives of both the fog capture process and the liquid transport process, and how surface characteristics affect fog collection performance. In this review, we introduce and discuss fog collection from the perspectives of aerodynamics‐governed fog‐capturing processes and interfacial‐phenomena‐determined liquid transport processes. Then, an emphasis is given to the design and engineering of permeable surfaces at different length scales to optimize the fog collection performance, including the dimension, morphology, and arrangement of wires at the millimetric scale, unidirectional spreading, and Laplace pressure gradient induced by asymmetric surface geometry and nano‐/microstructures. At last, a brief outlook of future research directions is provided.
Plants and animals that thrive in arid regions utilize the diurnal changes in environmental temperature and humidity to optimize their water budget by combining water-harvesting mechanisms and morphophysiological traits. The Athel tamarisk ( Tamarix aphylla ) is a halophytic desert shrub that survives in arid, hypersaline conditions by excreting concentrated solutions of ions as droplets on its surface that crystallize into salt crystals and fall off the branches. Here, we describe the crystallization on the surface of the plant and explore the effects of external conditions such as diurnal changes in humidity and temperature. The salt mixtures contain at least ten common minerals, with NaCl and CaSO 4 ·2H 2 O being the major products, SiO 2 and CaCO 3 main sand contaminants, and Li 2 SO 4 , CaSO 4 , KCl, K 2 Ca(SO 4 ) 2 ·H 2 O, CaMg(CO 3 ) 2 and AlNaSi 3 O 8 present in smaller amounts. In natural conditions, the hanging or sitting droplets remain firmly attached to the surface, with an average adhesion force of 275 ± 3.5 µN measured for pure water. Rather than using morphological features of the surface, the droplets adhere by chemical interactions, predominantly by hydrogen bonding. Increasing ion concentration slightly increases the contact angle on the hydrophobic cuticle, thereby lowering surface wettability. Small amounts of lithium sulfate and possibly other hygroscopic salts result in strong hygroscopicity and propensity for deliquescence of the salt mixture overnight. Within a broader context, this natural mechanism for humidity harvesting that uses environmentally benign salts as moisture adsorbents could provide a bioinspired approach that complements the currently available water collection or cloud-seeding technologies.
Although the desert moss Syntrichia caninervis Mitt. is extremely desiccation tolerant, it still requires water and photosynthates for growth. The ecological significance of the leaf angle in maintaining a balance between water and light availability is critical to its survival. Active leaf repositioning balances water and light availability following rehydration. S. caninervis can adjust leaf angles from a steep (84-69 degrees) to a stable level at 30 degrees within 7 s after rehydration, obtaining maximum net photosynthetic gain at a shoot relative water content of similar to 60%. Leaf morphological characters, (leaf hair points, surface papillae and costal anatomy) and ultrastructural changes (chloroplast reordering and loss of lipid reserves as shown by changes in osmiophilic globules) were linked to rapid leaf spreading, water gain and sunlight reflectivity of leaves during rehydration. The high 377.20 +/- 91.69 (cm(2) g(-1)) surface area to mass ratio was a major factor in facilitating the rapid response to rewetting. Hyaline cells of the leaf base absorbed water, swelled and forced the leaf away from the stem as soon as rehydration commenced. Loss of leaf hair points retards leaf angle adjustment during rehydration.
Fog represents a large, untapped source of potable water, especially in arid climates. Numerous plants and animals use textural as well as chemical features on their surfaces to harvest this precious resource. In this work, we investigate the influence of surface wettability characteristics, length scale, and weave density on the fog harvesting capability of woven meshes. We develop a combined hydrodynamic and surface wettability model to predict the overall fog collection efficiency of the meshes and cast the findings in the form of a design chart. Two limiting surface wettability constraints govern re-entrainment of collected droplets and clogging of mesh openings. Appropriate tuning of the wetting characteristics of the surfaces, reducing the wire radii, and optimizing the wire spacing all lead to more efficient fog collection. We use a family of coated meshes with a directed stream of fog droplets to simulate a natural foggy environment and demonstrate a five-fold enhancement in the fog-collecting efficiency of a conventional polyolefin mesh. The design rules developed in this work can be applied to select a mesh surface with optimal topography and wetting characteristics to harvest enhanced water fluxes over a wide range of natural convected fog environments.
Multiple biological structures have demonstrated fog collection abilities, such as beetle backs with bumps and spider silks with periodic spindle-knots and joints. Many Cactaceae species live in arid environments and are extremely drought-tolerant. Here we report that one of the survival systems of the cactus Opuntia microdasys lies in its efficient fog collection system. This unique system is composed of well-distributed clusters of conical spines and trichomes on the cactus stem; each spine contains three integrated parts that have different roles in the fog collection process according to their surface structural features. The gradient of the Laplace pressure, the gradient of the surface-free energy and multi-function integration endow the cactus with an efficient fog collection system. Investigations of the structure-function relationship in this system may help us to design novel materials and devices to collect water from fog with high efficiencies.
The wetting and spreading of liquids on solids is frequently encountered in the chemical industry. This paper presents some simple but powerful thermodynamic concepts that can be taught in a 1-hour lecture on wetting and spreading. We approach the subject through the theme of the minimization of free energy - a concept with which chemical engineering students are well acquanted.
It is postulated that the Australian angiosperm flora ins derived from a sample of a one-time world flora of about 180 families that entered Australia by a land bridge from Asia. Many of the genera that entered still persist. New genera evolved in all habitats, many from lineages which were adapted to soils of low fertility determined primarily by phosphate level. Soil parent materials with the highest phosphate content are derived mainly from the Tertiary basalts in the east and support rainforests (except in cold regions). Soil phosphate levels decrease from east to west across the continent. The number of rainforest genera in any community is usually correlated with soil P. The converse holds for xeromorphic genera. Some rainforest genera therefore are more readily adapted to aridity than to low fertility conditions. Expansion and contraction of the rainforest is determined partly by climate and partly by soil fertility levels. A sudden expansion of the rainforest in the Oligocene occurred when the basalt flows covered part of eastern Australia. Since that time the rainforests have contracted, partly as a result of the removal of basaltic material and partly because of the development of colder climates in the ranges. The absence of rainforest and the paucity of rainforest genera in southwest Western Australia are accounted for by low fertility levels rather than by a decimation of rainforest genera by a past dry climate. Xermorphy, a result of high lignification, heavy cutinization, silicification, or a combination of these may occur in rainforest species. Adaptation to low fertility accentuates xeromorphic characters through a reduction in leaf size. The low fertility xeromorphs are not xerophytes. Anatomical features have little significance in their survival, which is determined by the ability of the plants to withstand long periods of mineral starvation. Experimental work indicates that the degree of xeromorphy can be reduced in many taxa by the addition of phosphorus and nitrate; four different types of leaf response have been identified.
An impact-type Joss-Waldvogel disdrometer (JWD), a two-dimensional video disdrometer (2DVD), and a laser optical OTT Particle Size and Velocity (PARSIVEL) disdrometer (PD) were used to measure the raindrop size distribution (DSD) over a 6-month period in Huntsville, Alabama. Comparisons indicate event rain totals for all three disdrometers that were in reasonable agreement with a reference rain gauge. In a relative sense, hourly composite DSDs revealed that the JWD was more sensitive to small drops (<1 mm), while the PD appeared to severely underestimate small drops less than 0.76 mm in diameter. The JWD and 2DVD measured comparable number concentrations of midsize drops (1-3 mm) and large drops (3-5 mm), while the PD tended to measure relatively higher drop concentrations at sizes larger than 2.44 mm in diameter. This concentration disparity tended to occur when hourly rain rates and drop counts exceeded 2.5 mm h(-1) and 400 min(-1), respectively. Based on interactions with the PD manufacturer, the partially inhomogeneous laser beam is considered the cause of the PD drop count overestimation. PD drop fall speeds followed the expected terminal fall speed relationship quite well, while the 2DVD occasionally measured slower drops for diameters larger than 2.4 mm, coinciding with events where wind speeds were greater than 4 m s(-1). The underestimation of small drops by the PD had a pronounced effect on the intercept and shape of parameters of gamma-fitted DSDs, while the overestimation of midsize and larger drops resulted in higher mean values for PD integral rain parameters.
We use high-speed video imaging to study the capillary-driven motion of a micro-droplet along the outside of a pre-wetted conical fiber. The cones are fabricated on a glass-puller with tip diameters as small as 1 μm, an order of magnitude smaller than in previous studies. The liquid is fed through the hollow fiber accumulating at the fiber tip to form droplets. The droplets are initially attached to the opening as they grow in size before detaching and traveling up the cone. This detachment can produce a transient oscillation of high frequency. The spatial variation of the capillary pressure drives the droplets towards the wider side of the cone. Various liquids were used to change the surface tension by a factor of 3.5 and viscosity by a factor of 1500. Within each droplet size and viscous-dissipation regime, the data for climbing speeds collapse on a single curve. Droplets traveling with and against gravity allow us to pinpoint the absolute strength of the driving capillary pressure and viscous stresses and thereby determine the prefactors in the dimensionless relationships. The motions are consistent with earlier results obtained from much larger cones. Translation velocities up to 270 mm/s were observed and overall the velocities follow capillary-viscous scaling, whereas the speed of the fastest droplets is limited by inertia following their emergence at the cone tip.
Leaf hydrophobicity and water droplet retention are important functional traits among plant species and may be important selective strategies to increase water availability to root systems in arid and semi-arid environments. Hydrophobic canopies may decrease rainfall interception and increase throughfall to the soil. Leaf angle may also influence the ability of water droplets to channel off leaf surfaces. Water droplets may have a greater ability to drain off leaf surfaces with steeper leaf angles which decrease rainfall interception and increase throughfall to the soil. This study examined the relationships between leaf angle, leaf hydrophobicity, and water droplet retention in 11 species from a semi-arid region of Colorado in the western United States. Leaf hydrophobicity of the adaxial and the abaxial leaf surface was measured by calculating the contact angle between a water droplet and the leaf surface. Water droplet retention was measured as the angle at which a water droplet begins to move as a leaf is incrementally tilted from 0° to 90°. Leaf hydrophobicity was greater than leaf angle for 9 species and similar for 2 species. Leaf angle was greater than water droplet retention on the adaxial leaf surface for 8 species and similar for 3 species. Leaf angle was greater than water droplet retention on the abaxial leaf surface for 7 species and similar for 2 species. The relationship between leaf angle and leaf hydrophobicity and the relationship between leaf angle and water droplet retention were weak; however, the relationship between leaf hydrophobicity and water droplet retention was stronger. Results indicate that intercepted water droplets during a rainfall event will likely drain off the leaf surfaces from a majority of the species examined and contribute to throughfall because leaf angle is greater than water droplet retention in these species. The relationship between leaf angle and canopy hydrophobicity may be a significant influence on hydrological processes in arid and semi-arid regions.
The region at Albuquerque differs from that of Tucson in having about two-thirds as much rainfall and much lower winter temperatures. The soil of the mesa is fluviatile in origin and very diverse in composition. The hardpan layer prominent at Tucson is not well developed. The winter annuals and the larger shrubs and cacti are absent. Most of the plants are perennial herbs. The root systems generally penetrate rather deeply, but often have prominent laterals near the surface of the soil. The cacti and a few of the shrubs have a very superficial root system. The larger cacti show a differentiation into anchorage and absorptive roots. The plants of arroyo sides have prominent tap roots varying in length with the height of the plant above the bottom of the arroyo. Storage roots are uncommon and are more characteristic of the moister situations. Vegetative reproduction from roots is common in the plants of unstable soil. While the causes of root variation can be accurately determined only under laboratory conditions, two factors exert a very evident influence, variation in the penetrability of the soil and in its moisture content. The roots of the plants of an association are grouped into rather definite layers, so that root competition is lessened. The composition of an association is probably determined largely by root competition.
The biological soil crusts (BSCs) in the Gurbantunggut Desert, the largest fixed and semi-fixed desert in China, feature moss-dominated BSCs, which play an indispensable role in sand fixation. Syntrichia caninervis Mitt. (S. caninervis) serves as one of the most common species in BSCs in the desert. In this study we examined the morphological structure of S. caninervis from leafy gametophyte to protonema using light and scanning electron microscopy (SEM). We also examined the relationships between the morphological structure of S. caninervis and environmental factors. We found that: (1) this moss species is commonly tufted on the sand surface, and its leaves are folded upwards and twisted around the stem under dry conditions; (2) the cells on both upper and lower leaf surfaces have C-shaped dark papillae, which may reflect sunlight to reduce the damage from high temperature; (3) the leaf costa is excurrent, forming an awn with forked teeth; and (4) the protonema cells are small and thickset with thick cell walls and the cytoplasm is highly concentrated with a small vacuole. In addition, we also found that the protonema cells always form pouches on the tip of the mother cells during the process of cell polarization. Our results suggest that S. caninervis has, through its life cycle, several morphological and structural characteristics to adapt to dry environmental conditions. These morphological features of S. caninervis may also be found in other deserts in the world due to the world-wide distribution of the species.