As master transcription factors of stomatal development, SPEECHLESS, MUTE, and FAMA, collectively termed SMFs, are primary targets of molecular genetic analyses in the model plant Arabidopsis thaliana. Studies in other model systems identified SMF orthologs as key players in evolutionary developmental biology studies on stomata. However, recent studies on the astomatous liverwort Marchantia polymorpha revealed that the functions of these genes are not limited to the stomatal development, but extend to other types of tissues, namely sporophytic setal and gametophytic epidermal tissues. These studies provide insightful examples of gene-regulatory network co-opting, and highlight SMFs and related transcription factors as general toolkits for novel trait evolution in land plant lineages. Here, we critically review recent literature on the SMF-like gene in M. polymorpha and discuss their implications for plant evolutionary biology.

Smooth scouringrush is a creeping perennial with a high silica content in stems that may impede herbicide uptake. Smooth scouringrush has become a troublesome weed in no-till cropping systems across eastern Washington. In previous field studies, glyphosate provided inconsistent control of smooth scouringrush. The objective of this study was to determine if the addition of an organosilicone surfactant to glyphosate would improve the efficacy and consistency of control through stomatal flooding. To test this hypothesis, glyphosate was applied at three field sites at 3.78 kg ae ha–1 alone, with an organosilicone surfactant (OS1 or OS2), an organosilicone plus nonionic surfactant blend, or an alcohol-based surfactant applied during the day or at night. Stem counts were recorded 1 yr after herbicide applications. Five of the six effective treatments observed across the three study sites included organosilicone surfactant or an organosilicone plus nonionic surfactant blend. At two sites, when there was a difference in efficacy between application times; daytime applications were more effective than nighttime applications. These results support the hypothesis of stomatal flooding as a likely mechanism for enhanced efficacy of glyphosate with the addition of an organosilicone surfactant. However, at one site, the treatments containing organosilicone surfactant were more efficacious when applied at night than during the day. At this site, high daytime temperatures and low relative humidity may have resulted in rapid evaporation of spray droplets. The addition of an organosilicone surfactant to glyphosate is recommended for smooth scouringrush control, and daytime treatments are preferred but should be applied when temperatures and humidity are not conducive to rapid droplet drying. Further research is necessary to confirm that stomatal flooding is responsible for improved glyphosate efficacy.

As the interface between plants and the environment, the leaf epidermis provides the first layer of protection against drought, ultraviolet light, and pathogen attack. This cell layer comprises highly coordinated and specialised cells such as stomata, pavement cells and trichomes. While much has been learned from the genetic dissection of stomatal, trichome and pavement cell formation, emerging methods in quantitative measurements that monitor cellular or tissue dynamics will allow us to further investigate cell state transitions and fate determination in leaf epidermal development. In this review, we introduce the formation of epidermal cell types in Arabidopsis and provide examples of quantitative tools to describe phenotypes in leaf research. We further focus on cellular factors involved in triggering cell fates and their quantitative measurements in mechanistic studies and biological patterning. A comprehensive understanding of how a functional leaf epidermis develops will advance the breeding of crops with improved stress tolerance.

Cotton fibre yield and quality are markedly influenced by drought and high-temperature stress. We examined the traits of the leaf stomata in 39 cotton genotypes subjected to exogenous phytohormone abscisic acid (ABA) signalling, electrolyte leakage under 40°C thermal stress, and relative GhHsfA, GhbZIP and GhHSP70 expression levels under two treatments. Stomatal density and area ranged from 66 to 182/mm2 and 663 to 1305 μm2, respectively. Under exogenous ABA signalling, the changes in stomatal aperture (ΔSAp) were in the range of 2.5–31.2%; ΔSAp and relative GhHsfA, GhbZIP and GhHSP70 expression levels were significantly correlated, respectively. Electrolyte leakage increased unequally among cotton genotypes after heat stress. The changes in electrolyte leakage (ΔEL) and relative GhHsfA, GhbZIP and GhHSP70 expression levels were very strongly correlated, respectively. Their relative expression levels could be used as references for the rapid identification of stress-tolerant cotton strains. Cluster analysis of the 39 cotton genotypes indicated that Xinluzao36, Shiyang1, shinong98-7 and Zhongmiansuo293 are heat- and drought-resistant. We integrated both analysis of physiological parameters and molecular methods to identify cotton varieties with the drought and heat tolerance, in order to provide a reference for the selection of materials and methods for the research and production of cotton.

Individual plant stomata were studied within a sealed environmental chamber that encloses a volume of space around a microscope objective. A leaf that is attached to a plant is secured to a temperature-controlled microscope stage, and the top surface of the leaf is illuminated via the microscope's light source while stomata on the underside of the leaf are observed through a microscope objective. Stomatal responses are observed on a leaf exposed to environmental conditions including various illuminations and changes in ambient CO2 level, at a given temperature.

Stomata (singular, “stoma”) are tiny pores through which plants breathe. Stomata are found on the upper and lower sides of leaves, on flower petals, on stems, and on roots. Scientists survey plant surfaces to determine the density and size of stomata and relate these findings to properties of the environment, such as temperature and the amounts of sunlight, humidity, oxygen, and carbon dioxide in the air when a leaf is formed. Stomata of various plants are suitable subjects for classroom laboratory activities since they may be examined by light microscopy.

Among grain legumes, faba bean is reputed to be relatively sensitive to drought stress. Epicuticular wax (ECW) quantity is considered as an important drought adaptation strategy in plant species. This study aimed to define variation in leaf ECW concentration as a drought-adaptive trait in 197 faba bean accessions under well-watered conditions. The relationship between ECW and stomatal characteristics was also investigated. Highly significant differences were found in the ECW concentration, which ranged from 0.680 to 2.104 mg/dm2. No relationships were found between ECW and any measure of stomatal morphology and function. This study provides evidence of the wide variation in ECW in faba bean germplasm, which is independent of stomatal characteristics and leaf water content. This variation may allow the genetic improvement of ECW as a drought-adaptive character in faba bean breeding programs aiming at the economical use of water.

Leaf cuticle micromorphology has been cited as an important set of taxonomic characters in gymnosperms, but previous studies have largely been based on small sample sizes. The premise of this study was to understand whether external factors affect cuticular micromorphology of Podocarpaceae. Two example species, Prumnopitys andina and Podocarpus salignus, were studied. Of 21 sampled characters, nine (c.43% of the total) were visually assessed as being moderately reliable or highly reliable for taxonomic discrimination for both species, with an additional six (c.29%) being moderately reliable or highly reliable for only one or other of the example species, and six characters (c.29%) unreliable for both. Seven of the most variable stomatal characters were selected for further analysis to establish whether environmental factors affect them. The relationship between these seven stomatal characters, the environment and climate was analysed using the R ‘vegan’ package and climate data gathered from WorldClim. Our results showed that both species had larger stomata in moist and shady conditions, and a higher density of (smaller) stomata in sunny and drier conditions. An additional novel finding was the presence of stomata on the adaxial leaf surface in 46% of samples of Prumnopitys andina: the first record of adaxial stomata in this species, highlighting the necessity of studying multiple samples of a given species. In conclusion, these results indicate that larger sample sizes than have hitherto been employed in cuticle micromorphological studies are necessary to fully document the amount of phenotypic variation that exists.

Cryofracture of living material and fracture at room temperature of herbarium material were used to obtain cross-sections of the stomatal complexes of four species of Podocarpus (Podocarpaceae) for scanning electron microscopy. Cross-sections of the stomata of one species in Podocarpus subgenus Foliolatus section Foliolatus (Podocarpus rubens), one in Podocarpus section Globulus (Podocarpus beecherae), one in Podocarpus subgenus Foliolatus section Longifoliolatus (Podocarpus insularis) and one in subgenus Podocarpus section Australis (Podocarpus nivalis) were studied. The architecture of the stomatal complex, including the wax plug, is described. It was found that the wax plug sits high in the stomatal antechamber in Podocarpus rubens, P. beecherae and Podocarpus decipiens and about halfway up the chamber in P. nivalis. A ridge, which appears to correspond to the crease where the guard cells meet, exists on the underside of the wax plug in Podocarpus beecherae, P. decipiens and P. rubens; its presence in P. nivalis requires confirmation. In addition, ridges within the stomatal antechamber were observed when viewing the cross-sections of Podocarpus decipiens and P. rubens, the internal surface of the cuticle of P. decipiens, Podocarpus teysmannii, P. insularis and Podocarpus milanjianus, and the external surface of the cuticle of Podocarpus chinensis, Podocarpus macrophyllus and Podocarpus pilgeri. These ridges may consist of wax and be a result of epitaxis.

Growth, development, and germination among jointed goatgrass (Aegilops cylindrica Host. # AEGCY) accessions collected from nine western states were not consistently different in field plots near Pullman, WA, or in the greenhouse. Germination percentage and rate of spikelet germination of all accessions produced in the field and greenhouse were consistently high, averaging about 64% and 5.2 (on a unitless scale of 0 to 7), respectively. The Montana accession germinated consistently less than the others. In a separate greenhouse study comparing only the accessions from Colorado and Nebraska, the accession from Colorado averaged 18, 16, and 15% greater net photosynthesis rate (Pn), transpiration rate (E), and stomatal density, respectively, and 21% lower diffusive resistance (rl) than did the accession from Nebraska. However, growth parameters of the Nebraska accession averaged 7 to 35% greater than for the Colorado accession. Overall, the germination, growth, CO2 fixation, and water use among accessions appeared to be similar when jointed goatgrass was grown under Pacific Northwest conditions.

Fourteen tomato genotypes, eastern black nightshade, and 35 Lycopersicon accessions were screened for tolerance to acifluorfen. Tolerant and susceptible genotypes occurred in most species. Fifteen genotypes were chosen for further study depending on their fresh weight after acifluorfen treatment Over all 15 genotypes, there was no correlation between trichome density and acifluorfen tolerance; however, in L. esculentum, cultivars with the most trichomes were the most tolerant There was an inverse relationship between stomata density and tolerance. Amount and composition of epicuticular wax and cuticle thickness did not correlate to acifluorfen tolerance.

Adaxial and abaxial epidermal surfaces of johnsongrass leaves were studied to determine which cells contribute to leaf microroughness. Cork-silica cell (CSC) pairs, three types of prickles, macrohairs, bicellular trichomes, stomata, and ordinary short and long epidermal cells were found and described. CSC pairs made up about 22% of all cells and probably contribute more to microroughness than any other single type because each cork cell produces 11 ± 3 wax filaments that are up to 100 μm long. Bicellular trichomes represented 4 to 5% of the total cells but decreased leaf roughness by secreting a type of mucilage that covers microscopic wax crystals. Stomatal complexes comprised 15 to 18% of all cells and contributed to leaf roughness because they are slightly recessed below the leaf surface. Long prickles occur primarily over veins and represent less than 1% of all cells. Small prickles were present primarily on adaxial surfaces and represent only 3% of all cells. Macrohairs were the largest appendages, 237 ± 104 μm, but they represent far less than 1% of all cells and occur primarily over veins. Ordinary short cells comprised 6 to 13% of all cells. Long cells were most common (41%) of all cells. Short and long cells contribute to leaf roughness because the surface is often convex. A typical johnsongrass leaf may contain more than 25 million appendages on each surface that increase the roughness already caused by epicuticular wax crystals.

Net (apparent) photosynthesis rate (Pn) of jointed goatgrass (Aegilops cylindrica Host # AEGCY) leaves in the greenhouse became light saturated at a photosynthetic photon flux density (PPFD) of about 1000 μE·m–1-2·s–1 with a maximum Pn of 27 mg CO2 ·dm–2 ·h–1. Diffusive resistance to water vapor (rl) of adaxial leaf surfaces was 43% that of abaxial surfaces, in part, because stomatal density was 50% greater on adaxial leaf surfaces than on abaxial surfaces. Dark respiration rate (Rd) was 1.6 mg CO2 ·dm−2·h−1. Light compensation point (CPl) was 21 μE·m−2·s−1 and CO2 compensation point (CPc) was 32 ppmv. In the field, where light intensity and temperature were greater than in the greenhouse, leaves became light saturated for Pn at a higher intensity, and Rd and CPl were three times greater than in the greenhouse. Pn and Rd of spikes at anthesis were at least 30% less and 200% greater, respectively, than the values for leaves.

Absorption of triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} by tanoak [Lithocarpus densiflorus (Hook. & Am.) Rehd.] leaves was investigated. Greater amounts of 14C-triclopyr were absorbed by immature leaves than mature leaves and by abaxial than adaxial surfaces. Both surfaces of immature and mature tanoak leaves were characterized. Stomata were present only on the abaxial surface and were more numerous on immature leaves than mature leaves. Immature leaves had less epicuticular wax and thinner, more permeable cuticular membranes than mature leaves. Stellate trichome densities were greater on abaxial surfaces than adaxial surfaces and on immature than mature leaves. Absorption of 14C-triclopyr was influenced by each of the leaf surface features studied.

Araucaria goroensis R.R.Mill & Ruhsam sp. nov., a new monkey puzzle species from New Caledonia, is described and illustrated with photographs from the field and from herbarium specimens. Previously confused with Araucaria muelleri, it is more similar to A. rulei. It is distinguished from the latter species by its larger leaves, microsporophylls without a shouldered base, and shorter female cone bracts. It occurs in a very limited area of south-east New Caledonia, where its existence is threatened by nickel mining. Using the guidelines of the International Union for Conservation of Nature, we propose an assessment of Endangered for the new species and reassess Araucaria muelleri also as Endangered. A key to the seven species in the ‘large-leaved clade’ of New Caledonian species of Araucaria is given. The name Eutassa latifolia de Laub. is synonymised with Araucaria muelleri, and the recent typification of the latter name by Vieillard 1276 is rejected. Detailed reasoning is given for these nomenclatural acts.

To investigate the Holocene climate and treeline dynamics in the European Russian Arctic, we analysed sediment pollen, conifer stomata, and plant macrofossils from Lake Kharinei, a tundra lake near the treeline in the Pechora area. We present quantitative summer temperature reconstructions from Lake Kharinei and Lake Tumbulovaty, a previously studied lake in the same region, using a pollen–climate transfer function based on a new calibration set from northern European Russia. Our records suggest that the early-Holocene summer temperatures from 11,500 cal yr BP onwards were already slightly higher than at present, followed by a stable Holocene Thermal Maximum (HTM) at 8000–3500 cal yr BP when summer temperatures in the tundra were ca. 3°C above present-day values. A Picea forest surrounded Lake Kharinei during the HTM, reaching 150 km north of the present taiga limit. The HTM ended with a temperature drop at 3500–2500 cal yr BP associated with permafrost initiation in the region. Mixed spruce forest began to disappear around Lake Kharinei at ca. 3500 cal yr BP, with the last tree macrofossils recorded at ca. 2500 cal yr BP, suggesting that the present wide tundra zone in the Pechora region formed during the last ca. 3500 yr.

Two species of invasive goldenrods, Solidago canadensis and Solidago gigantea, are spread over all territories of Lithuania. Solidago × niederederi, a putative hybrid between S. canadensis and native Solidago virgaurea, was found in 27 populations mixed with the parental species. This research represents the characterization of S. × niederederi in comparison to the other mentioned Solidago species, with the use of one-way analysis of variance (ANOVA), principal-components analysis (PCA), and discriminant analysis of a large data set. Twenty quantitative, four qualitative, and five ratio morphological and anatomical characteristics, pollen viability, and somatic chromosome numbers of the four Solidago species were studied with the aim to ascertain inter- and intraspecific variation and reliable features identifying S. × niederederi, and to test the hypothesized hybrid origin. The PCA of morphological and anatomical characteristics showed the clear intermediate position of S. × niederederi compared to S. canadensis and S. virgaurea. The results showed that the most informative characteristics for the distinction of hybrids from parental species are floral traits such as the lengths of the disc, ray florets, and involucre. The intermediate stomatal characteristics and sharply decreased pollen viability discovered herein could potentially be used as an additional discriminating character in Solidago hybrid identification and support the hybrid origin of S. × niederederi.

Swartzia langsdorffii seeds have recalcitrant characteristics. Nonetheless, dispersal begins in the month with the lowest precipitation in the studied region, which could lead to seed death by desiccation. Therefore, the objectives of this study were: (1) to characterize the physiological behaviour of S. langsdorffii seeds related to their desiccation sensitivity/tolerance; and (2) to assess the morphophysiological characteristics that enable the seeds to remain viable after dispersal. Fruits and seeds were subjected to biometric evaluation and the anatomical and ultrastructural features of the seeds were determined. Field assessments were performed to determine the capacity of the seeds to maintain viability and to verify the relation between seed viability, diaspore water content and environmental variables. Seeds of this species were found to be recalcitrant and showed pores distributed throughout the seed coat, and contained a large number of stomata in the hypocotyl–radicle axis epidermis. Moreover, phenolic compounds were found throughout the radicle region. Seeds remained viable in the soil for up to 7 months after dispersal without a significant decrease in water content, despite the low precipitation and soil water content. Radicle protrusion began 5 months after dispersal and coincided with partial fruit decomposition at the beginning of the rainy season. Thus, the possible microclimate created by the pericarp, with the moisture content of the aril and the soil, the presence of the structures in the axis, such as the pores and stomata, the chemical composition and the morphology of S. langsdorffii seeds could favour maintenance of their viability until the beginning of the rainy season.