The comparative study on leaf anatomy and stomata structures of six genera of Taxaceae s. l. was conducted. Leaf anatomical structures were very comparable to each other in tissue shape and their arrangements. Taxus, Austrotaxus, and Pseudotaxus have no foliar resin canal, whereas Amentotaxus, Cephalotaxus, and Torreya have a single resin canal located below the vascular bundle. Among them, Torreya was unique with thick-walled, almost round sclerenchymatous epidermal cells. In addition, Amentotaxus and Torreya were comprised of some fiber cells around the vascular bundle. Also, Amentotaxus resembled Cephalotaxus harringtonia and its var. nana because they have discontinuous fibrous hypodermis. However, C. fortunei lacked the same kind of cells.
Stomata were arranged in two stomatal bands separated by a mid-vein. The most unique stomatal structure was of Taxus with papillose accessory cells forming stomatal apparatus and of Torreya with deeply seated stomata covered with a special filament structure. Some morphological and molecular studies have already been discussed for the alternative classification of taxad genera into different minor families.
The present study is also similar to these hypotheses because each genus has their own individuality in anatomical structure and stomata morphology.
In conclusion, these differences in leaf and stomata morphology neither strongly support the two tribes in Taxaceae nor fairly recognize the monogeneric family, Cephalotaxaceae. Rather, it might support an alternative classification of taxad genera in different minor families or a single family Taxaceae including Cephalotaxus.
In this study, we would prefer the latter one because there is no clear reason to separate Cephalotaxus from the rest genera of Taxaceae. Therefore, Taxaceae should be redefined with broad circumscriptions including Cephalotaxus.
Characters of stem epidermis, leaf epidermis and stoma could be used as important microcosmic morphological characteristic when inheritance trend is studied in Ephedra breeding and identification.
The stomatic density, stoma major axis and mimor axis, stomatic morphylogy, characters of leaf and stem epidermis of 6 Ephedra plants’ stems were examined by SEM.
The stomatic density and characteristic of leaf epidermis and stem epidermis in six Ephedra species was differenc, there were no obvious morphological differences in stoma shape and size. The guard cells were covered with heavy cuticle and sunken stomata, which were the typical characteristics of xerophytes. The stomas of leaf lower epidermis were oblong or hexagon, but the stomas of steam epidermis were narrowed-oblong or dumbbell-shape, they all belonged to anomalous type.
The stoma type and characters of Ephedra plants is stable and conservative, there was no obvious morphological differences in stoma shape and size between species, so it is difficult to distinguish different species by the variance of stomas, but that can be applyed to distinguish Ephedra from others at plant taxonomy.
Micrographs of the abaxial epidermis of P. lambertii. (A) A view of stomatal distribution in longitudinal rows. Between the rows of stomata there are always sclereids beneath the epidermis, indicating that where there are sclereids there are no stomata (scale bar = 100 µm). (B) A view of the epidermis without sclereids (scale bar = 100 µm). (C) A detail of paratetracytic stomata with four subsidiary cells (scale bar = 50 µm).
Plasticity of stomatal distribution pattern and stem tracheid dimensions in Podocarpus lambertii: an ecological study
Leaf and wood plasticity are key elements in the survival of widely distributed plant species. Little is known, however, about variation in stomatal distribution in the leaf epidermis and its correlation with the dimensions of conducting cells in wood. This study aimed at testing the hypothesis that Podocarpus lambertii, a conifer tree, possesses a well-defined pattern of stomatal distribution, and that this pattern can vary together with the dimensions of stem tracheids as a possible strategy to survive in climatically different sites.
Leaves and wood were sampled from trees growing in a cold, wet site in south-eastern Brazil and in a warm, dry site in north-eastern Brazil. Stomata were thoroughly mapped in leaves from each study site to determine a spatial sampling strategy. Stomatal density, stomatal index and guard cell length were then sampled in three regions of the leaf: near the midrib, near the leaf margin and in between the two. This sampling strategy was used to test for a pattern and its possible variation between study sites. Wood and stomata data were analysed together via principal component analysis.
The following distribution pattern was found in the south-eastern leaves: the stomatal index was up to 25 % higher in the central leaf region, between the midrib and the leaf margin, than in the adjacent regions. The inverse pattern was found in the north-eastern leaves, in which the stomatal index was 10 % higher near the midrib and the leaf margin. This change in pattern was accompanied by smaller tracheid lumen diameter and length.
Podocarpus lambertii individuals in sites with higher temperature and lower water availability jointly regulate stomatal distribution in leaves and tracheid dimensions in wood. The observed stomatal distribution pattern and variation appear to be closely related to the placement of conducting tissue in the mesophyll.
Stomata are pore-like structures located on the leaf surfaces of virtually all vascular, terrestrial plant leaves, and are responsible for the uptake of photosynthetic CO2, as well as for the potentially detrimental water loss (transpiration) from inside the leaf (MacDonald 2002). Thus, stomata play a primary role in regulating carbon uptake for growth and the prevention of plant desiccation (Apple et al. 2000; Croxdale 2000). Moreover, the frequency of these structures on leaf surfaces can dictate the degree of gas exchange potential for both photosynthetic CO2 uptake and transpirational water loss. In response to favorable environmental signals, stomata may open to facilitate carbon uptake, or close to prevent tissue drying and the maintenance of higher water use efficiency at different times of the growth season or given time of day (Croxdale 2000). Physical obstruction of these structures by a water film can strongly inhibit gas exchange (Brewer et al. 1991; Brewer and Smith 1997) and significantly decrease photosynthetic carbon gain by the plant (Brewer and Smith 1995). Water film coverage of stomata could be ever-present issue in the mountaintop spruce-fir forests of the Appalachian Mountains in the eastern United States, a region characterized by frequent cloud immersion and high humidity that would enhance water condensation on leaf surfaces. No studies to our knowledge have investigated the stomatal frequency on the leaf surface and hydrophobicity of leaves in the dominant conifer tree species P. rubrens and A. fraseri, and, thus, the potentially strong impacts on photosynthetic gas exchange and growth due to frequent cloud immersion. In the current study, we hypothesized that the recognized difference in altitudinal distribution of the dominant fir [Fraser fir, Abies fraseri (Pursh) Poir] and spruce (red spruce, Picea rubens Sarg.) trees corresponded to a difference in stomatal frequency and surface hydrophobicity between the two species and elevations. Fir is found in greater numbers at higher higher elevations where cloud-immersion is also more frequent (Braun 194). To test this hypotheses, the stomatal frequency (number per unit area) and surface hydrophobicity were measured in the spruce and fir at high and low elevation sites.
The stomatal patterns observed in this study are consistent with literature documenting the relatively large variety found in gymnosperms (Stockey and Taylor 1978, Croxdale 2000). These studies have also suggested that these stomatal patterns allow CO2 uptake in areas near internal mesophyll cells that perform photosynthesis (Croxdale 2000), possibly explaining the non-random distribution of stomata. The fact that stomata were observed exclusively within linear rows on needles in both species is similar to past investigations showing patchy stomatal patterns instead of homogenous configurations (Beyschlag et al. 1993). The fact that the fir and spruce species observed here had distinct stomatal patterns on the leaf surface suggests that the interior configurations of photosynthetic cells involved in gas exchange are also different. This relationship between stomatal pattern and connection to internal, photosynthesizing cells has not been investigated, to our knowledge, in any conifer species.
Our findings that stomatal frequency did not change for either species at the higher and lower elevation sites is contradicted by literature reporting a decrease in stomatal frequency at higher elevations in four dominant conifer tree species of the central Rocky Mountains, USA (Hultine and Marshall 2000). It is possible that the two field sites studied here were not different enough in altitude to cause differences in stomatal frequencies or θ. Stomatal frequencies between the spruce and fir needles were statistically comparable in samples collected at the high elevation site, but significantly different at the low elevation site. This finding is supported by past observations whereby variable stomatal densities were attributed to variability in microenvironmental conditions (MacDonald 2002). One such condition is the concentration of carbon dioxide in the atmosphere (MacDonald 2002; Kouwenberg et al. 2003), an environmental characteristic which decreases with greater elevation, along with corresponding decreases in stomatal frequency in conifer needles (Apple et al. 2000; Hultine and Marshall 2000; Kouwenberg et al. 2003).
The study on the morphology of stomata of conifers is the foundation of identifying fossil stomata that is important for the study of the change of vegetation and climate. In this paper, stomata of 3 genera 8 species of Pinaceae and 3 genera 4 species of Cupressaceae are studied by measuring reference stomata from fresh needles which prepared using the standard pollen preparation but without HF treatment.
The size of stomata is important criteria for separating Pinaceae and Cupressaceae. The stomata size, T-shape structure, the angle of attachment of the upper woody lamellae, are used together to distinguish among different genera. In genus, different species can be separated by observations such as the shape of the upper lamellae, the angle of the T-shape structure tail, stem width and length, medial lamellae border width and the outer brim of the upper woody lamellae of the stomata. A key to identify stomata is proposed.
Anatomical and morphological investigations of seven species of Iranian representatives of gymnosperms belonging to Taxaceae and Cupressaceae are performed in this study.
Transverse sections of leaves (needle-like or scales) were studied with a light microscope. Great anatomical variation exists between and within Taxaceae and Cupressaceae. Both families are easily distinguished from each other by anatomical characters.
All genera and species in Cupressaceae are also distinguishable. Fiber and resin ducts are present only in Cupressaceae and not in Taxaceae. In Cupressus sempervirens and Juniperus foetidissima, stomata are present only in the upper epidermis of scale-like leaves.
Stomata are present in lateral faces of needle-like leaves in Juniperus excelsa, J. sabina, J. communis and J. oblonga. In these species, stomata are present only in the abaxial epidermis where there are no fibers underneath the epidermis, a characteristic similar to that in Taxus baccata.
Juniperus communis and J. oblonga have stomata that are distributed uniformly in the lower epidermis, except under the midrib of J. oblonga, which is covered with fibers instead of stomata.