The present investigation explores and compares the detailed anatomical features of an emergent aquatic herb of Monochoria vaginalis and Monochoria hastata, belonging to water-hyacinth family, Pontederiaceae. These weedy plants are claimed to be highly nutritious and medicinally valuable among many ethnic communities throughout India. But due to their morphological similarity among the related species of this family, identification and utilization of the plant has been ignored and urbanization has resulted in eradication of the herb on the basis of environmental wet land pollution issues.
Both species exhibits unique hydromorphic anatomical features related to the adaptability of the plant to the aquatic environment. Though both species share most of the anatomical features in common, few differences observed in the leaf anatomy like dorsiventral lamina, brachy-paratetracytic stomata of M. vaginalis and isobilateral lamina and paracytic or cytocytic stomata of M. hastata will provide valuable information for the plant identification.
Even though both the species share common morphological features in common which make them difficult to identify, the microscopical variations observed from the current report helps in identification and will meet the demand of standardization requirements of medicinal herbs.
Epidermal cells and stomata Monochoria vaginalis: Para dermal sections were used for studying the stomatal type and epidermal cells. The stomata are present on both upper and lower sides of the lamina. The stomata are brachy-paratetracytic type (Fig. 2d). A stoma has two lateral subsidiary cells and two larger polar subsidiary cells situated on the upper and lower poles of the guard cells. The guard cells are oblong, elliptic measuring 20×50 μm in size. The epidermal cells are fairly thick walled, angular and compact (Fig. 2e).
Monochoria hastata: Stomata occur on both the upper and lower surfaces of the lamina. They are diffused and random in distribution. The stomata are either paracytic or cytocytic, the former being more in frequency (Fig. 2j), the paracytic stoma has two wing like subsidiary cells, one on either side of the guard cells and parallel to the guard cells (Fig. 2k). In the cytocytic type, a stoma is surrounded by four subsidiary cells, two cells being polar and other two being lateral in position.
Water hyacinth (Eichhornia crassipes (Mart.) Solms) is a prolific free floating aquatic macrohpyte found in tropical and subtropical parts of the earth.
The effects of pollutants from textile wastewater on the anatomy of the plant were studied. Water hyacinth exhibits hydrophytic adaptations which include reduced epidermis cells lacking cuticle in most cases, presence of large air spaces (7~50 μm), reduced vascular tissue and absorbing structures.
Textile waste significantly affected the size of root cells. The presence of raphide crystals was noted in parenchyma cells of various organs in treated plants.
Epidermal peels of leaves were studied. Trichomes are not observed in epidermis.
Stomata are of paracytic type. The average size of guard cells was calculated to be 7 µm×4 µm, while the average size of the pore was 4 µm×4 µm. The stomata frequency on the upper epidermis was 2.83 mm2 and 3.32 mm2 on the lower epidermis. Thus the leaves are amphistomatic (Figs.(Figs.1010~~11).11).
Stomatal characteristics of epidermis in control and experimental plants are given in Tables Tables55~~6.6. The experimental plants showed significant (P<0.05) reduction in the size of upper and lower epidermal cells, while the stomatal frequency and stomatal index in upper epidermis were not significantly affected.
On the basis of the shape and size of the outer stomatal ledge, 153 species of the genus Dendrobium (Orchidaceae) were divided into three groups, i.e., species group I, species group II, and section Grastidium.
Student’s t-test and principal components analysis using seven stomatal characters suggest that the first two groups are quite distinct from each other. The values for section Grastidium, however, are scattered and indicative of heterogeneity.
Our data suggest a high probability that species groups I and II are monophyletic sister groups. However, section Grastidium, in which stomatal diversification has occurred, may be para- or polyphyletic relative to the genus Dendrobium.
Brazilian species of the genus Epidendrum, distributed over various habitats, were analysed for epidermal structure to test correlations between habitat form and variation in stomatal parameters.
This study confirmed the tendency for stomatal index values to increase in the apical direction of the foliar surface in this genus. The generally held view that there are a smaller number of stomata on the adaxial surface in amphistomatic leaves was contradicted for E. vesicatum, whose pendent sympodia showed that the adaxial foliar surfaces assume the abaxial position in relation to light incidence.
Both leaf attributes and stomatal traits are linked to water economy in land plants. However, it is unclear whether these two components are associated evolutionarily.
In characterizing the possible effect of phylogeny on leaf attributes and stomatal traits, we hypothesized that a correlated evolution exists between the two. Using a phylogenetic comparative method, we analyzed 14 leaf attributes and stomatal traits for 17 species in Paphiopedilum. Stomatal length (SL), stomatal area (SA), upper cuticular thickness (UCT), and total cuticular thickness (TCT) showed strong phylogenetic conservatism whereas stomatal density (SD) and stomatal index (SI) were significantly convergent. Leaf vein density was correlated with SL and SD whether or not phylogeny was considered. The lower epidermal thickness (LET) was correlated positively with SL, SA, and stomatal width but negatively with SD when phylogeny was not considered. When this phylogenetic influence was factored in, only the significant correlation between SL and LET remained.
Our results support the hypothesis for correlated evolution between stomatal traits and vein density in Paphiopedilum. However, they do not provide evidence for an evolutionary association between stomata and leaf thickness. These findings lend insight into the evolution of traits related to water economy for orchids under natural selection.
Leaf anatomy was investigated in six epiphytic orchids under Orchidaceae family. Five species of orchids such as Acampe praemorsa, Aerides ringens, Bulbophyllum sterile, Dendrobium aphyllum and Oberonia brachyphylla were studied.
Anomocytic stomata were recorded and stomatal index ranges from 7.69% to 28.6%. The minimal stomatal index was recorded in Dendrobium aphyllum (7.69%) where as maximal is in Acampe praemorsa (28.66%).
The number of stomata in a definite area of leaf varies from plant to plant. Low value of stomatal index is an adaptation of orchid plants to survive in different climatic conditions by conserving water. A detailed study is needed to reveal these differences in stomatal density.