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REVIEW OF LITERATURE
The epidermis represents the covering layer of a plant’s primary body. It constitutes one of the fundamental tissue systems. It is much more diversified structurally and functionally than other two tissue systems. The epidermis is distinguished into three components: The epidermal cells, stomata and trichomes (Esau, 1965).
The application of anatomical characters in plant classification dates back to Bureau (1864). For the first time Bureau (1864) used anatomical characters for the delimitation of taxa within the family Bignoniaceae.
Strasburger (1866) and Hildebrand (1866) are among the pioneers in the study of stomatal complex.
Weiss (1867) was perhaps the first botanist to classify and describe the different types of hairs. Though studies on the epidermis have been receiving the attention of botanists since 19th century, the worthy information was given by Solereder (1908) in his two volumes on “Systematic Anatomy of Dicotyledons.”
Several isolated publications on the structure and development of epidermal tissue appeared (Florin, 1931, 1933; Rao, 1939; Netolitzky, 1932; Miller, 1938; Hemenway and Allen, 1936) in the next four decades.
In 1950, there was a revival of interest in the anatomical studies with the publication of a monumental review work in two volumes by Metcalfe and Chalk. These volumes exhaustively reviewed the earlier works on the anatomical characters including leaf epidermis. Later on a number of plant anatomists worked on this epidermal tissue system, which dealt on the possible uses of anatomical evidence in the study of phylogeny and classification of plants.
Several classifications of stomata were made by various morphologists based on their mature structure, ontogeny or both. A review of literature reveals that Prantl (1872, 1881), Vesque (1889), Florin (1931, 1933), Metcalfe and Chalk (1950), Metcalfe (1961), Stace (1965a), Payne (1970, 1979), Van Cotthem (1970), Patel (1979) and Ramayya and Rajagopal (1980) classified stomata using different parameters.
Baranova (1987) brought out the historical development of the present classification systems of morphological types of stomata.
Prantl (1872) was the first botanist to classify the stomata into two ontogenetic types – direct and indirect types.
Prantl (1881) classified fern stomata into three types, “Stomata libera,” “Stomata applicata,” and “Stomata suspensa.”
Vesque (1889) distinguished four types of stomata. They are named as Ranunculaceous, Rubiaceous, Caryophyllaceous and Cruciferous on the basis of the families in which each type was observed for the first time.
Florin (1931, 1933) classified the stomata of gymnosperms into two ontogenetic types haplocheilic and syndetocheilic, which were later replaced by terms “perigenous” and “mesogenous” respectively.
Metcalfe and Chalk (1950) substituted the new terms for Vesque’s as follows – ranunculaceous – anomocytic, cruciferous – anisocytic, caryophyllaceous – diacytic and rubiaceous – paracytic in order to make the impression that they are not found only in the representative families but also in other taxa as well. Subsequently actinocytic, tetracytic (Metcalfe, 1961) and cyclocytic (Stace, 1965a) types were added to this existing types.
Ramayya and Rajagopal (1980) had studied 500 angiosperms and classified the subsidiaries according to their spatial relationships into the following seven types. 1. Common subsidiary (c-type) 2. Abutting subsidiary (a-type) 3. Free subsidiary (f-type). 4. Common – Free subsidiary (cf-type) 5. Common – Abutting subsidiary (ca-type) 6. Abutting – Free subsidiary (af-type) 7. Common – Abutting – Free subsidiary (caf-type)
Leaves with their various anatomical features including epidermis, stomata and hairs have provided increasingly valuable diagnostic tools in taxonomic consideration and in tracing the phylogeny. Distribution, size and types of stomata have been considered as a potential taxonomic tool and reported to be specific for a genus and species (Miller, 1938).
In his exhaustive studies carried out on the leaf epidermis of several members of Acanthaceae Ahamad (1972, 1974a.b; 1975, 1976, 1979) stressed the taxonomic and diagnostic importance of stomata and hair in finding a solution to the controversy existing in the systematic position of several subfamilies of Acanthaceae.
Paliwal (1967) studied the structure and ontogeny of stomata in Acanthaceae and found that in Elytraria and other Acanthaceae members stomata are diacytic and development is syndetocheilic but in Scrophulariaceae stomata are anomocytic and development is haplocheilic. Hence Paliwal (1967) retained the genus Elytraria in the family Acanthaceae.
Paliwal and Bhandari (1962) studied the stomatal development in some Magnoliaceae and found syndetocheilic development in the leaves.
In a series of research papers (1965a,b, 1966, 1969, 1973), Stace brought out the significance of leaf epidermis particularly the peltate glandular hairs in the taxonomy of Combretaceae.
Inamdar (1969a) studied the stomata of Nyctanthus and expressed the opinion that this genus should be kept in Oleaceae. In Nyctanthus and Oleaceae the stomata are tetra-mesoperigenous while Verbenaceae shows dia-mesoperigenous. On this basis Inamdar (1969a) included Nyctanthus in Oleaceae instead of Verbenaceae.
Inamdar and Chohan (1969) studied epidermal structure and stomatal development in Malvaceae and Bombacaceae. The mature stomata are anomocytic, anisocytic and paracytic in the members of both the families,
Inamdar and Bhatt (1972) studied the structure and development of stomata in some Labiatae. They reported diacytic, anomocytic and paracytic stomata. Abnormal stomata with single guard cell, arrested development and contiguous stomata have been observed.
Kannabiran and Ramaswamy (1988) studied the mature epidermis and stomatal ontogeny in the leaves of ten species belonging to Apocynacesae. They observed four stomatal types viz. anomo-, aniso-, tetra-, and paracytic occur in different combination pattern. They reported that codominance of two stomatal types and their origin from unilabrate meristomoids isolate Catharanthus from other taxa like Wrightia, Ervatamia, Carissa etc.
Kotresha and Seetha Ram (2000) studied and compared the epidermal micromorphology of some species of Cassia (Caesalpiniaceae). The leaves are either hypo or amphistomatic and possess para-, aniso-, tetra-, and anomocytic type of stomata. The trichomes are uni or multicellular. A key based on epidermal characters is provided for the identification of Cassia species.
Jelani et al (1990) studied the foliar epidermis in Indian species of Cleome and prepared a key for identification of the species studied.
Several botanists including Stebbins and Shah (1960), Stebbins and Jain (1960), Stebbins and Khush (1961), Tomlinson (1965a, 1965b), Pant and Kidwai (1966), Inamdar (1968a) and Shah and Gopal (1970) described stomata and their ontogeny on the leaves of monocotyledons.
The most extensive study was that of Stebbins and Khush (1961) who examined the organisation of stomata on the leaves of 192 species belonging to 49 families. The eight types of stomata commonly found in the monocotyledons are anomo- para-, tetra-, hexa-, cyclo-, tri-, dia-, and anisocytic (Nirmala Upadhyaya and Trivedi, 1987).
With their exhaustive research work Prabhakar et al. (1984) described the structure and distribution of the elements of epidermal cell complex in angiosperms. Variation in epidermal cell characters viz. shape, anticlinal and perclinal walls, cytoplasmic contents, sculpturing of outer wall, arrangement and orientation have been presented.
Studies in Faboideae
With their exhaustive series of publications on epidermal structure and ontogeny of stomata, Shah and Gopal (1969a,b,c); Shah and Kothari (1973, 1974, 1975, 1976) emphasized that it is possible to segregate genera within the tribes in the family Papilionaceae.
Shah (1968) studied the development of foliar stomata in Dolichos lab-lab, D. biflorus, Vigna capensis, Phaseolus aconitifolius and Atylosia platycarpa and reported paracytic stomata as more frequent type than the anisocytic ones.
Shah and Gopal (1969a) studied the ontogeny of stomata on foliar and floral organs of eight species of Crotalaria. According to them in Crotalaria the paracytic stomata are by far the commonest followed by anisocytic and anomocytic ones.
Shah and Gopal (1969b) studied the ontogeny of stomata in 20 species of Papilionaceae. In all these mature stomata may be paracytic, anisocytic, anomocytic, diacytic or with one subsidiary cell.
Shah and Gopal (1969c) reported paracytic stomata as common type in leaves of Vigna unguiculata, Phaseolus radiatus and P. aconitifolius which support the inclusion of the species in the tribe Phaseolae.
Shah and Kothari (1973) studied the structure of stomata and hairs in ten species of tribe Vicieae (Papilionaceae) where they show diversity of stomata but more frequently anomocytic and development is mesogenous or mesoperigenous. Hairs may be glandular or eglandular.
Shah and Kothari (1974) studied the epidermal structure in six species of tribes Sophoreae and Podalyrieae and reported anomocytic stomata as most frequent type and anisocytic ones are extremely rare and uniseriate eglandular hairs are common types of trichomes.
Kothari and Shah (1974) reported paracytic stomata as dominant type in tribe Dalbergieae by studying 13 species belonging to four genera. The taxonomic use of these epidermal characters at generic level is suggested by them.
Kothari and Shah (1975) studied the epidermal structure and ontogeny of stomata in tribe Hedysareae of Papilionaceae. The most frequent type of stomata is paracytic in all genera except in Zornia where it is anisocytic. Uniseriate eglandular hairs are common type.
Shah and Kothari (1975) studied the structure of stomata, hairs and stomatal ontogeny in 12 species of the tribe Trifolieae of Papilionaceae. The most frequent types are paracytic, anisocytic and anomocytic and haplocytic. They also generalized in this tribe that anomocytic stomata are more frequent on both surfaces of leaflets and paracytic on stem and petiole, but stomata show diversity, they are oflittle value for diagnostic purpose.
Shah and Kothari (1976b) studied the stomatal morphology in 20 species of tribe Galegeae of Papilionaceae and reported that stomata can be used to a limited extent as a character to delineate genera, i.e. (1) Stomata predominantly anomocytic – Astragalus, Caragana, Cyamopsis, Indigofera, Mundulea. and Sesbania, (2) Stomata predominantly paracytic – Gliricidia, Millettia, Psoralea and Tephrosia.
Shah and Kothari (1978) described the stomata and trichomes and stomatal ontogeny in 46 species of Phaseoleae tribe. Stomata may be paracytic, anisocytic, anomocytic and haplocytic, the first type being the most frequent.
Kannabiran (1975a) studied the structure of mature epidermis and the stomatal ontogeny on vegetative and floral organs of Zornia diphylla and Zornia zeylonensis.
Kannabiran (1975b) in his paper discussed the stomatal ontogeny and systematic position of Abrus precatorius and recommended the inclusion of Abrus in the tribe Phaseoleae instead of Vicieae.
Leelavathi (1976) in her study on the stomatal structure and development along with other epidermal characters of leaf (lets), stipels and stipules of 105 species of the Leguminosae (3 sub-families) described the stomatal distribution pattern and costal cell distributional pattern in Leguminosae and their taxonomic significance.
Leelavathi et al (1980) described the foliar stomatal distribution pattern in Leguminosae and their taxonomic significance.
Vijayakumar (1988) studied the foliar epidermal features in some endemic taxa of Indigofera and showed their significance in taxonomic delimitation.
Subba Rao and Shanmukha Rao (1994) carried out studies on structure, distribution and taxonomic importance of stomata in some Indian Tephrosia (Fabaceae) and brachy paracytic stomata have been recorded for the first time.