SUMMARY AND CONCLUSIONS

Transcription

1 SUMMARY AND CONCLUSIONS J

2 CHAPTER VI SUMMARY AND CONCLUSIONS The significant modern trend in plant taxonomy is towards a synthesis between the older methods and outlook, and more recent developments in our knowledge of plants, regarding various aspects concern with classification. Recently the taxonomy has become a synthetic discipline incorporating data from different fields of Botany to accomplish the task well. Morphological characters are given more importance both for classification and for diagnostic purposes. Such characters can be seen easily. However, morphology must go hand in hand with other fields to establish phylogenetic relationships. In practice overwhelming reliance is placed on morphological characters or evidence, at least for expressing classifications, and even these have been largely restricted to the reproductive phase when dealing with angiosperms. According to Davis and Heywood (1991) often some characters are tend to be neglected which may be the "newer" kinds that are increasingly employed in recent years. Taxonomists still rely to a very large extent on morphological characters, both for producing classifications and for diagnostic purposes. According to Davis and Heywood (1991) many morphological features are in fact neglected and they may be vegetative or floral and there is a scope for further study. Comparative anatomical studies of angiosperms have achieved a remarkable record as anatomical characters have been employed with great success to the solution of difficult taxonomic problems. Anatomical structures are most likely to provide evidences concerning the inter-relationships of larger groups such as families and also helping to establish real affinities of their uncertain taxonomic status. The value of the character is measured for its constancy. The more constant the character, the greater is the reliability that can be placed upon it. Anatomical characters are more fixed than others. There are large number of anatomical

3 376 characters of systematic importance but "s pointed out by Metcalfe and Chalk (1950), the systematic anatomist must rely on those characters which are less plastic. They further suggested that conclusions supported by combination of characters are more reliable than those rest on a single character. Some important anatomical characters of well established taxonomic value are trichomes, stomata, epidermis, leaf architecture, histology of stem and petiole, sclereids, vessel elements etc. The first summary of the systematically more useful anatomical characters with an evaluation of their importance was provided by Fritsch (1903). Metcalfe and Chalk (1950, 1967, 1985) have enumerated a large number of anatomical characters of diagnostic value for different families. Bailey (1957) explained the potentialities and limitations of wood anatomy in the study of phylogeny and classification of angiosperms. The study of the morphology and ontogeny of the stomatal complexes in leaves has been one of the fruitftil areas for research. Several classification and types are recognized in stomatographic studies of flowering plants, for example, by Vesque (1889), Florin (1931, 1933), Smith (1935), Metcalfe and Chalk (1950, 1961), Van Cotthem (1970), Dilcher (1974), Baranova (1981, 1986, 1992), Christophel etal. (1996) and others. Butterfass(1987) discussed the value of study of orientation of stomata. The leaf architectural study is found to be useful for taxonomic purpose. Hickey (1971,1973,1979) provided leaf architectural classification in an elaborate manner for dicotyledons. Hickey and Wolfe (1975) provided first systematic summary of dicot leaf architectural features and they demonstrated that a number of lower order leaf architectural features, including leaf organisation, configuration of first three vein orders, and characteristics of leaf margin are significant systematic indicators within dicotyledons and to name a few recently, who studied leaf architectural features in different familes are Fuller (1995), Klucking (1995, 1997).

4 377 The shape of epidermal cells, thickness and characteristics of their wall, nature of sculpturing on their walls as seen in surface view, importance of papillate epidermal cells provide useful taxonomic criteria. Trichomes have been employed very frequently for systematic comparisons because of their diversity, their universal presence in the angiosperms and their ease of preparation. Several trichome types have been recognised. The two major categories are glandular and non-glandular and these are further subdivided on the basis of their gross form, cellular constitution, degree of branching etc. Solereder (1908), Netolitzky (1932) and Metcalfe and Chalk (1950) have provided useful information on the structure, function and classification of trichomes with their significance in comparative anatomical studies. They have proved more useful to taxonomists at generic and specific level. The aspect of classification and phylogeny of trichomes is discussed by Ramayya (1972). Their description and classification is also given by Theobald et al. (Metcalfe and Chalk's "Anatomy of the dicotyledons", Ed. 1973). One of recent articles is cited by Al-Shammary and Gornall(1994), Vascular system of dicot petiole, as seen in transverse section, is of considerable taxonomic importance. Several types of vascular structures of petiole are illustrated by Metcalfe and Chalk (1950). It is of much diagnostic significance along with other anatomical features of petiole. These characters have been used by Soladoye (1982) and Cutler (1982) for providing supportive evidence to be used in infra-generic classification of some genera. Internal structure of the primary (young) stem may provide useful diagnostic characters in many cases. Thorne (1992) states, "Another rich source of comparative information for phylogenists continues to be stem anatomical studies. There are several such significant anatomical characters including vessel elements, wood anatomy etc. Baranova (1992) states "Numerous unsolved

5 378 taxonomic problems have caused systematists to go beyond the methods of herbarium taxonomists and begin to use laboratory disciplines. The families of Tubiflorae of Engler have attracted the attention of many workers. There are extensive investigations in certain aspects of morphology and vegetative anatomy of some families of this group. However, in case of Verbenaceae some of the aspects are not extensively studied and thus, leave the scope for indepth study. Verbenaceae are comparatively a large family composed of about 98 genera and 2614 or more species (Lawrence, 1951). The name Verbenaceae was given by Persoon (1806) and has been conserved over older names as Pyrenaceae Vent (1799). In India it is represented by nearly 22 genera and more than 110 spp, some of the members being only grown as ornamentals. Verbenaceae is a widely distributed family of very diverse habit. They may be trees, shrubs or herbs; lianes occur fairly commonly, but no general distinctive habit is peculiar to the family as a whole. There is certain disagreement over the composition of Verbenaceae. Certain genera included by Engler in Verbenaceae are excluded by some workers from this family or some genera included. The monotypic genus Phryma was placed in Phrymaceae by Engler. However, Hutchinson broadened the circumscription of f Verbenaceae to include the Phrymaceae and segregated it from Lamiales in 1948 as Verbenales. Moldenke (1946) following Endlicher (1841), Eichler (1878) and others, accepted Avicenniaceae as a family distinct from Verbenaceae on the basis of wood anatomy and certain other characters. Not only Avicenniaceae but some other families like Chloanthaceae, Dicrastylidaceae, Stilbaceae, Symphoremataceae etc are recognized as distinct families containing certain genera included in Verbenaceae by Engler. Thorne (1992) placed Verbenaceae in Lamineae composed of only Verbenoideae. He not only recognized Phrymaceae, Symphoremataceae,

6 Nesogenaceae, Avicenniaceae as distinct families but placed Chloanthoideae including Tectona L. in Lamiaceae. There is also certain discussion regarding systematic position of Nyctanthes L., some favouring its inclusion in Verbenaceae. However, most workers consider Verbenaceae and Labiatae closely related. Even Wernham (1912) placed the families Labiatae, Verbenaceae and Myoporaceae together in the Diovulatae of Tubiflorae. Takhtajan (1985) considers Lami^aceae very closely related to the Verbenaceae and the taxonomic boundary between the Lamiaceae and Verbenaceae not clear cut. Anatomy has helped to a great extent in clarifying confusions which arose in the systems deviced by classical taxonomy. Considering the importance of morphological and anatomical studies, 18 species of Verbenaceae for representing 12 genera were selected for the present work, have been studied. These genera are arranged as per Benthan and Hooker system of classification ( ). Tribe Verbeneae - Lantana camara L. var. aculeata (L.) Mold, L. camara L var. nivea Bailey, L. camara var. flava Moldenke, Phyla nodiflora (L.) Greene, Stachytarpheta jamaicensis (L.) Vahl, S. mutabilis (Jacq.) Vahl, Verbena bipinnatifida Schau,, Petrea volubilis L., Duranta erecta L. Tribe Viticeae - Tectona grandis L.f, Gmelina arborea Roxb., G. philippensis Cham., Vitex negundo L., Clerodendruminerme (L.) Gaertn., C.multiflorum (Burm.f) O.Ktze., C.serratum (L.)Moon., C.splendens G. Don, C. viscosum Vent, Holmskioldia sanguinea Retz. Some workers had suggested inclusion of Nyctanthes arbor-tristis L, in Verbenaceae. Therefore it was also studied. The thesis that \s to be submitted is emboding significant data collected in respect of plants mentioned above regarding; 1) The external morphological charact^s of the aerial plant parts, 2) Anatomy of young stems (transections) in details, 3) Petiole anatomy (base, middle and apical region).

7 380 4) Leaf architecture: nature of primary, secondary and tertiary veins, angle of divergence, angle of origin of tertiary on admedial and exmediai side, major venation pattern, marginal ultimate venation, areole study with veinlets, ending nature of vein inside teeth, intersecondary and intramarginal veins, special types of glands or nectaries etc 5. Epidermal characters in relation to : A. Stomatographic studies - in relation to type, shape, orientation, frequency, dimensions, etc, present on stem, petiole, peduncle, pedicel; abaxial and adaxial surface of leaf, bract, sepals and on corolla tube and lobes and fruit. B. Epidermal cells - size, shape, orientation, wall character, cuticular striations of cells etc. of stem, petiole, leaf (abaxial and adaxial), bracts (abaxial and adaxial), peduncle, pedicel, sepals (abaxial and adaxial), corolla tube and lobes, stamen, carpel and fruits. C. Trichomes - glandular or non-glandular their type, length, breadth form, wall characters, surface, contents, basal and apical characters, seat and adjoining cells, degree of branching, component cells etc. on stem, petiole, peduncle, pedicel and on abaxial and adaxial surfaces of leaf, bract, sepals, outer and inner surface of corolla tube and on corolla lobes, filaments, anther, ovary, style, stigma and fruit. 6. Study of vessels: length and breadth, type of perforation plate, size and position; pitting type - distribution, pattern, size, etc. The plant materials for this study of the naturalized taxa were collected from different habitats around Amravati. Material of Tectona grandis was collected from Amravati and Melghat forest where Teak is the most dominant component of the forest associations. Clerodendrumviscosum was collected from Chikhalda, the only habitat for this plant in Vidarbha. Materials of the ornamental taxa were collected from various gardens at this place. The study of characters of epidermal cells, trichomes and stomatography was made by preparing suitable micropreparations of epidermal peels or whole organs or their parts. Wherever necessary, epidermal peels were separated by clearing technique using sodium hydroxide. Mature fresh leaves or herbarium

8 381 material was used for the study of leaf structure. Standard methodology involving use of sodium hydroxide of 5-10% strength and 5% glacial acetic acid was followed. The terminology of Hickey (1973) and Baranova (1992) for describing leaf architecture and stomatal complex is followed respectively. Jeffrey's method was followed for study of wood vessels of the stem. All the materials and micropreparations are properly preserved Microtome sections were taken where felt necessary. Camera lucida sketches are drawn for all the characters observed. Photographs for certain characters are also taken. The text of the thesis has been arranged according to the conventional practice of chapterization. It is organised into chapters like Introduction, Review of Literature, Material and Methods, Morphological and anatomical descriptions of the characters of taxa studied. Discussion and General Considerations, Summary and Conclusions followed by Bibliography. Dichotomous keys using morphological and anatomical parameters for identification of taxa studied, tables, figures, their explajiation, plates bearing photographs etc. are given at appropriate places. As far as possible, the description of variation of one anatomical characteristic and the correlation between pairs or groups of anatomical characteristics are given. Metcalfe and Chalk (1950, 1985) have enumerated several diagnostic anatomical features of Verbenaceae. Many of such characters have been recorded during the course of this study for different plants selected for study. For example. Glandular hairs in Lantana camara, Stachytarpheta jamaicensis, Vitex negundo, Clerodendrum spp.etc. Ranunculaceous stomata in C.multiflorum, N. arbor-tristis, Clerodendrum inerme, Gmelina philippemis etc. Caryophyllaceous stomata in Clerodendrum serratum, C. splendens, Phyla nodiflora etc. Cruciferous type of stomata in Clerodendrum viscosum, Gmelinaphilippensis. etc. Medullary vascular bundles enclosed within the main petiolar vascular strand in Lantana camara, Duranta erecta, Vitex negundo etc. Single median crescentic vascular strand in

9 382 petiole of Phyla nodiflora, Stachytarphetc jamcicemis, Gmelina philippemis etc. Cylindrical vascular strand in petiole of Petrea volubilis. Vessels mostly with simple perforation plate, lateral walls mostly with simple circular pits, fine spiral thickening in Phyla nodiflora etc. A very brief mention of the characters observed is being made here to indicate the nature of work that has been carried out. For the anatomy of young stem, the characters observed the nature of cuticle, trichomes, epidermis, cortex, endodermis, pericycle, phloem, cambium, xylem vessels, pith etc. The transectional outline in most of the taxa is quadrangular with elaborate ribs at 4 corners, quadragular-roundish as in Petrea volubilis, Duranta erecta, Gmelina philippensis, Clerodendrum inerme etc. and hexagonal in Clerodendrum serratum. Cuticle in majority of taxa is moderate thick and trichomes are present in all, they are medifixed and adpressed in Phyla nodiflora, branched in Tectona grandis, Gmelina arborea. The epidermis is silica impregnated in Petrea volubilis. The outer and inner walls of epidermal cells are variable. The cortex mostly divisible into outer couenchymatous and inner parenchymatous chlorophyllose; couenchymatous mostly discontinuous and it is continuous»" Stachytarpheta mutabilis, Petrea volubilis, Duranta erecta, Clerodendrum splendens, C. viscosum, it is narrowest in Duranta erecta and broadest in Tectona grandis, accompanied by stone cells in Tectona grandis and Clerodendrum inerme, inner cortex mostly normal, narrowest in Lantana camara var, aculeata, broadest in Tectona grandis; with prominent intercellular spaces in Phyla nodiflora; accompanied with stone cells in Tectona grandis^celh containing acicular crystals in Gmelina arborea, with 4 inverted cortical vascular bundles in 4-corners in Nyctanthes arbor-tristis. Pericycle mostly heterogeneous, almost composite in Petrea volubilis and Tectona grandis. Vessels are mostly with simple perforation plates, lateral walls with simple

10 circular pits, fine spiral thickening observed in Phyla nodiflora. 383 The vessels are very long in Stachytarpheta jamaicencis while they are short in Tectona grandis. They are broad in Clerodendrum inerme and narrowest in Phyla nodiflora. Regarding petiolar anatomy, a single median crescentic vascular strand observed in Lantana camara var. aculeata, L. camara var. flava, L. camara var. nivea. Phyla nodiflora, Stachytarpheta jamaicensis, S. mutabilis. Verbena bipinnatifida, D. erecta, G. philippensis, Vitex negundo, Clerodendrum inerme, Holmskioldia sanguinea and Nyctanthes arbor-'iristis These strands may be either deep or shallow with widely placed or incurved ends. The vascular strands are single meduliated completely closed cyunder observed in Petrea volubilis, open dissected arc of vascular bundles in Clerodendrum multiflorum, C. serratum, C. splendens and almost closed dissected arc in Tectona grandis, Gmelina arborea and Clerodendrum viscosiim. The major venation pattern is pinnate Craspedodromous and Semicraspedodromous observed in Lantana camara var. aculeata, L. camara var. flava, L. camara var. nivea. Phyla nodiflora, Stachytarpheta jamaicensis, S. mutabilis and Duranta erecta. The highest vein order of the leaf is 5 observed in Lantana camara var aculeata, L. camara var. nivea and Phyla nodiflora. These species are separated from each other on the basis of tertiary angle of origin on exmedial and admedial side. The remaining 4 species of this group such as Lantana camarawar. flava and Duranta erecta are separated on the basis of marginal ultimate venation. The remaining 2 species of this group Stachytarpheta jamaicensis and.s". mutabilis, are separated on the basis of accessory veins of tooth. The type of venation is pinnate Comptodromous Brochidodromous observed Tectona grandis, Gmelina philippensis, Vitex negundo, Clerodendrum inerme, C. splendens, C. viscosum. All these species are separated from each other on the basis of highest vein order of the leaf, tertiary vein angle and orientation of quaternary veins.

11 384 The detail study of organographic stomatal complex has been carried out. Among the taxa studied, Lantana camara var. aculeata, L. camara var. flava, L. camara var, nivea. Phyla nodiflora, Stachytarpheta jamaicensis, S. mutabilis. Verbena bipinnatifida of tribe Verbeneae and Clerodendrum multiflorum of tribe Viticeae are charactrised by amphistomatic leaves; Petrea volubilis, D. erecta of tribe Verbeneae and Tectona grandis, Gmelina arborea, G. philippensis, Vitex negundo, Clerodendrum inerme, C. serratum, C. splendens, C. vrscosum, Holmskioldia sanguinea of tribe Viticeae and Nyctanthes arbor-tristis are characterised by hypostomatic leaves. Corolla lobes are astomatic in Stachytarpheta jamaicensis, S. mutabilis, Tectona grandis, Vitex negundo, Holmskilodia sanguinea and in rest of the taxa they are hypostomatic. They are characterised by only anomocytic type of stomata except in Clerodendrum serratum they are diacytic. Various abnormal stomata distributed among the taxa studied are recorded viz. Clerodendrum inerme, Gmelina philippensis and some others. These are categorised into major types as contiguous stomata, stomata connected by cytoplasmic bridge, stomata with single guard cell, degenerated stomata, stomata with arrested development etc Epidermal cells as seen in surface view, may be of different types in different organs or even on different faces of same organ in same species. They are straight, sinuous with various degree of sinuosities, wavy or papillate. In Petrea volubilis they are uniformly papillate on all the organs. Regarding cuticular striations, they show their various patterns on different organs of various taxa. In the present investigation, the trichomes were observed of many diverse types both non-glandular and glandular in various taxa studied. The detail study regarding their organographic distribution, type, base characteristics, dimensions etc. is carried out. They occur on most of the organs and in all the taxa studied. Each taxon having specific type though differing organwise in some minor

12 385 characteristics. Combination of different trichomes may occur on same organ or they may be of different types on different surfaces, may be present on one and absent on other in bifacial organs. Floral trichomes may be diflferent from vegetative ones in same taxon suggesting their functional significance. On the basis of their varied structure, broadly six types of non-glandular and two types of glandular trichomes are recognised which fall into subcategorisation. Staminal glandular trichomes are very typical and unique in Gmelina arbora and G. philippensis. Floral glandular trichomes are special and typical for particular taxon and particular organ as corolla trichomes in Stachytarpheta jamaicensis, S. mutabilis, Petrea volubilis, Duranta erecta etc. or staminal trichomes in Gmelina arborea, G. philippensis, Holmskioldia sc^uinea etc. The trichomes noticed in the studied species are not only of morphological value but also of taxonomic significance and are useful in distinguishing genera and species. The major categories in majority of taxa are unicellular conical, and uniseriate multicellular non-glandular trichomes. Unicellular medifixed 2 armed non-glandular observed in Phyla nodiflora. Stellate branched in Tectona grandis. Glandular trichomes are either short stalked, long stalked or peltate with 1-few celled, globose or spherical head containing hyaline or dense contents. On the basis of detailed study of trichomes, a diagnostic key has been constructed, separating all the 20 taxa. Quantitative features regarding stomatal frequency, size, stomatal index etc., vessel length and breadth; quantitative features of petiolar anatomy are given in various Tables presented in Chapter of Discussion and General Considerations. The Verbenaceae and Lamiaceae are a closely related pair of families. Most authors agree that the Lamiaceae represent the realization and culmination of trends that begin in the Verbenaceae. The boundary between the two families is arbitrary and merely conventional. The Verbenaceae are diverse in habit and gynoecial structure, and several peripheral groups have often been extracted as distinct

13 386 families notably Avicenniaceae, Chloanthaceae, Phrymaceae, Stilbeaceae and Symphoremataceae. Their relationships are not in dispute, and taxonomic rank at which they should be recognised is purely a matter of test (Cronquist, 1988). He felt reduction of them to less than familial rank. Findings from present work have been discussed with known literature and support Verbenaceae as a natural group, in which intergeneric differences are clearly defined and in majority of findings there is parallelism in morphological and anatomical characters. Hence, to conclude the present research work, it is seen that all the plants taken for study, having common characteristics, however, there are some plants which share the characters of the plant species of different families. In addition to that, they have their own specific characters which are uncommon to the plants of same family. To discuss the position of plants such as Nyctanthes, more work on modern line of research is needed to come to concrete suggestion. It also indicates that the study of morphological and anatomical characters of all the members of Verbenaceae can be useful along with embryological, cytological, palynological, chemotaxonomic data even to the extent of molecular level in solving some of the problems of systematics of this family. Data obtained from a study like the present one can be useful for conclusions based on comparative anatomy.