1. INTRODUCTION. Comparative anatomical and palynological studies. in angiosperas have witnessed a remarkable progress during

Transcription

1 1. INTRODUCTION Comparative anatomical and palynological studies in angiosperas have witnessed a remarkable progress during the last 100 years or so, largely because of their importance not only in establishing taxonomic and evolutionary relationships at different levels of taxonomic hierarchy, but also in understanding the adaptive significance of the variations encountered in different taxa (Svamy and Bailey 1949; Bailey 1951, 1957; Erdtman 1952; Howard 1959; Metcalfe 1961; Carlquist, 1967; Dickison 1969, 1972; Stebbins 1972, 1974; Rudall 198Gb),

2 2- Much of the affluence in the two conventional branches of botany (anatomy and palynology) is largely due to 1he application of modern tools such as SEM and TEM coupled with techniques such as histo and cytochemistry (Reichert,1913; Gibbs,19^5; Frost,1956; Bradley,1958; Stebbins and Zohary>1959; Heslop-Harrison, 1960; Nowaclfi, I960; Dormer, 1962; Heywood, 1969, 1971; Walker and Doyle, 1975; Walker, 1976a; Dickinson and Potter, 1976; Stebbins, 1977; Moore and Webb, 1978; Rudall, 1980a), Taxonomy-the oldest and conventional branch of botany is an unending synthesis of data obtained from different disciplines of biology solely with the objective of refining the circumscription and delimitation of taxa at different levels of taxonomic hierarchy. Such an 3 attempt definitely lead^to the development of a classification which has high predictability and practicability. This is exemplified by the system of classification proposed by Takhtajam (1980). Consequently, the utilization of anatomical and palynological data for taxonomic purposes is not altogether new either to taxonomy or to anatomy and palynology. Infact, Metcalfe and Chalk (195 ) clearly stated that the achievements of comparative anatomy are the solutions of cases involving misplaced' anomalous* or isolated genera. A similar view has been

3 -3- expressed by the leading palynologists such as Erdtman (1952) and Woodhouse (1935) n the role of palynological data in solving systematic and evolutionary problems* Stebbins (1974) is one of the strongest proponents for the utilization of morphological data in revealing and establishing evolutionary relationships* Comparative anatomical and palynological studies have been limited to only a small fraction of existing flowering plants (Frost, 1930; Tippo, 1938; Bailey, 1944; Money et al ; Hayes et al. 1951; Cheadle, 1953; Carlquist, 1957, 1961j Tomlinson, 1961} Shah, 1968; Nowicke et al. 1981). Extensive and intensive studies on the anatomy and palynology of specialized groups of evolutionary significance such as Amentiferae (Takhtajan, 1980), Ranales (Walker, 1976a) and Compositae (Cronquist, 1955; Burtt, 1960a) have been carried out. But detailed comparative anatomical and palynological studies on individual families are rather scanty or not at all available (Bass, 1972; Styer and Stern, 1979a, 1979b). Verbenaceae is one such family. Verbenaceae is predominantly a tropical family, and comprises 75 genera with over 3000 species (Heywood,

4 1978), The members Inhabit a wide range of habitatsaangroves to deserts and Itygji constituents of tropical forests to weedy communities. The growth form varies from small prostrate herbs (Phyla) to woody trees (Teetona). Economically the family is of considerable significance and includes the best tropical timber yielding trees such as (Teetona), and other medicinal and fire wood crop plants. Phylogenetically the family occupies a key position dicots with Verbenaceae of Verbnales. Further, the systematic position of some taxa is a subject of controversy wnd among taxonomists^ the circumscription and delimitation of taxa at different levels of taxonomic hierarchy is not always satisfactory. Consequently the family has attracted the attention of some recent taxonomists such as Moldenke (1973) who made drastic taxonomic changes within the family based on gross morphological characters. Except for a limited account on the anatomical features (Solereder, 1908; Metcalfe and Chalk, 1950; Xnamdar, 1969; El-Gazzar and Watson, 1970; Kannabiran, 1974; Lomibao and Silva, 1972; Meylan and Butterfield, 1974, 1978; Murty et al. 1978; Bhatt et al. 1979) and pollen morphology (Hair and Rehman, 1962; Saxena, 1973; Parabia, 1977) of a few representative members of the

5 -5- family, comprehensive account on the comparative anatomy and palynology of the family Verbenaceae encompassing a fairly large number of taxa is meagre. The present work was therefore, undertaken with the following objectives: i) To assess the extent of variation in qualitative and quantitative anatomical features of leaf, petiole and stem of different taxa, ii) To reveal the gross anatomical specializations in different taxa., iii) To record the diversity in pollen morphology of different taxa, iv) To utilise the observed patterns of variations in anatomical and pollen morphological features of different taxa in refining the circumscription and delimitation of taxa at different levels of taxonomic hierarchy by multivariate statistical analysis. v) To detect the evolutionary process responsible for the observed diversity in anatomical and pollen morphological characters, and to recognize certain evolutionary trends leading to specializations in relation to habitat.

6 -6- The results obtained in the present investigation have been discussed in the light of relevant published literature, keeping in view the realization of the objectives mentioned above.