Role of following branches of Botany in Taxonomic evidence: Morphology, Anatomy, Palynology, Embryology, Cytology, Phytochemistry, Nucleic acid hybridization as a tool in taxonomy

Role of following branches of Botany in Taxonomic evidence: Morphology, Anatomy, Palynology, Embryology, Cytology, Phytochemistry, Nucleic acid hybridization as a tool in taxonomy:-

Role of Morphology in Taxonomic evidence:-

> It mainly deals with the external characters of the plant such as: Habit, Root structure, Stem structure, Stem habit, Bud structure, Leaf structure, Inflorescence type, Flower type, Perianth structure, Androecium type, Stamen character, Gynoecial type, Carpel structure, Ovule type, Fruit type and Seed type.

> Traditional taxonomy considers the morphological character only as useful evidence. It provided the basic language for plant characterization, classification and identification etc. Morphological data is useful in taxonomic studies.

> Bark characters are of significance in Pinus to identify species. Hutchinson considered habit as important character. Member of Orchidaceae are herbaceous. Members of Fagaceae are woody. The characteristics feature of Allium is presence of bulb while that of Iris is rhizome, Stolon is found is Fragaria. Davis (1960) divided Turkish species of subgenus Ranunculus of genus Ranunculus on the basis of habit.

> Previously it was thought that trees and shrubs with simple leaves represent the most primitive condition of angiosperms but now it is believed that the perennial herbaceous condition in Paleoherbs (Ceratophyllaceae, Nymphaceae, and Piperaceae etc.) is the archetype of the most primitive angiosperms.

> Pitcher shaped insectivorous leaves are characteristic of Saracenia, Napenthes and that of non insectivorous Dischidia. Tentacular leaves are typically found in Drosera. Salix and Populus are differentiated on the basis of leaves.

> Azadirachta and Melia are separated on the basis of leaf type (Uni-and Bipinnate), leaf venation and type of stipule are also very important morphological character e.g., Viola, Lathyrus and members of Rubiaceae etc.

Role of Anatomy in Taxonomic evidence:-

> Anatomy is the study of the structure; organization and development of plant cell and tissue. It is basically related to the internal structure.

> The evidences come from: Wood cell type, size and shape, Wood cell wall sculpture, pattern, Stealer pattern, Vascular bundle type, Xylem type, wood type and ray type, Ground tissue type, Epidermal type, Mesophyll type, Scleried type, Stomatal type, Trichome type, crystal type, Nodal type, Ventation type, Petiole vasculation type, Periderm origin, Pholem cell type and Specialized cell type.

> The application of anatomical data to phylogenetic problem is of great value in elucidating taxonomic relationships.

> Nonporous wood is the characteristic feature of gymnosperms while porous wood is found in angiosperms. Anatomical work of taxonomic significance was mainly dealt by Bailey et. al. Carlquist (1996) described the trends of xylem evaluation in the context of primitive angiosperms. Wood is nothing but the secondary xylem consisting of xylem Tracheids, vessels, parenchyma etc.

> It is believed that there is a progressive evolution in angiosperm from small tracheids to long narrow vessels with lignified thickening of various types. Wood anatomy reveals that Gnetales are not ancestral to angiosperms and Amentiferae constitute a relatively advanced group.

> It was Bailey (1940) who suggested that in Gnetales the vessels arose from tracheids with circular pittings while in angiosperms they evolve from tracheids with scalariform pitting. Vesselless angiosperms like members of Winteraeae, Trochodendraceae Tetracentraceae etc., show that primitive angiosperms were vesselless. Uniseriate and homocellular rays are found in Populus while multiseriate and heterocellular in Eupomatia.

> Wood anatomy supports the separation of Austrobaileya and Paeonia to separate family as Austrobaileyacae and Paeoniaceae respectively.

Role of Palynology in Taxonomic evidence:-

> Palynology is the science, which deals with Pollen grains. The term is derived from Greek verb Palynein means to scatter. Pollen grains are often easily disseminated by wind etc., Pollen grains are found in every nook and corner, e.g., in glacier ice, in the air over the poles and over the oceans.

> Fossil spores are found in peat and other sediments, in lignite, coal and shales. They are evident since Pre-Cambrian times hundreds of millions of years ago.

> Pollen grains morphology plays an important role in classification. Pollen grains may be vesiculate (with air sacs); saccate or non saccate, fenestrate or non-fenestrate, colpate (furrows or colpi present) or porate (apertures present at the poles).

> According to position of apertures six subdivisions are made e.g., ceta (down, inwards in a tetrad), ann (up; outwards in a tetrad), zone is the zonal position i.e., at the equator, and panto is uniform distribution all over the spore surface.

> Basic evidentiary characters: Pollen unit type, Pollen grain polarity, Pollen grain shape, Pollen grain symmetry, Pollen grains nuclear state, Pollen wall architecture, Exine stratification, Exine structure, Exine sculpture, Aperture type, Aperture number, Aperture position, Aperture shape and Aperture structure.

> In Magnoliidae the pollen is binucleate. In Caryophyllidae the pollen is trinucleate. In Ericaceae the pollen is in tetrads. In Asclepiadaceae pollen remain in Pollinia. In Taraxaccurn the pollen wall is echinate. In Quercus the pollen wall is scabrate.

Role of Embryology in Taxonomic evidence:-

> Embryology is the study of the successive stages of sporognesis, gametogenesis and the growth and development of embryo.

> Basic evidences are from: Anther loculi number, arrangement, Anther wall formation and endothecium type, Archesporial cell number, Aril presence, Embryo sac development type, Embryo and Embryogeny type, Endosperm type, Integument number and structural type, Ovule orientation type and position, Tapetal type, Perisperm presence, Nucellus character and Haustorium formation type.

> Embryological evidences are important at higher category level e.g., in conjunction with other types of evidences in confirming the systematic position of taxa.

> In Asteridae the ovules are unitegmic and tenuinucellate, in Caryophyllidae the ovules are bitegmic and crassinucellate. The embryo is embedded in Cyperales.

> In Cyperaceae only one microspore per microspore mother cell is formed. Only one of the four microspore develops into pollen grain while other 3 degenerate as in case of normal magaspore mother cell. In Graminales, the embryo is peripheral to endosperm.

> In Onagraceae the embryosac is 4 nucleate Oenothera type as compared to normal 8 nucleus Polygonum type. In such embryosacs, the endosperm is also diploid.

Role of Cytology in Taxonomic evidence:-

> Cytology is the study of the morphology and physiology of cells. Normally anatomists deal with shapes, size, wall structure, pattern, etc. but cytologists deal with the internal organelles of the cell and detailed structure of cell wall.

> Some evidential characters are: Chromosome number, structure and type, Chromosome meiotic behaviour, Ploidy level and type and Chromosome aberration etc.

> Cytological evidences is used for distinguishing taxa; to determine the origin of groups and to understand the evolutionary history of related taxa particularly those at the infraspecific and specific levels cytotaxonomy is a part of experimental taxonomy.

> Such studies are helpful in determining the categories of genus, species etc. generally in cases of controversy. The study of homologies of the chromosome in the hybrids as determined in meiosis, is significant indicator in knowing the degree of genetic relationship.

> Hutchinson separated Pandanus, Typha and Sporgonium on the basis of chromosome morphology and kept them under two different orders Pandanales and Typhales. Darlington and Janki Animal (1945), Darlington and Wylie (1955), Love (1977) etc., worked a lot on the chromosome number of various plants. International Association of Plant Taxonomy (IAPT) published on Index to Plant chromosome number in series of Ragnum vegetabile (1967- 77) in 9 volumes. Diploid numbers are indicated as 2n and haploid as n.

> The gametophytic chromosome number of diploid species is designated as base number (x). In diploids n = x, in polyploids n is multiple of x. e.g., in hexaploid sp 2n = 6x and n = 3x as 2n = 24 and n = 21.

> Angiosperm, the chromosome number varies greatly e.g., n = 2 in Haplopappus gracilis (Asteraceae) and highest is n = 132 in Poa litloroa (Poaceae).

Role of Phytochemistry in Taxonomic evidence:-

> Chemo Taxonomy:- The science of chemical taxonomy is based on classification of Plants on the basis of their chemical constituents related with the molecular characteristics.

> Chemotaxonomy includes: 

(i) Investigation of pattern of the compounds existing in plants,

(ii) Investigation pattern of the compounds in plant parts likes bark, wood, eaves, roots etc.

> Basic characters as evidence come from: Flavonoids, Terpenoids, Carotenoids, Polysaccharides, Alkaloids, Aminoacids, Fattyacids, Aromatic compounds and C3-C4 photosynthesis etc.

> Development of plant natural product chemistry revealed possibility of characterizing classifying, and establishing phyletic relationships of genera, in (1699) it was first indicated correlating between chemical properties and morphologically character i.e., morphologically similar plants possess similar chemicals.

> Popularity of Phytochemistry is due to:

(a) Development of rapid analytical techniques.

(b) Belief that data from many sources should be employed for classification.

> Mentzar (1966) provided biogenetic classification on the basis of natural relationships between various constituents.

> Micromolecules:-

i. Primary metabolites (Organic acid, Amino acid, Sugar, Chlorophyll) present in each plant

ii. Secondary metabolites (Alkaloids, Terpenoids, phenols, Specific Glucosids etc.,) present in plants.

> Macromolecules:- Chemicals for various functions Semantides (DNA, RNA, Protein etc.) Non- semantides (Starch, cellulose etc.)

> Primary metabolites:- 

i. These are compounds present in vital metabolic pathways.

ii. They are universal in distribution.

iii. They are of little taxonomic value.

> Among the Amino acids the distribution of single amino acids restricted e.g., Lathyrus martinus has protein which is absent in other species of Lathyrus.

> Lipids:- Members of Asteraceae lack unsaturated lipids. Lipids are heterogenous group present in storage organs. It depletes in dark.

i. Linolenic rich seeds e.g., Rhamnaceae.

ii. Linoleic rich seeds e.g., Juglans, Liliac etc. Oleic and Palmitic rich e.g., Acanthaceae, Annonaceae, Malvaceae etc.

> Pigments:- 

- Chlorophyll and carotenoids are fat soluble Biloproteins and Anthocyanins are soluble in water. Anthocyanins and Betalins never coexist. Betalins are low molecular weight substances. Betacyanin gives purple colour and Betaxanthin gives yellow colour.

- Phytochemistry can supply data of use to the taxonomists. It is mainly based on the supposition that related plants will have a similar chemistry e.g., in Pinus every species has different type of terpentine. In Lichen chemical methods are largely used for the identification of genera an species.

- The approach in chemotaxonomy these days in the systematic surveying of plant groups for the three large classes of substances:

i. The primary of basis substances e.g., Nucleic acids, proteins, chlorophyll and polysaccharides.

ii. The secondary constituents of low molecular weight, which are bi- products of major metabolic pathways.

iii. Miscellaneous substances: Secondary product play a major role in biochemical septemates. These are alkaloid, non protein amino acids, flavonoids, glycosides, terpenoids etc.