MEDICAL BOTANY - A.G. Serbin - 2003

SECTION 3. SYSTEMATICS

Plant systematics studies The Diversity of the plant kingdom, identifies, describes, and classifies plants, assigns them names, and traces evolutionary pathways and phylogenetic relationships. As a science, it took shape in the 16th century. The primary goal of systematics is to understand plants and establish a unified System of the plant kingdom. In the apt words of Academician A. L. Takhtajan, "systematics is simultaneously both the foundation and the crown of biology, its beginning and end, its Alpha and Omega." Systematics encompasses such closely interrelated fields as Taxonomy, nomenclature, and phylogenetics.

Taxonomy, or Classification, deals with the arrangement of plants into a hierarchically subordinated system of categories based on their Structure, origin, and biological and physiological traits. Taxonomy employs specific ranks and levels of classification known as taxonomic categories or systematic units. The principal ones are: species — species, genus — genus, family — familia, order — ordo, Class — classis, division — divisio or phylum, and kingdom — regnum. Intermediate categories exist between the main ones: subspecies, subgenus, subclass, superkingdom, subkingdom, and others. Specific taxonomic categories comprise definite groups of organisms, termed taxa. Nomenclature is the discipline responsible for naming these groups. For instance, family is a taxonomic category, whereas the family Solanaceae is a taxon. Every taxon at a given level features a standardized suffix in its name (e.g., division — phyta, class — psida, family — aceae, genus — a or — um). This allows one to determine the taxonomic category from the name of the taxon without explicitly stating it. All taxa except species are designated by a single word, while species are designated by two: the first word specifies the genus to which the species belongs, and the second, combined with the first, forms its specific epithet. Binomial nomenclature was proposed by C. Linnaeus, who described and named a vast number of plants. According to this system, the generic name is a noun capitalized, while the specific epithet is an adjective written in lowercase. The specific name is followed by the abbreviated surname of the author who first described and named the plant (e.g., Equisetum arvense L. — field horsetail, Linnaeus).

Phylogenetics establishes the evolutionary affinities of species, studying the historical development of plant organisms, taxonomic groups, and the entire plant kingdom. The history of phylogenetics is intertwined with the development and refinement of plant classification systems. Following utilitarian systems, the first scientific classifications were artificial morphological systems based on one or two arbitrarily chosen characters (C. Linnaeus). These persisted until the 17th century, when natural systems emerged, built upon a comprehensive set of morphological traits without regard to phylogenetic relationships (A. Jussieu). In the late 19th century, evolutionary or phylogenetic systems appeared, taking into account the origin and relationships of plant groups, alongside comparative data from molecular biology, Morphology, anatomy, Embryology, karyology, biochemistry, plant geography, and ecology (A. Engler, A.A. Grossheim, A.L. Takhtajan). Since the early 20th century, chemosystematics has been successfully developing as a field based on the comparative analysis of The chemical composition of plants across various taxonomic groups. Chemosystematic data not only contribute to the refinement of plant classification but also guide the search for additional sources of biologically active compounds, leading to the discovery of new medicinal plants.

CLASSIFICATION OF LIVING organisms

The diagrams presented in Figures 3.1 and 3.2 illustrate Examples of Organism classification based on specific criteria, such as cellular structure, level of Organization, and modes of Nutrition.

Fig. 3.1. Classification of living organisms based on Cell Structure and level of organization

Fig. 3.2. Classification of organisms by mode of nutrition

From the perspective of modern phylogenetic systems, the entire plant kingdom shares a common origin and is subdivided into two superkingdoms: pre-nucleated — Procaryota, and nucleated — Eucaryota. A Summary of the latest classification data for organisms traditionally treated as plants (Barr, 1992; Dudka, 1996) is provided in Table 3.1.

Table 3.1. Classification of plant organisms

In botanical studies, it has become customary to distinguish a non-taxonomic, provisional category among organisms classified as plants, namely the lower, or thalloid, organisms. The body of lower organisms (bacteria, algae, slime Molds, fungi, Lichens) is not differentiated into vegetative Organs, and their reproductive organs are unicellular. All other plant organisms are classified as higher plants. Their evolutionary relationships are illustrated in Figure 3.3.

Fig. 3.3. Evolutionary relationships among divisions of higher plants