BOTANY WITH BASICS OF HYDROBOTANY - 2010

5. PLANT SYSTEMATICS

Systematics is a branch of botany focused on the Classification of plants in relation to their evolution. Its primary objective is to describe and identify all extant and fossil plants, as well as to categorize them into taxa (units) of a specific rank. Consequently, systematics is divided into floristic and phylogenetic branches. Floristic systematics aims to describe all plant species on Earth—essentially compiling an inventory—whereas phylogenetic systematics seeks to construct a plant Taxonomy that reflects the historical Development of Plants and the Phylogenetic relationships among them across all levels.

The Significance of systematics is profound, as advancing the scientific foundations of genetics, breeding, and nature conservation is impossible without understanding the phylogenetic relationships of the families to which the studied species belong.

There are approximately 500,000 plant species on Earth. The entire plant kingdom is divided into two major groups: lower plants and higher (or leafy) plants.

Lower plants comprise unicellular and Multicellular Organisms whose vegetative body (thallus) lacks true Organs (roots, stems, leaves). Their reproductive organs are predominantly unicellular. This group includes prokaryotic and eukaryotic Algae, as well as slime Molds, Fungi, and Lichens.

Higher plants encompass those whose bodies are overwhelmingly differentiated into roots, stems, and leaves, possessing true Tissues and a stele, alongside multicellular reproductive organs. These include bryophytes, rhyniophytes, psilophytes, lycophytes, horsetails, ferns, gymnosperms, and angiosperms (flowering plants). All higher plants except flowering ones possess a female reproductive organ known as an archegonium, which is why they are also referred to as archegoniates.

5.1. Plant Nomenclature. In plant classification, taxa (systematic units) are arranged in a specific hierarchical order. The principal taxonomic ranks include: division, Class, order, family, genus, and species. Each of these taxa may be subdivided into intermediate units: subdivisions, subclasses, subfamilies, and so forth. Some taxonomists also distinguish infraspecific units within a species, such as subspecies, varieties, and forms. The highest systematic unit is the division, while the primary (fundamental) unit is the species. Since the time of C. Linnaeus, binomial nomenclature has been used to designate species,

according to which each species is named using two words—a noun and an adjective—where the first indicates the genus, and the combination designates the species as a whole, for example, Potamogeton lucens, Nymphaea alba, Lemna minor. This nomenclature has become universally adopted through The Use of Latin.

Species. The first biological definition of a species was introduced by the English naturalist J. Ray in 1686. According to Ray, a species is a collection of plant offspring originating from the seeds of a single plant; thus, he equated The concepts of "species" and "variety".

The Swedish scientist C. Linnaeus interpreted the species as the fundamental form of existence in living nature, representing its real and elementary unit. For Linnaeus, a species is "a group of plants that are very similar in their hereditary and morphological traits and distinctly differ from other plants." While Linnaeus introduced METABOLISM/2.html">THE CONCEPT OF the reality and universality of species, his framework was flawed by the dogma of species fixity. He viewed the constancy of a species through continuous reproduction across generations and its dispersal into new environments as absolute immutability.

At the end of the 18th and the beginning of the 19th centuries, the precursors of early evolutionism emerged, championed by the French scientist J.B. Lamarck. However, while convinced that species evolve and change, Lamarck failed to reconcile the idea of species evolution with the undeniable reality of species in nature. Consequently, in the quest to understand the species as a historical phenomenon, an alternative arose: either a "real immutable species" or "evolution without species."

A comprehensive Treatment of the species was provided by C. Darwin in On THE ORIGIN OF Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (1859). The application of the historical method made it possible to synthesize the concepts of species reality and evolution. Darwin demonstrated the reality of species against the backdrop of their evolution, establishing the species as a historical phenomenon. A species arises, reaches its peak development, declines due to changing environmental conditions and The Emergence of competitors in the struggle for life, and ultimately becomes extinct.

A major contribution to The Study of THE SPECIES CONCEPT was made by K. Timiryazev, who emphasized that a species is not only a formal-logical concept but a natural-historical one; alongside S. Korzhinsky, I. Pachosky, V. Komarov, N. Vavilov, and K. Zavadsky.

In his work The Doctrine of the Species in Plants (1940), V. Komarov synthesized all prevailing views on the species problem at the time and formulated it as follows: "a species is a collection of generations descending from a common ancestor, which, under the Influence of the environment and the Struggle for Existence, has been segregated by selection from the rest of the living world; at the same time, a species represents a specific stage in the evolutionary process."

Following detailed and prolonged research on cultivated plants, N. Vavilov concluded that a species is "a discrete, complex, dynamic morphophysiological system linked in its genesis to a specific environment and distribution area (geographical range)." With this, Vavilov disproved the notion of the indivisibility of the species and proved its polymorphic nature.

Overall, the DOCTRINE OF THE species remains one of the most complex fields in biology, and a universally accepted definition of a species does not yet exist. However, a broadly acceptable definition is as follows: a species is a group of populations of individuals capable of interbreeding to produce fertile offspring, occupying a specific geographical range, sharing common morphological and physiological traits and types of interactions with the abiotic and biotic environment, and isolated from other such groups of individuals by the near-complete absence of transitional forms.

5.2. Forms of Life on Earth. There are approximately 5 billion different organisms in the biosphere. The majority of them possess a cellular Structure. However, there are living entities consisting solely of a nucleic acid molecule (DNA or RNA) enclosed in a protein coat—Viruses. They represent the simplest form of life: the acellular form.

In most living organisms, the body is composed of a single Cell (unicellular) or many Cells (multicellular). Based on Structural Features of their cells, cellular organisms are divided into two groups: PROKARYOTES AND EUKARYOTES. A third form has also been discovered—mesokaryotes—which are organisms with an intermediate type of genetic apparatus Organization.

Prokaryote (from Latin pro — before, prior to, and Greek karyon — kernel, Nucleus) means pre-nuclear. Such living organisms lack a well-defined nucleus, and their genetic material is located directly within The Cell protoplasm as a DNA molecule, unprotected by a nuclear membrane. Prokaryotes include Bacteria and blue-green algae.

Eukaryote, translated from Greek, means possessing a true nucleus. Eukaryotic cells contain a distinct nucleus separated from the Cytoplasm by a double membrane. Eukaryotes include all animals and higher plants, unicellular and multicellular algae, and fungi.