Fundamentals of Evolution - Korzh O.P. - 2006

Part III. PATHS OF LIFE DEVELOPMENT

Chapter 19. Main Trends in the Evolution of Living Organisms

19.1. Key Stages in Plant Evolution

The vast majority of plant species are photosynthetic autotrophs that play a vital role in the biogeochemical cycling of matter by replenishing organic reserves and enriching Earth's atmosphere with molecular oxygen. Most plants are characterized by a sessile (substrate-attached) lifestyle, continuous growth throughout life, unique developmental cycles, modular organ formation, and the presence of Plastids within their Cells. Their bodies are differentiated into vegetative and Generative Organs and exhibit significant branching, which increases their relative surface area—an adaptation to specialized Nutrition.

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Fig. 19.1. Evolution of the Structural Organization of the algal body (according to various authors):

1 - amoeboid Structure (Chrysamoeba); 2 - monad (Chlamydomonas); 3 - coccoid (Chlorococcum); 4 - colonial (Endorina); 5 - siphonous (Botridium); 6 - siphonous (Caulerpa); 7 - siphonous (Vaucheria); 8 - heterotrichous (Fischerella); 9 - lamellar (Prasiola)

Flora, as a historically established aggregate of plant species in a given territory, is shaped during the evolution of the plant kingdom in close connection with geological history and the physical-geographical environment. Contemporary flora differs significantly from that of past geological epochs.

The earliest, simplest Representatives of the plant kingdom possessed an amoeboid body shape lacking a rigid Cell wall, a feature still retained by certain modern golden, yellow-green, and dinoflagellate Algae (Fig. 19.1). A crucial milestone in algal evolution was The formation of a cellular support system (Skeleton)—a resilient, continuous polysaccharide cell wall that has been preserved in all subsequent plant lineages.

Because plant nutrients are distributed more or less evenly throughout the environment, these organisms gradually lost their mobility during the course of evolution (such as diatoms and other algae lacking flagella and pseudopodia) and transitioned to a sessile lifestyle. Subsequently, a clear trend emerged toward increasing the surface area of contact between the plant and its environment.

When linear body dimensions increase without cellular differentiation, siphonous organisms are formed (such as Vaucheria, Botridium, etc.), which perish even from minor damage. Therefore, the primary direction of the progressive evolution of the plant world can be considered the transition to Multicellular Organisms capable of functional Cell Differentiation (Fig. 19.1).

The simplest form of plant body is the thallus, which lacks differentiation into distinct Tissues (such as roots, stems, etc.). Filamentous algae acquired a novel feature common to all other plant groups: an indeterminate (open) growth system. They exhibit apical (tip), intercalary (interstitial), and even basal growth patterns. Further differentiation into heterotrichous and lamellar forms (e.g., Laminaria) leads to greater cellular specialization (with the number of cell types increasing up to ten). Nevertheless, the relatively uniform aquatic environment did not allow algae to differentiate their bodies to the point of forming true organs (Fig. 19.1).