Botany - B.Ye. Yakubenko 2017

Part Three. The Plant Kingdom (Plantae)
Chapter VII. Systematics of Higher Plants
7.1. General characteristics of higher plants, their origin and classification

Higher plants are predominantly terrestrial plants whose bodies are differentiated into vegetative Organs. A small group of them have a thallus-like body.

A key feature of higher plants is the high degree of Tissue and organ differentiation associated with their terrestrial lifestyle. Their reproductive organs are multicellular.

Higher plants inherited oogamy and a biphasic life cycle from their ancestors, characterized by the alternation of two interdependent phases, or generations: the gametophyte, which produces sexual organs with Gametes, and the sporophyte, which forms sporangia with spores. Only the sporophyte develops from the zygote, whereas the gametophyte develops from the spore. Higher plants have diverged into two evolutionary pathways: in The life cycle of some plants, the gametophyte is dominant, while in others, the sporophyte prevails. Thus, the Main characteristics of higher plants are:

- Differentiation of the body into Tissues and organs;

- The Emergence of an advanced Vascular System;

- the appearance of cambium;

- the advent of heterospory;

- multicellular reproductive organs — sporangia and gametangia;

- independence of the Fertilization process from Water in most representatives.

Higher plants are descendants of lower aquatic plants. Through evolution, certain green and brown Algae achieved a high level of development and significant thallus Cell Differentiation, which paved the way for their transition from water to land. According to Academician A. Takhtajan, the phylogenetic links between Higher Plants and algae are supported by the following facts:

1. In Earth's history, the age of algae preceded the age of higher plants; through long aquatic evolution, algae attained vast diversity in Structure AND TYPES of reproduction.

2. Various groups of algae developed the alternation of two generations in their life cycle — sporophytes and gametophytes.

3. Fertilization in most higher plants, particularly lower vascular plants, requires a liquid water medium, which indirectly proves that the ancestors of higher plants were aquatic lower plants.

4. The most primitive higher plants—rhyniophytes and bryophytes—exhibit dichotomous branching, characteristic of the thalli of highly organized algae.

5. There are similarities in the Structure and function of METABOLISM/14.html">Chloroplasts as well as their pigment composition.

Modern higher plants are divided into the following divisions: Bryophyta, Rhyniophyta, Psilotophyta, Lycopodiophyta, Equisetophyta, Pteridophyta, Pinophyta (Gymnosperms), and Magnoliophyta (Angiosperms).