What are the basic characteristics of algae plants? What is the classification basis of algae?

The concept of algae is different from ancient times to modern times. China ancient book said: "gnats, aquatic plants, or algae." It can be seen that the algae in ancient China are the floorboard of aquatic plants. In modern botany in China, the word "algae" is still used in the names of some aquatic higher plants (such as Ceratophyllum, Kuroshio, Sargassum and Myriophyllum). ), may also come from this. On the contrary, people often call some small sticky green plants in water or on wet ground and walls moss. In fact, this is not moss now, but mainly algae. According to the modern understanding of algae plants, algae are not a natural taxonomic group, but they have the following characteristics:

1. Plants generally have no real differentiation of roots, stems and leaves. The morphological structure of algae plants is very inconsistent, and the size is also very different. For example, Chlorella, which is well known, is spherical and consists of single cells with a diameter of only a few microns; Macrocystis growing in the ocean has a complex structure, and its body length can reach more than 200 meters. Although the individual structure of algae plants varies in complexity and size, there is no real difference between roots, stems and leaves. Some macroalgae, such as marine kelp (kelp) and freshwater charophyta, can be divided into roots, stems and leaves in appearance, but there is no vascular bundle system in the body, so they are not real roots, stems and leaves. Therefore, algae plants are often referred to as phyllodes or protophytes.

2. Inorganic nutrition that can produce light energy Generally speaking, the cells of algae contain the same photosynthetic pigments as green higher plants, and some groups also have special pigments, and most of them are not green, so their plastids are called chromophores or chromophores. Algae can be nourished in various ways. For example, some lower unicellular algae can also be nourished by organic light energy, inorganic energy or organic energy under certain conditions. But most algae, like higher plants, can use carbon dioxide and water to synthesize organic matter under light conditions for inorganic photonutrition.

3. The reproductive organs are mostly composed of single cells. Sporangium that produces spores or sperm and egg storage devices that produce gametes in higher plants are generally composed of multiple cells. For example, mosses and ferns have a sterile cell wall outside the archegonium that produces eggs and sperm that produces sperm. But in algae, except for a few species, their reproductive organs are all composed of single cells.

4. The fertilized egg will not develop into an embryo in the mother. The zygote (fertilized egg) formed by the fusion of male and female gametes in higher plants develops into a multicellular embryo in the mother, and then continues to develop into a new individual without the mother. However, the fertilized eggs of algae do not develop into embryos in the mother, and only after leaving the mother can they divide and grow into new individuals. In zoology, higher plants are viviparous while algae are oviparous.

In a word, algae plants are a large class of representative algae that live a photoautotrophic life without real root, stem and leaf differentiation, and their reproductive organs are composed of single cells without embryos.