Algae belong to lower plants, whose main feature is that they generally have photosynthetic pigments, which can be used for photosynthesis and autotrophic. The reproductive organs are single-celled structures, and the plant structure is simple, including single cells, colonies and multicells, without differentiation of roots, stems and leaves. Most of them live in water.

There are about twenty thousand kinds of algae. Algae can be divided into chlorophyta, Charophyta, Rhodophyta, Phaeophyta and so on according to the different pigments and stored nutrients in cells. The comparison of Chlorophyta, Rhodophyta and Phaeophyta is shown in the following table.

Comparison of Chlorophyta, Rhodophyta and Phaeophyta

name

Photosynthetic pigment species

Stored nutrients

Common plants

chlorophyta

Chlorophylls A and B, α and β carotene, four luteins.

Starch, oil

Chlamydomonas, Volvariella volvacea, Spirogyra, Ulva.

Red algae plant

Chlorophyll A, D, carotene, lutein and phycoerythrin, and some also contain phycocyanin.

Florida starch, fucose.

Porphyra, agar, Gracilaria, sea radish

phaeophyta

Chlorophyll a and c, β carotene, hexaphycoerythrin.

Seaweed starch, mannitol, oil, reducing sugar, iodine.

Laminaria japonica, Undaria pinnatifida, Reticularia japonica, carrageenan.

There are three ways to reproduce algae: vegetative reproduction, asexual reproduction and sexual reproduction.

Algae plants have important natural and economic significance. 90% photosynthesis on the earth is completed by algae plants in the ocean and fresh water. Algae plants not only provide food for aquatic plants, but also are important sources of oxygen in water and atmosphere.

Second, lichens.

Lichen is a perennial lower plant, which is a complex of algae and fungi. Lichens have no differentiation of roots, stems and leaves. Fungal hyphae wrap around algae cells and surround algae from the outside. Most of the organic matter produced by algae photosynthesis is captured by fungi, and algae are isolated from the outside world. The required water, inorganic salts and carbon dioxide are absorbed and supplied by fungi from the outside.

Lichens can be divided into shell, leaf and dendritic according to their growth types. The reproduction modes of lichens mainly include vegetative reproduction and sexual reproduction. Lichen has a strong ability to resist drought, cold and other adverse environments.

There are about 25,000 species of lichens, which are generally divided into three categories: ascomycetes, basidiomycetes and algae. Common litmus, usnea, tremella, Icelandic clothes, plum clothes, etc.