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Chlorophyta

Biotaxonomically, it is a class of Chlorophyta

Chlorophyceae Biotaxonomy On Chlorophyta (Chorophyta). In China, the class of green algae is generally divided into 13 orders: Volvacea, Tetrasporophyta, Chlorococcales, Hymenophyceae, Chaetochaea, Ulva lactuca, Schizophyceae, Sheath Algae, Cisetera, Tracheophyta, Tracheophyta, and Choreodendrophyta. Some people think that higher terrestrial plants may have developed from some ancient green algae.

Chinese scientific name: Chlorophyta
Latin name: Chlorophyceae
circles: Flora

door: Chlorophyta
Outline: Chlorophyta
Distribution area: Most species are produced in fresh water, and a few in sea water.

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brief introduction

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Chlorophyceae is a class in the phylum Chlorophyceae in terms of biological taxonomy. Having single cells, colonies, or multicells; Group fixed or amorphous; The multicellular individuals are spherical, branched and unbranched filamentous, flat leaflike, cup-shaped and empty tubular; With few exceptions, most of the vegetative cells of green algae have cell walls. The outer layer of the cell wall is pectin, and the inner layer is fibrous; Coccidium 、 Sheath algae and Chaetotheca The inner layer of the cell wall of the order Pinophyceae is composed of callose; There are about 8600 species in this phylum, which are distributed from the poles to the equator, and from high mountains to plains. Most species are produced in fresh water, and a few in sea water.

Main features

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① photosynthesis Pigment is chlorophyll and Beta carotene And several xanthophyll ；

② The stored food is mainly starch ；

③ In the life history, swimming with two to four equally long flagella attached to the top Cells ；

④ Sexual reproduction Very common, it is homogamy, heterogamy or egg mating. Algae can be divided into single cell, colony, filamentous body, thallus, tubular multinucleate and other types.

distribution

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There are about 8600 species in this phylum, which are distributed from the poles to the equator, and from high mountains to plains. Most species are produced in fresh water, and a few in sea water. Both floating and fixed species are parasitic and cause plant diseases; In addition, there are also aerial species, some of which are symbiotic with green hydra, and a few of which are parasitic or symbiotic with fungi to form lichens.

life history

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Hypsidium

There are 3 types:

① Haploid algal form, only the zygote is doubled in life history, and the zygote undergoes meiosis when it germinates; There are many green algae of this type, such as chlamydomonas ；

② For diploid algae, only gametes are haploid in life history, and meiosis only occurs when gametes are formed; There are few examples of this type, such as Cymbidium 。 There is no generational alternation between the above two types;

③ Double haploid or single diploid algal body type, this type of green alga has alternate generations, that is, in the life history, sexual generation and asexual generation alternate: the plant body of sexual generation, namely gametophyte, produces haploid gametes; Gametes combine to form a double zygote; The zygote develops into an asexual plant, that is Sporophyte , producing spores; Meiosis is carried out in the process of producing spores; The spores develop into gametophytes, and so on. Many green algae belong to this type, such as Ulva lactuca 。

Cellular structure

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Having single cells, colonies, or multicells; Group fixed or amorphous; The multicellular individuals are spherical branch And unbranched filiform, flat leaflike, cup-shaped and empty tubular; With few exceptions, most of the vegetative cells of green algae have cell walls. The outer layer of the cell wall is pectin, and the inner layer is Fibroin ； Chaetoceros Sheath algae and Chaetomium There is chitin in the cell wall of, Pinophyta The innermost layer of cell wall is composed of callose; It usually has one or more nuclei and vacuoles.

There are obvious plasmodesmata in some groups of Volvox; Each vegetative cell has one to several pigment bodies, which have various shapes, such as cup, star, belt, sheet, mesh, granular, etc; The vast majority of vegetative cells contain one or more protein nuclei, while a few do not; Swimming cells have 2, 4 or more equal flagella.

Taxonomic evolution

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Up to now, no consensus has been reached on the classification system. In 1976, Chinese Algologist Rao Qinzhi It is proposed that the department should be divided into 2 classes and 13 orders, namely:

[Chlorophyta] Swimming cells with flagella in life cycle; Sexual reproduction is common, but there is no conjugal reproduction. Including 12 meshes: Volvocales （Volvocales）， Tetraspora （Tetrasporales）， Chlorococcales （Chlorococcales）， Hymenophyceae ， Gelatina （Chaetophorales）， Ulva （Ulvales）， Prasiolales （Prasiolales）， Coleoptidea （Oedogoniales）， Ciliates （Cladophorales）， Angiophyta （Siphonocladales）， Choreoclada (Dasycladales) and Tracheophyta （Siphonales）。

Wall broken Chlorella powder

[Conjugate Algae] (Conjugatophyceae) There are no flagellated swimming cells in the life cycle; Sexual reproduction only involves conjugation. This class has only one order of Zygnematales.

H. In 1985, Bould and M. Wen proposed to divide Chlorophyta into 1 class, 16 orders, namely Chlorophyta （Chlorophyceae）： Volvocales （Volvoca-les）， Tetraspora （Tetrasporales）， Chlorococcales （Chlo-rococcales）， Chlorocystidea （Chlorosarcinales）， Hymenophyceae （Ulotrichales）， Cyclophyceae （Sphaeropleales）， Gelatina （Chaetophorales）， Citrophyta （Trentepohliales）， Coleoptidea （Oedogoniales）， Ulva （Ulvales）， Ciliates （Cladophorales）， Cephalosporales （Acrosiphoniales）， Dipteroidea （Zygnematales）， Pinophyta （Codiales）， Angiophyta (Siphonocladales) and? Choreoclada （Dasyclada-les）。

Little is known about the evolution of Chlorophyta, and the ancestors of green algae are still unknown. Evolutionary trend of Chlorophyta, according to F F. According to Blackman's opinion in 1900, the most primitive species may be the single cell species, and thus three evolutionary routes are divided:

① From colony to multicellular Volvox;

② From tetraspora to filamentous, flat leaf, cup and tube, higher green plants are believed to originate from coleochaetes in this branch;

③ Chlorococcales are a species that lose true vegetative cell division. There are many known green algae fossils, especially Velvet Branch algae The earliest record is of Precambrian.

Biological use

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Chlorella and Haematocaceae are rich in protein for human consumption and animal feed. Green algae are materials for algae physiological and biochemical research and oxygen donors for space navigation. Some can be used to make alginate. Green algae It plays the role of purifying and indicating organisms in water self purification.

Representative plants

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Volvocales

1 order of Chlorophyta of Volvocales. It is a single cell, group or multicellular species. Most of the front ends of the cells that can swim have 1 pair, or 4, rarely 1 or 8 tail whip type flagella of equal length; With few exceptions, there is a layer of cell wall containing cellulose outside the cells; There is a central nucleus in the cell; 1 cup, a few other shapes, and few more than 1 pigment body; 1 eye spot, 2 retractile bubbles at the base of flagellum, rarely more than 2; During cell division, algal plastids composed of microtubules appeared, and at the end of mitosis, equatorial plates perpendicular to the spindle were formed. All cells of a population are often buried in a common rubber blanket, which can be spherical, elliptical, flat, etc. due to different types. This order has more than 60 genera, most of which are universal species. Single cell species are found in fresh water, salt water, sea water, soil, even ice and snow; The population is mostly freshwater species, living in various water bodies, especially rich in organic nutrients.

Asexual reproduction is very common in Volvox: single cell species are formed by multiple cell divisions, producing 2, 4, 8 or more daughter cells, which are released from the mother cell; Pigment bodies, protein nuclei, etc. are also distributed in daughter cells through their own division; Eyespot and retractile vesicle are regenerated in daughter cells; The type of population, part or all of the cells in the mother, continuously division A young parent like population is generated. After the mother body escapes, there is no cell division in this population, and only the size increases to form a new individual. Sexual reproduction has different ways of homogamy, heterogamy and egg mating due to different types; Some species, such as Chlamydomonas, have these three modes at the same time; Other species often only have one or two of them, but in this order, there is an obvious evolutionary trend from homogamy, heterogamy, to egg mating. The zygote undergoes meiosis during germination. In some species, zygotes germinate to form 4 sporozoites.

Many species in this order are common in temporary ponding, and there are often many individuals. Once the water dries up, they adapt in the form of dormant zygotes or chlamydospores to survive the adverse environment. Some species are planktonic; Some species can form blooms.

The classification systems of Volvox are different, but generally they are based on the fact that the individual is single celled, colony or multicellular. Some of them are divided into 4 suborders, and some are divided into 2 suborders. It is generally divided into 6 families: Polyflagellaceae （Polyblepharidaceae）、 Chlamydomonadaceae （Chlamydomonadaceae）、 Chlamydiaceae （Phacotaceae）、 Haematococcaceae （Haematochrococ-caceae）、 Vertebramoronaceae (Spondylomoraceae) and Volvocaceae （Vol-vocaceae）。

Tetracellular Algae

Tetrasporales: one of the phytoorders of algae. This plant belongs to Chlorophyta （Chlorophyta） Chlorophyta (Chlorophyceae) Volvocales (Volvocales) and so on.

Chromococcales

Chromococcales: an order of Cyanophyta. The explants are single cells or colonies. The colony is spherical, flat, cubic, amorphous, or pseudofilamentous; Free floating or adhering to the substrate. The cells of most genera and species did not differentiate at the top and base; Cells are spherical, elliptical, oblong, Columnar , pear shaped, etc; The cell wall is divided into two parts, the inner layer contains cellulose, which is closely attached to the outside of the protoplasm, and the outer layer is pectin, colorless and transparent, or yellow, brown, red and other colors, homogeneous or obvious bedding. The cells in the population are embedded in a common gel coat, thus forming a certain shape or amorphous population (pal mella). The method of reproduction is cell division or population fracture. There are 1, 2 and 3 division planes.

There are 35 genera and 250 species. The vast majority of freshwater products. It is widely distributed and can survive in various habitats; Most aquatic genera and species live in the water, or attach to objects in the water; Subaerial and aerial genera and species, most of which gather into various lumps and adhere to various substrates such as stones, walls, tree trunks Mosses And other large algal plants or their colloid secretions.

There are three departments: Chromococcaceae （Chroococcaceae）、 Lithocystidae (Entophysalidaceae) and Cyanostemidae （Cyanostolonaceae）。

There are many species and wide distribution of Chlorellaceae, and the most common ones are: Chromococcus （Chroococcus）、 Myxococcus （Gloeocapsa）、 Cladosporium （Gloeothece）、 Bunchocystis （Gomphosphaeria）、 Coenococcus（ Coelosphaerium）、 Planschia （Merismopedia）、 Cryptococcus （Aphanocapsa）、 Cryptostega (Aphanothece), etc, Stellaria (Astero capsa) is an endemic genus of China, distributed in Southwest and South China provinces.

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