Chara belongs to the division Charophyta. This division has only one class- Charophyceae. This class has a single order- Charales.
Order Charales has four families. However, all the living genera under this order are under the family Characeae.
Characeae has two subfamilies- Nitelloida and Charoidae. Chara belongs to the subfamily Charoidae.
There are five genera in the subfamily Charoidae- Chara, Protochara, Nitellopsis, Lychnothamnus, and Lamprochamnium.
All members of Charoidae have an oogonium with five coronal cells.
Thus, the systematic position of Chara can be summerized as,
Division: Charophyta
Class: Charophyceae
Order: Charales
Family: Characeae
Subfamily: Charoidae
Genus: Chara
Chara Characteristics
Chara is a submerged aquatic algae growing on soft mud at the bottom. They are also seen on the margins as well as in slow-flowing streams. The plant body of Chara is a thallus.
Thallus
The thallus is long and slender with upright branches, nodes, and internodes.
Nodes of Chara are short and have clusters of small branches arising from it.
There are four types of appendages arising from nodes.
Branchlets
Branchlets are short branches arising from nodes in a whorl.
They are also called primary laterals.
They have limited growth and are arranged on alternate nodes.
These branchlets have nodes and internodes, but in limited numbers.
This number would be specific to each species and varies from 5-15.
From the primary laterals, short, spine-like, single-celled branches called secondary laterals arise.
Long Branches
Long branches are another kind of branch that arises from the central axis’s nodes.
They have unlimited growth and are single.
Mainly arising in auxiliary positions, they are called axillary branches.
It has a similar structure to the main axis and continues with the thallus growth.
Stipulodes
Stipulodes are unicellular growths arising from the base node of branchlets.
There are two stipulodes at each node, arising on both sides.
The stipulates may be in a circle or row, and such Chara species are called bistipulatae.
Those species with only one type of stipulodes are called unistipulatae.
When Chara has a single whorl of stipulates, it is called haplostephanous, and when they are arranged in two whorls, it is diplostephanous.
In some species, the stipulates are rudimentary and in some, it is absent.
Cortex
Cortex refers to the internodal cells in some species of Chara that are covered by vertically elongated cells. Such species are called corticated, and those that lack a cortex are called ecorticated. Ecorticated species will have naked internodal cells.
Rhizoids
Chara is fixed onto the substratum with the help of rhizoids. Rhizoids arise from the nodes at the lower portion of the axis. This portion does not have nodes and internodes.
Anatomy of Chara Thallus
A vertical section of the thallus of Chara shows smaller apical cells with no vacuoles.
They have a central nucleus in a dense and granular cytoplasm.
Numerous discoid chloroplasts are evenly distributed in the cytoplasm.
Pyrenoids are absent in Chara.
Internodal cells have a large central vacuole.
Chloroplasts are arranged longitudinally in the outer region.
Cytoplasm here is stationary and is called exoplasm.
The cytoplasm close to the vacuole is called the endoplasm.
The streaming movement of endoplasm is called cyclosis.
In mature cells, the single nucleus divides multiple times to become a multinucleated cell.
Reproduction in Chara
Vegetative and sexual reproduction are the only two methods of reproduction in Chara. It lacks an asexual mode of reproduction.
Vegetative Reproduction in Chara
There are four ways by which Chara reproduces vegetatively. It produces certain specialized structures on the various parts of the thallus. These structures, when separated from the parent plant, will grow into a new plant. Those structures are,
Amylum Stars
Amylum stars are star-shaped cell aggregations formed on nodes in the lower regions. Their cells contain amylum starch.
Bulbils
Bulbils are rounded, small, tube-like structures arising on the rhizoids of Chara aspera. They can be unilateral stem bulbs as seen in C. baltica. They will grow into a new plant upon detachment from the parent plant.
Amorphous Bulbils
These are clumps of cells, filled with food materials. In C. delicatula, it is produced from the lowest stem nodes and from rhizoids or nodes in C. baltica and C. fragifera, to appear as lateral outgrowths.
Secondary Protonema
Secondary protonema are protonema-like adventitious, naked branches from the nodes of older plants. They appear after hibernation. Some of these can arise from primary rhizoids as well. They produce new plants.
Sexual Reproduction in Chara
Chara exhibits an oogamous type of sexual reproduction. They produce more specialized and complex sex organs when compared to other algae.
The male sex organ of Chara is called a globule, and the female sex organ is a nucule.
Both globule and nucule are visible to the naked eye.
A globule or antheridium is round, large, and red or yellow in color.
Nucule is oval and large with a multicellular envelope.
Most species of Chara are monoecious, but C. wallichii is dioecious.
The sex organs arise at the nodes in pairs and on the side that faces the axis (adaxial side).
Nucule is always located above the globule.
Antheridium of Chara
According to Goebel, the antheridial axis of Chara has 8 secondary laterals. Each of these secondary laterals is differentiated into a shield, a manubrium, and a primary capitulum.
But other views consider the capitulum cells to be the upper node and the manubrium forms the internodes, while the shield cells are at the lower side.
Antheridium is a spherical hollow structure attached to the node using a pedicel.
The wall of antheridium has 8 shield cells with red or yellow pigments.
A manubrium arises from the centre of each shield cell and ends in a primary capitulum or head cell.
Each head cell produces secondary capitula on its inner side.
Thread-like antheridial filaments arise from these secondary capitula.
Each cell of this filament acts as a spermatozoid mother cells that produce spermatozoids or male gametes.
Oogonium of Chara
The oogonium of Chara is large and ovoid.
It has a single egg with a five-cell envelope.
The envelope is flask-shaped.
Each sheath cell forms a crown of cells called a corona, which caps the oogonium.
Fertilization in Chara
At the time of fertilization, a tube-like septa is formed below the corona to form a slit through which sperms enter the oogonium. Only one sperm gains access through the receptive spot. It fuses with the ovum to form the diploid zygote.
Oospore Formation
The newly formed zygote secretes a cellulose membrane around it to form an oospore. The nucleus migrates to the pole and is retained until conditions are favourable. The sheath hardens and becomes dark or white due to deposition of carbonate of lime. After a dormancy period of weeks or months, the oospore germinates to form a new plant.
Life Cycle of Chara
The main plant body of Chara is haploid.
The only diploid stage in the life cycle of Chara is the zygote, which stays in a dormant state until favourable conditions arise.
Chara does not reproduce asexually via spores.
The vegetative reproduction occurs by the formation of amylum stars, secondary protonema, and bulbils.
Chara exhibits, oogamous type of sexual reproduction.
It shows large and specialised sexual organs which appear in pairs.
Antheridia and oogonia appear on fertile nodes of primary laterals.
After fertilization, the zygote undergoes a resting period, the zygote nucleus undergoes meiosis.
Only one of the four daughter nuclei survives, which germinates to form a new plant.
The Chara plant arises in the form of a lateral bud from the haploid protonema.
References
Vashishta, B. R. (2022). Botany for Degree Students. S. Chand Publishing.
Nishiyama, T., Sakayama, H., De Vries, J., Buschmann, H., Saint-Marcoux, D., Ullrich, K. K., Haas, F. B., Vanderstraeten, L., Becker, D., Lang, D., Vosolsobě, S., Rombauts, S., Wilhelmsson, P. K., Janitza, P., Kern, R., Heyl, A., Rümpler, F., Villalobos, L. I. A. C., Clay, J. M., . . . Rensing, S. A. (2018). The Chara Genome: Secondary Complexity and Implications for Plant Terrestrialization. Cell, 174(2), 448-464.e24. https://doi.org/10.1016/j.cell.2018.06.033
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