Chara (Stone worts)
Class: Chlorophyceae Order: Charales
Family : Characeae
Genus : Chara
Chara is macroscopic, submerged aquatic algae. It grows attached to the soft mud at the bottom of fresh water ponds, lakes and slow flowing streams. Mostly they grow in oxygen clear fresh land and still shallow water which has organic matter, Calcium & less oxygen. A few species like C. bactica grow in salt water containing very small percentage of salt.
The plant of chara is impregnated with calcium carbonate and due to this impregnation the plants are rough and brittle to touch. Hence they are called stonewort or brittle wort. The presence of chara over several years results in deposition of marl (calcareous deposits) on the bottom of the pond. Chara usually possess a disagreeable onion like odour which is caused by the presence of sulphureted compounds.
There are about 113 species of genus chara which are worldwide in distribution. About 27 species have been reported from India like C.nuda, C.zeylanica, C. corollina.
Vegetative Structure: Thallus Structure
The plant body or thallus generally grow to a height of 20 to 30 cm and is always erect. The thallus consists of an long, slender, flexous, erect, branched main axis. This axis is attached to the substratum by means of uniseriate, branched and obliquely septate rhizoids.
The main axis is differentiated into alternating short nodes and long internodes. The thallus apparently resembles Equisetum. Due to equisetoid habit this group was named aquatic horsetails by John Ray in 1660.
The internode consists of a single, elongated, multi nucleate, cylindrical cell. It is several times longer than the broad. The node is short and is made up of a cluster of several, small isodiametric cells. Each cluster has two central cells surrounded by 6-20 peripheral cells. From the peripheral cells of a node arises 4 types of structures. They are 1. Primary laterals or branchlets, 2. Auxillary branches of unlimited growth, 3. Stipulodes and 4. Corticating threads or cortex.
Primary laterals or Branchlets:
each node a whorl of short branches of limited growth arise from the peripheral cells. These are called the branchlets or primary laterals or leaves. The branchlets of successive nodes alternate with each other. Each branchlet arise from the peripheral cell of node which functions as an apical cell.
The branchlets consists of limited number of nodes and internodes (4-20),characteristic of a particular species. The lower most node is designated as the basal or basilar node. The primary laterals in turn develop much shorter, one celled, spine like branches called secondary laterals at their nodes.
Auxillary branches of unlimited growth
From the axils of the primary laterals or branchlets, branches of unlimited growth develop which are similar to the main axis in structure. Being apparently axillary in position, they are often called the axillary branches. The axillary branches also contain nodes, internodes, ‘leaves’, stipulodes and sex organs similar to that of main axis.
Stipulodes:
T hey are unicellular, spine like outgrowths that arise from the two lateral cells, one on either side of the basal node of each branchlet. If both the stipulodes are well developed, the species is called bistipulate. In some species, one of the two stipulodes is absent, such species are called unistipulate, e.g., C. braunii, C.nuda. In unistipulate, the number of stipuloses corresponds to the number of branchlets. They are alternate with the latter.
Stipulodes may be arranged in one or two whorls at each node. When arranged in a single whorl, the species is termed as haplostephanous types. If stipulodes are arranged in two whorls it is called diplostephanous type e.g., C. vulgaris, C. zeylanica.
Stipulodes remain rudimentary in C.nuda and C. wallichii. In C. pashanii the stipulodes are absent.
Cortex:
The long intermodal cell may be covered by a sheath of vertically elongated, narrow, ring of row cells called the cortical cells. It constitute the cortex. Half of the cortical cells ensheathing the internode are developed from the node above and half from the node below.
These cortical cells, surrounding cells, surrounding the internode, may or may not be present. If cortical cells are present, the plant is called corticated, e.g., C. zeylanica. If cortical cells are absent, the plant is called ecorticated, e.g., C. wallichii, C. brauni, C. nuda.
Rhizoids:
The thallus is fixed to the substratum by multicellular, branched rhizoids. The septa between the cells are oblique. The main function of rhizoids is attachment and absorption of salt solutes.
Near the tips of rhizoids, a group of statoliths consisting of vacuoles containing crystallites of Barium Sulphate exist. They may be associated with response of the rhizoids to gravity.
Cell Structure:
The nodal cells are small in size. They possess dense, granular protoplast and a single nucleus. The numerous, small discoid chloroplasts are evenly distributed throughout the cytoplasm. Chloroplasts lacks pyrenoids. The cell wall is made up of cellulose.
The internal nodal cell elongates to the length of the mature internode. The single nucleus in it divides to from several nuclei. Thus, the mature intermodal cell is multinucleate. The central portion of the internodal cell is occupied by a large central vacuole. The cytoplasm is differentiated into two zones; the outer stationary exoplasm and inner rotatory endoplasm.
Several round or oval chloroplasts lie embedded in the outer exoplasm. Pyrenoids are absent. The endoplasm forms a thin sieve around the large vacuole. Several nuclei with distinct nucleoli are uniformly dispersed in the endoplasm.
The endoplasm is in constant state of rotation. It flows upon one side of the vacuole and flows down on the other. The streaming of cytoplasm is due to alternating contraction and expansion of the protein fibrils which remain fixed to the cell wall.
The cell wall of the internodal cell is made up of cellulose. However, they are richly impregnated with silica and calcium carbonate, producing hardness and brittleness.
Growth:
The growth of the main axis and the branches is by means of a single, large, dome shaped apical cell, located at the tip of the axis.
The apical cell, by successive transverse walls, cuts off longitudinal series of cells below. Each segment again divides transversely into two cells an upper biconcave, the nodal initial and a lower binconvex, the internodal initial.
The internodal initial doesn’t divide and elongates forming the internodal cell. The nodal initial divides vertically forming two semicircular cells. The subsequent divisions occur in curved planes, each intersecting the preceding plane of division in such a way that there are two central cells surrounded by 6-20 peripheral cells.
Each peripheral cell divides into an apical initial that gives rise to a primary lateral and a basal nodal cell. Each basal nodal cell further divides into an upper and lower cortical cells. Thus internode is enveloped by corticating cells.
The primary laterals exhibit the same method of growth but intenodes are 5-10 and are short.
Reproduction:
Chara reproduces by vegetative and sexual methods only. Asexual reproduction by spores is completely absent.
Vegetative Reproduction:
Chara propagates vegetatively by (i) Amylum stars, (ii) Bulbils, (iii) Protonemal outgrowths.
Amylum stars:
They are developed on the lower nodes of the main axis. Each amylum star is star-shaped, multicellular body formed due to aggregation of cells. The cells are filled with amylum starch.
After being detached from the parent plant, they grow into a new plant. Ex. C. stelligera.
Bulbils:
These are small, rounded, tuber-like structures which are developed on the rhizoids. Ex. C.aspera. Unilateral stem bulbils are developed on the lower nodes, Ex. C. baltica. The bulbils are perennating bodies. After being detached from the parent plant, they give rise to new plant.
Amorphous bulbils:
These are clumps of several small cells laden with food materials. They are produced on the lower stem nodes (C. delicatula) or nodes of rhizoids (C. fragifera) as later outgrowt
They get separated and grow into a new plant.
Secondary protonema:
The naked, adventitious, filamentous, protonema-like branches arises from the surviving nodes of the older plants after hibernation. They may also develop from primary rhizoid ring or dormant apices.
These develop into new plants in the way similar to primary protonema.
Sexual Reproduction
Chara shows highly advanced type of oogamy. The sex organs shows a high degree of specialization and bear a superficial resemblance to the multicellular sex organs of Archegoniates.
They are visible to the naked eye. The male sex organs are called as antheridium or globule and female sex organs are called as oogonia or nucule. Most of the species are monoecious, but a few such as C. wallichi are dioecious. The monoecious species are protantrous i.e., male reproductive organs matures earlier than the female. In monoecious species, globule and nucule develop in pairs at the nodes of the primary laterals on the adaxial side. The oogonium always lie above the antheridium at the same node.
Globule
It is a large, hollow, spherical, bright yellow or red structure. It is attached to the node with an conspicuous pedicle.
The wall of antheridium is make up of eight closely fitting, large, triangular plate like cells, known as shield cells. These shield cells are filled with red or yellow pigments giving characteristics colour to the antheridium. Owing to the infoldings of the cell walls of the shield cells, the antheridial wall appears many celled in longitudinal section. In C. zeylanica, only four shield cells and corresponding number of manubria and capitulum cells are present.
If the walls of antheridium consists of four shield cells, it is called quadriscutate and if that of eight cells it’s octoscutate.
From the centre of each shield cells arises a rod-shaped cell, the manubrium. The eight manubria project towards the centre of the antheridial cavity.
Each manubria bears a terminal cell called the primary head cell or primary capitulum cell. Each primary capitulum cell , in its inner side, buds off six cells – the secondary capitulary cells.
Each secondary capitulum cell produces terminally, a pair of long, whip-like, unbranched, many celled threads called the spermatogenous or antheridial filaments.
The antheridial filaments form a dense tangled mass immersed in a fine mucilaginous material which fills the antheridial cavity. Each filament consists of approximately 1-200 cells. Each cell is small, thin walled and discoid. Each cell functions as a spermatozoid mother cell.
The nucleus of the spermatozoid mother cell elongates to form a spirally coiled, biflagellated spermatozoid or sperm.
The mature spermatozoid is elongaged, spirally coiled structure. The anterior region of the sperm is called the head or orstellum. It consists of flagella, basal bodies and a layer of microtubules.
The head is followed by the major middle region constituting the body of the sperm. It is coiled in a compact helix. The body of the spermatozoid ends posteriorly into an opaque tip constituting the tail region.
When antherozoids are mature the shield cells separate from each other and expose the antheridial filaments and the manubrium to which they are attached.
Antherozoids escape through a pore in the antheridial wall. Antherozoids are released in the morning.
Nucule:
The female sex organ of chara is called the nucule. It is large, oval structure attached at the node of a primary laterl just above the antheridium. Nucule is attached to node with the help of a pedicel cell.
The nucule is enveloped by five long cells which are spirally wound in clockwise direction. The cells are called tube cells. They form a protecting sheath containing the oogonium. Each sheath cell terminates in a small erect cell. Together the small cells form a crown of five closely fitting cells capping the mature oogonium. It is called the corona.
The protoplast of the oogonium produces a single large ovum. It accumulates reserve food materials. The apex of the ovum is occupied by a colourless, granular cytoplasm constituting the receptive post.
The presence of sheath around the oogonium in chara distinguishes it from all green algae. Because of sheath some compare it with the archegonium of Bryophytes.
Fertilization:
At the time of fertilization, the tube cells separate slightly from one another to form five narrow slits. Through these slits the antherozoids gain entrance into the sheath. One of the antherozoid penetrate the oogonial wall by gelatinizing it. It penetrates the ovum at the receptive spot and fuses with ovum to form a zygote.
Oospore:
The zygote secretes a cellulosic thick wall and becomes an oospore. The oospore is retained for some time within the oogonium, external to which is the sheath. The sheath hardens to form a nut-like dark or white coloured case around the oogonium. The white colour is due to the deposition of carbonate of lime.
Eventually, the sheath decays and oospore falls to the bottom of the pond. There it undergoes a period of rest which may extend over weeks or months.
Germination of oospore:
Like other oogamous green algae, the zygote is the only diploid phase in the life cycle of Chara. The diploid oospore nucleus undergoes a meiotic division to produce four nuclei. A septum is formed at this quadrinucleate stage and divide the oospore into two unequal haploid cells.
The upper cell is small and uninucleate. The lower or basal cell is large and contains remaining 3 nuclei. It has considerable reserve food materials. The three nuclei lying in the lower cell soon degenerate.
The oospore wall breaks at the apex to expose the upper cell. Subsequently, the upper cell divides longitudinally into a rhizoidal initial and a protonematal initial. The two grow into knob-like structures in opposite direction.
The rhizoidal initial elongates and develops into a colourless, first or primary rhizoid. The protonematal initial forms an erect, green filament, the primary protonema. It is composed of nodes and internodes.
The mature plant arises as a lateral branch from the protonema. The development of Chara plant as a lateral outgrowth from the protonema is an interesting feature and resembles the mosses.
Life Cycle:
The life cycle of Chara is haplontic. The plant is haploid representing the gametophyte stage. Zygote is the diploid stage. It undergoes meiosis and germinates producing the haploid plant.
Family : Characeae
Genus : Chara
Chara is macroscopic, submerged aquatic algae. It grows attached to the soft mud at the bottom of fresh water ponds, lakes and slow flowing streams. Mostly they grow in oxygen clear fresh land and still shallow water which has organic matter, Calcium & less oxygen. A few species like C. bactica grow in salt water containing very small percentage of salt.
The plant of chara is impregnated with calcium carbonate and due to this impregnation the plants are rough and brittle to touch. Hence they are called stonewort or brittle wort. The presence of chara over several years results in deposition of marl (calcareous deposits) on the bottom of the pond. Chara usually possess a disagreeable onion like odour which is caused by the presence of sulphureted compounds.
There are about 113 species of genus chara which are worldwide in distribution. About 27 species have been reported from India like C.nuda, C.zeylanica, C. corollina.
Vegetative Structure: Thallus Structure
The plant body or thallus generally grow to a height of 20 to 30 cm and is always erect. The thallus consists of an long, slender, flexous, erect, branched main axis. This axis is attached to the substratum by means of uniseriate, branched and obliquely septate rhizoids.
The main axis is differentiated into alternating short nodes and long internodes. The thallus apparently resembles Equisetum. Due to equisetoid habit this group was named aquatic horsetails by John Ray in 1660.
The internode consists of a single, elongated, multi nucleate, cylindrical cell. It is several times longer than the broad. The node is short and is made up of a cluster of several, small isodiametric cells. Each cluster has two central cells surrounded by 6-20 peripheral cells. From the peripheral cells of a node arises 4 types of structures. They are 1. Primary laterals or branchlets, 2. Auxillary branches of unlimited growth, 3. Stipulodes and 4. Corticating threads or cortex.
Primary laterals or Branchlets:
each node a whorl of short branches of limited growth arise from the peripheral cells. These are called the branchlets or primary laterals or leaves. The branchlets of successive nodes alternate with each other. Each branchlet arise from the peripheral cell of node which functions as an apical cell.
The branchlets consists of limited number of nodes and internodes (4-20),characteristic of a particular species. The lower most node is designated as the basal or basilar node. The primary laterals in turn develop much shorter, one celled, spine like branches called secondary laterals at their nodes.
Auxillary branches of unlimited growth
From the axils of the primary laterals or branchlets, branches of unlimited growth develop which are similar to the main axis in structure. Being apparently axillary in position, they are often called the axillary branches. The axillary branches also contain nodes, internodes, ‘leaves’, stipulodes and sex organs similar to that of main axis.
Stipulodes:
T hey are unicellular, spine like outgrowths that arise from the two lateral cells, one on either side of the basal node of each branchlet. If both the stipulodes are well developed, the species is called bistipulate. In some species, one of the two stipulodes is absent, such species are called unistipulate, e.g., C. braunii, C.nuda. In unistipulate, the number of stipuloses corresponds to the number of branchlets. They are alternate with the latter.
Stipulodes may be arranged in one or two whorls at each node. When arranged in a single whorl, the species is termed as haplostephanous types. If stipulodes are arranged in two whorls it is called diplostephanous type e.g., C. vulgaris, C. zeylanica.
Stipulodes remain rudimentary in C.nuda and C. wallichii. In C. pashanii the stipulodes are absent.
Cortex:
The long intermodal cell may be covered by a sheath of vertically elongated, narrow, ring of row cells called the cortical cells. It constitute the cortex. Half of the cortical cells ensheathing the internode are developed from the node above and half from the node below.
These cortical cells, surrounding cells, surrounding the internode, may or may not be present. If cortical cells are present, the plant is called corticated, e.g., C. zeylanica. If cortical cells are absent, the plant is called ecorticated, e.g., C. wallichii, C. brauni, C. nuda.
Rhizoids:
The thallus is fixed to the substratum by multicellular, branched rhizoids. The septa between the cells are oblique. The main function of rhizoids is attachment and absorption of salt solutes.
Near the tips of rhizoids, a group of statoliths consisting of vacuoles containing crystallites of Barium Sulphate exist. They may be associated with response of the rhizoids to gravity.
Cell Structure:
The nodal cells are small in size. They possess dense, granular protoplast and a single nucleus. The numerous, small discoid chloroplasts are evenly distributed throughout the cytoplasm. Chloroplasts lacks pyrenoids. The cell wall is made up of cellulose.
The internal nodal cell elongates to the length of the mature internode. The single nucleus in it divides to from several nuclei. Thus, the mature intermodal cell is multinucleate. The central portion of the internodal cell is occupied by a large central vacuole. The cytoplasm is differentiated into two zones; the outer stationary exoplasm and inner rotatory endoplasm.
Several round or oval chloroplasts lie embedded in the outer exoplasm. Pyrenoids are absent. The endoplasm forms a thin sieve around the large vacuole. Several nuclei with distinct nucleoli are uniformly dispersed in the endoplasm.
The endoplasm is in constant state of rotation. It flows upon one side of the vacuole and flows down on the other. The streaming of cytoplasm is due to alternating contraction and expansion of the protein fibrils which remain fixed to the cell wall.
The cell wall of the internodal cell is made up of cellulose. However, they are richly impregnated with silica and calcium carbonate, producing hardness and brittleness.
Growth:
The growth of the main axis and the branches is by means of a single, large, dome shaped apical cell, located at the tip of the axis.
The apical cell, by successive transverse walls, cuts off longitudinal series of cells below. Each segment again divides transversely into two cells an upper biconcave, the nodal initial and a lower binconvex, the internodal initial.
The internodal initial doesn’t divide and elongates forming the internodal cell. The nodal initial divides vertically forming two semicircular cells. The subsequent divisions occur in curved planes, each intersecting the preceding plane of division in such a way that there are two central cells surrounded by 6-20 peripheral cells.
Each peripheral cell divides into an apical initial that gives rise to a primary lateral and a basal nodal cell. Each basal nodal cell further divides into an upper and lower cortical cells. Thus internode is enveloped by corticating cells.
The primary laterals exhibit the same method of growth but intenodes are 5-10 and are short.
Reproduction:
Chara reproduces by vegetative and sexual methods only. Asexual reproduction by spores is completely absent.
Vegetative Reproduction:
Chara propagates vegetatively by (i) Amylum stars, (ii) Bulbils, (iii) Protonemal outgrowths.
Amylum stars:
They are developed on the lower nodes of the main axis. Each amylum star is star-shaped, multicellular body formed due to aggregation of cells. The cells are filled with amylum starch.
After being detached from the parent plant, they grow into a new plant. Ex. C. stelligera.
Bulbils:
These are small, rounded, tuber-like structures which are developed on the rhizoids. Ex. C.aspera. Unilateral stem bulbils are developed on the lower nodes, Ex. C. baltica. The bulbils are perennating bodies. After being detached from the parent plant, they give rise to new plant.
Amorphous bulbils:
These are clumps of several small cells laden with food materials. They are produced on the lower stem nodes (C. delicatula) or nodes of rhizoids (C. fragifera) as later outgrowt
They get separated and grow into a new plant.
Secondary protonema:
The naked, adventitious, filamentous, protonema-like branches arises from the surviving nodes of the older plants after hibernation. They may also develop from primary rhizoid ring or dormant apices.
These develop into new plants in the way similar to primary protonema.
Sexual Reproduction
Chara shows highly advanced type of oogamy. The sex organs shows a high degree of specialization and bear a superficial resemblance to the multicellular sex organs of Archegoniates.
They are visible to the naked eye. The male sex organs are called as antheridium or globule and female sex organs are called as oogonia or nucule. Most of the species are monoecious, but a few such as C. wallichi are dioecious. The monoecious species are protantrous i.e., male reproductive organs matures earlier than the female. In monoecious species, globule and nucule develop in pairs at the nodes of the primary laterals on the adaxial side. The oogonium always lie above the antheridium at the same node.
Globule
It is a large, hollow, spherical, bright yellow or red structure. It is attached to the node with an conspicuous pedicle.
The wall of antheridium is make up of eight closely fitting, large, triangular plate like cells, known as shield cells. These shield cells are filled with red or yellow pigments giving characteristics colour to the antheridium. Owing to the infoldings of the cell walls of the shield cells, the antheridial wall appears many celled in longitudinal section. In C. zeylanica, only four shield cells and corresponding number of manubria and capitulum cells are present.
If the walls of antheridium consists of four shield cells, it is called quadriscutate and if that of eight cells it’s octoscutate.
From the centre of each shield cells arises a rod-shaped cell, the manubrium. The eight manubria project towards the centre of the antheridial cavity.
Each manubria bears a terminal cell called the primary head cell or primary capitulum cell. Each primary capitulum cell , in its inner side, buds off six cells – the secondary capitulary cells.
Each secondary capitulum cell produces terminally, a pair of long, whip-like, unbranched, many celled threads called the spermatogenous or antheridial filaments.
The antheridial filaments form a dense tangled mass immersed in a fine mucilaginous material which fills the antheridial cavity. Each filament consists of approximately 1-200 cells. Each cell is small, thin walled and discoid. Each cell functions as a spermatozoid mother cell.
The nucleus of the spermatozoid mother cell elongates to form a spirally coiled, biflagellated spermatozoid or sperm.
The mature spermatozoid is elongaged, spirally coiled structure. The anterior region of the sperm is called the head or orstellum. It consists of flagella, basal bodies and a layer of microtubules.
The head is followed by the major middle region constituting the body of the sperm. It is coiled in a compact helix. The body of the spermatozoid ends posteriorly into an opaque tip constituting the tail region.
When antherozoids are mature the shield cells separate from each other and expose the antheridial filaments and the manubrium to which they are attached.
Antherozoids escape through a pore in the antheridial wall. Antherozoids are released in the morning.
Nucule:
The female sex organ of chara is called the nucule. It is large, oval structure attached at the node of a primary laterl just above the antheridium. Nucule is attached to node with the help of a pedicel cell.
The nucule is enveloped by five long cells which are spirally wound in clockwise direction. The cells are called tube cells. They form a protecting sheath containing the oogonium. Each sheath cell terminates in a small erect cell. Together the small cells form a crown of five closely fitting cells capping the mature oogonium. It is called the corona.
The protoplast of the oogonium produces a single large ovum. It accumulates reserve food materials. The apex of the ovum is occupied by a colourless, granular cytoplasm constituting the receptive post.
The presence of sheath around the oogonium in chara distinguishes it from all green algae. Because of sheath some compare it with the archegonium of Bryophytes.
Fertilization:
At the time of fertilization, the tube cells separate slightly from one another to form five narrow slits. Through these slits the antherozoids gain entrance into the sheath. One of the antherozoid penetrate the oogonial wall by gelatinizing it. It penetrates the ovum at the receptive spot and fuses with ovum to form a zygote.
Oospore:
The zygote secretes a cellulosic thick wall and becomes an oospore. The oospore is retained for some time within the oogonium, external to which is the sheath. The sheath hardens to form a nut-like dark or white coloured case around the oogonium. The white colour is due to the deposition of carbonate of lime.
Eventually, the sheath decays and oospore falls to the bottom of the pond. There it undergoes a period of rest which may extend over weeks or months.
Germination of oospore:
Like other oogamous green algae, the zygote is the only diploid phase in the life cycle of Chara. The diploid oospore nucleus undergoes a meiotic division to produce four nuclei. A septum is formed at this quadrinucleate stage and divide the oospore into two unequal haploid cells.
The upper cell is small and uninucleate. The lower or basal cell is large and contains remaining 3 nuclei. It has considerable reserve food materials. The three nuclei lying in the lower cell soon degenerate.
The oospore wall breaks at the apex to expose the upper cell. Subsequently, the upper cell divides longitudinally into a rhizoidal initial and a protonematal initial. The two grow into knob-like structures in opposite direction.
The rhizoidal initial elongates and develops into a colourless, first or primary rhizoid. The protonematal initial forms an erect, green filament, the primary protonema. It is composed of nodes and internodes.
The mature plant arises as a lateral branch from the protonema. The development of Chara plant as a lateral outgrowth from the protonema is an interesting feature and resembles the mosses.
Life Cycle:
The life cycle of Chara is haplontic. The plant is haploid representing the gametophyte stage. Zygote is the diploid stage. It undergoes meiosis and germinates producing the haploid plant.
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