CHARA
(STONE-WORT)

CLASSIFICATION OF CHARA (STONE-WORT)​

Sub-division :- Algae

Class :- Chlorophyceae

Order :- Charales

Family :- Characeae

Genus :- Chara

It is aquatic in habitat. It grows in fresh, clear and standing waters on a muddy or a sandy bottom (epipelic community). These form extensive subaquatic growth. Chara is found below the water level, growing to a considerable depth. It can be collected, almost from any standing or stagnant reservoir of water and occurs in fruiting state during early and late winters. Many species become encrusted with calcium carbonate and are rough and brittle. Chara owes its name ‘Stone-worts’ to calcium deposition.

EXTERNAL FEATURES OF THALLUS OF CHARA (STONE-WORT)​​

• Thallus is macrocopic, branched and multicellular. Calcium carbonate is deposited allover.
• It remains attached to the substratum by multicellular rhizoids which bear an erect and branched main axis above. 
• Multicellular rhizoids are branched.
• These are borne by the lower nodes of the main axis. 
• Rhizoids possess oblique septa. The rhizoids are not differentiated into nodes and internodes.
• The cytoplasm of a rhizoidal cell has a nucleus situated towards the upper side of the cell. 
• At the septum of a rhizoidal cell, the ends are protracted in opposite directions to form knotted part. 
• At this place, signifying a node, a plate of four cells or even more is formed which gives rise to rhizoidal branches. This part is known as rhizoidal plate. 
• Main axis is composed of long internodes alternating with small nodes. 
• Long internode is composed of a single cell enveloped by many corticating threads. 
• A node is a group of regularly arranged cells. 
• It bears two types of branches-
  1. lateral branches of limited growth (short laterals)
  2. lateral branches of unlimited growth (long laterals). 
• Laterals of limited growth are borne in whorls around the nodes of the main axis. 
• Each short lateral is divided into nodes and internodes. 
• The internodes of short laterals are small as compared to those of the main axis. 
• Short laterals borne by the nodes of the main axis are also termed as primary laterals of limited growth.
• From the nodes of the short laterals, secondary short laterals are produced which are usually small, unicellular and are variously termed as stipules or leaves. 
• Laterals of unlimited growth are borne by the nodes of the main axis only. These are situated in the axils of short laterals. 
• Long laterals possess the same characteristics as those of the main axis. 
• Long laterals are differentiated into long, corticated and unicellular internodes and small and multicellular nodes.
• Nodes of the long laterals bear short laterals which in their tum give out stipules or leaves at their nodes.

STUDY OF A CELL OF CHARA (STONE-WORT)​​

• In the center is a large central, axial or internodal cell.
• It is surrounded by corticating threads on all sides. 
• Internodal cell shows a typical cell structure. 
• Centre of the cell has a big vacuole surrounded by cytoplasm. 
• In the cytoplasm lies a single nucleus held by thin and delicate cytoplasmic strands. 
• Many discoid chloroplasts without pyrenoids are scattered in the peripheral cytoplasm. 
• The cell has an outermost, thick and firm cell wall.

L.S. OF APEX OF CHARA (STONE WORT)​

• The cell situated at the top is an apical cell. It contributes to the development of the main axis and lateral axes. 
• It cuts off a longitudinal series of cells below. 
• Upper biconcave cell of a series is a nodal cell and lower biconvex one is an internodal cell. 
• Biconcave nodal cell in the lower parts divides to produce a mass of peripheral cells which surrounds centrally located nodal cell.
• Peripheral cells act as initials of the laterals of limited growth. 
• From peripheral cells of node, laterals are produced which show similar arrangement of nodal and internodal cells alternating with one another. 
• Biconvex internodal cell does not divide but in the lower part simply elongates many times.

BULBILS OF CHARA (STONE WORT)​

• Bulbils are present on the knotted part of the rhizoid or the basal nodes of the main axis.
• These remain buried under the soil.
• These are oval, tuber-like outgrowths.
• Bulbils are rich in starch and hence also called amylum stars. 
• These are the organs of vegetative propagation.

SEX ORGANS OF CHARA (STONE WORT)​

• Most of the species are homothallic (monoecious) while a few are heterothallic (dioecious ). 
• The male reproductive organ is called a ‘globule’ while the female reproductive organ a ‘nucule’. 
• Both the sex organs are borne at one point on the nodes of short laterals which bear stipules. 
• The characteristic feature of the genus Chara is the position of nuclei at the node above the globule.

MALE SEX ORGAN OF CHARA (STONE WORT)​

• A globule is a small, spherical and conspicuously red or yellow structure attached to the node by a long stalk cell. 
• Outermost wall of the globule is ornamented, composed of eight, large, curved and platelike cells called shield cells.
• Ornamentation of the shield cell is due to the foldings in the cell wall. 
• Each shield cell is attached to a long handle or a rod-shaped cell-manubrium.
• At the tip of each manubrium are two groups of six cells each. The group directly in contact with the manubrium is primary capitulum while the next is secondary capitulum.
• Each secondary capitulum bears 2-4, long and unbranched antheridial filaments.
• Each antheridial filament is made of 100-230 small cells. 
• Each of these cells is an antheridium and produces a single biflagellate male gamete

FEMALE SEX ORGAN OF CHARA (STONE WORT)​

• Nucule is oval in shape and is situated above the globule at the node.
• It is enveloped by spirally coiled (coiling clockwise) cells-tube cells. 
• At the apex of the nucule is a corona of five small cells arranged in one tier and attached at one point. 
• Oosphere is single celled where a nucleus lies surrounded by the cytoplasm. 
• It is rich in food reserves which are in the form of starch and oil. 
• After fertilization the nucule gets modified into a zygote or oospore.
• The coronal cells at the top of the oospore appear separated. 
• The oospore wall is thick and ornamented. It has a deposition of calcium.

IDENTIFICATION

• Sub-division– Algae
  1. Presence of a simple thallus.
  2. Chlorophyll present
  3. Cell wall made of cellulose.
• Class – Chlorophyceae
  1. Presence of a definite nucleus
  2. Chloroplast present. grass green colour
  3. Presence of starch
  4. Reproductive structure motile and flagella equal in length.
• Order – Charales
  1. Thallus differentiated into nodes and internodes.
  2. characteristic sex organs-globule and nucule.
• Family – Characeae  (Single family)
• Genus – Chara
  1. Presence of corticating filaments around internodes.
  2. Nucule lying above the globule.
  3. Corona of nucule five celled.

REFERENCES :-

• https://en.wikipedia.org/wiki/Chara_(alga)
• https://en.wikipedia.org/wiki/Chara_(alga)#/media/File:CharaFragilis.jpg