CHARA – STRUCTURE & REPRODUCTION notes By Rohit Jirobe

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 CHARA – STRUCTURE & REPRODUCTION

Systematic Position

  • Division: Chlorophyta

  • Class: Chlorophyceae

  • Order: Charales

  • Family: Characeae

  • Common Name: Stone-worts / Brittle-worts

Habit & Habitat

  • Freshwater, submerged algae commonly found in ponds, lakes, tanks and slow-moving waters.

  • Prefer clear and calcium-rich water.

  • Thallus often gets encrusted with CaCO₃, making it hard and brittle → “stone-wort.”

External Morphology (Thallus Structure)

  • Plant body is macroscopic, green, branched and attached to substratum by multicellular rhizoids.

  • Thallus is clearly differentiated into:

    • Nodes (short regions),

    • Internodes (long, single cells).

Internodal Cell

  • Each internode is a single huge cylindrical cell, sometimes several centimeters long.

  • Many species show cortication where small cortical cells form a layer around the internodal cell.

Nodes

From each node arise:

  1. Branches of limited growth (appear like leaves).

  2. Stipulodes – small, leaf-like protective structures.

  3. Branches of unlimited growth (secondary branches).

  4. Sometimes reproductive structures (globule and nucule) develop on the upper nodes.

Cell Structure

  • Cell wall: cellulose + pectin + CaCO₃ deposits.

  • Cytoplasm is peripheral with many chloroplasts (generally without pyrenoids).

  • Central vacuole large; nucleus present in nodal cells.

 

Vegetative Reproduction

Chara multiplies vegetatively by various specialized structures:

1. Amylum Stars

  • Star-shaped structures formed on lower nodes.

  • Rich in starch; detach and form new plants.

2. Bulbils

  • Small, swollen, starch-filled bodies found on rhizoids or lower nodes.

  • Help in perennation and propagation.

3. Tubers

  • Formed on subterranean nodes.

  • Thick and nutrient-rich; survive unfavourable seasons.

4. Secondary Protonema

  • Any vegetative cell may produce a protonema-like filament.

  • This develops into a new thallus.

Sexual Reproduction (Oogamous)

  • Chara shows highly advanced oogamous reproduction.

  • Sex organs are complex and appear on the upper nodes of branches of limited growth.

  • Many species are monoecious (both sexes on same plant); some are dioecious.

Male Sex Organ: Globule (Antheridium)

Structure

  • Appears as a small, spherical, orange or red structure.

  • Borne at the node just below the nucule.

  • Globule is enclosed by 8 large shield cells arranged like plates forming a sphere.

Internal Organization

  • Each shield cell gives rise to a long manubrial cell.

  • Manubrial cell leads to a capitular cell.

  • From each capitular cell arise many spermatogenous filaments.

  • Each cell of these filaments forms a spirally twisted, biflagellate sperm.

Important Point

  • Sperm are highly motile and swim towards the nucule.

Female Sex Organ: Nucule (Oogonium)

Structure

  • Located just above the globule.

  • Appears as an oval, green structure.

  • Surrounded by five long tube cells that twist spirally around it.

  • Tube cells end in five crown cells, forming the corona.

Inside the Nucule

  • A single large egg is present.

  • The lower part forms the venter, upper part forms the corona.

Maturation

  • During maturity, the upper ends of the spirally twisted tube-cells separate, forming a small opening to allow sperm entry.

Fertilization

  • Numerous sperms are released from the globule.

  • They swim towards the nucule.

  • One sperm enters through the gap formed by tube cells and fuses with the egg.

  • Sperm + Egg → Oospore (Zygote).

  • Oospore develops a thick, ornamented wall for protection.


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