Algae Reproduction Overview

Algae uses different types of reproduction methods such as;

1. Vegetative Methods
   1. Budding
   2. Cell Division
   3. Fragmentation
   4. Bulbils
   5. Hormogones
   6. Amylum Stars
2. Asexual Reproduction or Reproduction by Spores
   1. Akinetes
   2. Autospores
   3. Aplanospores
   4. Bispores
   5. Carpospores
   6. Endospores
   7. Exospores
   8. Hypnospores
   9. Monospores
   10. Neutral Spores
   11. Paraspores
   12. Statopsores
   13. Tetraspores
   14. Zoospores
3. Sexual Reproduction
   1. Isogamy
   2. Anisogamy
   3. Oogamy
   4. Autogamy

Different Modes of Algae Reproduction

1. Vegetative Methods

• In vegetative reproduction, the thallus gets separated from the parent and develop a new daughter cell.
• The newly formed daughter cell is genetically identical to parent and no variation is observed.

The vegetative reproduction is accomplished by different methods such as;

(i). Budding

In this method, the vesicles are started to enlarged and then detach from the parent body and form a new thallus.

Example: Protosiphon

(ii). Cell Division or Fission

In this method, the parent unicellular algae mitotically divides into two daughter cells by Fission or septum formation.

Example: Chlamydomonas, Diatoms.

(iii). Fragmentation

This is considered as the most common method of algal reproduction. In this method, the filamentous thalli breaks into two or many fragments. Then each fragment of thalli grows and formed a new filament.

The fragmentation or breakdown of fragment can be occurred by mechanical pressure, insect bite etc.

Example: Ulothrix, Spirogyra, Oedogoniwn, Zygnema, Oscillatoria etc.

(iv). Bulbils or Tubers

Some algae reproduce by the formations of bulbils. Bulbils are the tuber-like outgrowth which are spherical or globular shape, developed at the rhizoidal tips. They formed due to the storage of food.

These Bulbils or Tuber like structures develop a new plant or thallus after getting separated from the parent plant

Example: Chara.

(v). Hormogonia

Hormogonia are the small fragments of varying length. They formed by the fragmentation of the main filament. They can be developed at the place of heterocyst in the filaments.

Example: Occurs in blue-green algae like Nostoc, Cylindrospermum

(vi). Amylum Stars

It occurs at the lower nodes in Chara. These are star-shaped aggregation of starch.

(vii). Adventitious branches

These are the outer growth or new growing tissue from the thallus in algae. These are produced as a means of tissue repair and regeneration.

2. Asexual Reproduction or Reproduction by Spores

• Asexual Reproduction is accomplished with the help of different spores and structures.
• It lacks the fertilization and fusion of nuclei.

There are present different methods of Asexual Reproduction such as;

(i) Akinetes

• They have a thick wall and with an abundance of food reserves.
• Akinetes endure unfavorable conditions and germinate on the presence of favorable conditions.
• They are no-motile.
• After releasing from the parent cell, they develop new thalli.
• Example: Nostoc, Gloeotrichia, Ulothrix, Cladophora, Pithophora. etc.

(ii) Autospores

• Autospores are developed under unfavorable conditions when the protoplast within the sporangium divides and forms spores. These spores are identical to the parent plant.
• They are thick-walled, non-motile, and abundant in food reserve.
• Example: Chlorella, Scenedesmus, etc.

(iii) Aplanospores

• Aplanospores forms by the repeated division of sporangium of parent plants during unfavorable conditions.
• These are non-motile structures with a thin cell wall which is covering the protoplasm.
• Example: Ulothrix.

(iv). Bispores

• When two different spores are developed within a sporangium they are known as bispores whereas the sporangium is termed as bisporangium.
• Example: Reported in Grateloupia filicina ; Porphyra and in Lithophylum littorale .

(v). Carpospores

• During the triphasic life cycle of Rhodophyceae members, Carpospores are formed within the carposporangium.
• Carpospores are diploid in nature but developed from the zygote.
• Example: Polysiphonia , Gracilaria , and Grateloupia

(vi). Endospores

• Endospores are developed within the sporangium by the successive repeated divisions of cell contents.
• After the formation of endospores, the sporangium opens and liberate the motile spores from it.
• Example: Dermocarpa clavata.

(vii). Exospores

• During exospore formation in Cyanophycean members, the sporangium gets burst at the apex and is exposed to the external environment and further by successive repeated divisions of cell contents the spherical spores are formed which are termed exospores. All spores get liberated one by one. 
• Example Chamaesiphon, Stichosiphon.

(viii). Hypnospores

• Hypnospores is a type of Aplanospores which has thick-walled and abundance of food reserve.
• They formed zoospores by the germination or by the division of protoplast. After that those zoospores are germinated to a new plant.
• Example: Pediastrum, Sphaerella etc.

(ix). Monospores

• Monospores define as when Single spores are formed within a sporangium.
• They are mostly found in Brown and red algae.

(x). Neutral Spores

• Neutral Spores are formed when the vegetative cells directly gets transformed into spores. 
• Example: Found in red algae such as Bangia.

(xi). Paraspores

• Paraspores are formed when more than four spores are developed due to the reduction division in a sporangium in red algae.
• Paraspores also known as the polyspores.
• Example: Palmaria elegans , Ceramium sp.

(xii). Statopsores

• Thick and ornamented smooth-walled spores of Bacillariophyceae are refered as the  Statopsores.
• Example: Chaetoceros (Bacillariophyceae), Chrysophyceae, Xanthophyceae etc

(xiii). Tetraspores

• These are mainly found in red algae and are formed in four in number in a tetrasporangium
• Example: Porphyra , Gracilaria , Grateloupia, etc.

(xiv). Zoospores

• These are motile and naked.
• Zoospores can be haploid or diploid and are formed within zoosporangium.
• The zoospores of Vaucheria are known as synzoospores as they are multinucleate and multifagellate.
• They may contain two or four or many flagella.
• Example: Biflagellate zoospores: Chlamydomonas , Ulothrix; Quadriflagellate: Ulothrix; Multiflagellate: Oedogonium.

3. Sexual Reproduction

The sexual reproduction can found in all members of algae except Cyanophyceae. In this method, two opposite gametes fuse and form a new zygote.

Sexual reproduction is classified into different groups based on the structure and fusing behavior of gametes;

(i). Isogamy (iso – similar)

• In this method two morphologically and physiologically similar gametes are fused and formed new zygote.
• Example: Chlamydomonas , Ulothrix etc.

(ii). Anisogamy (aniso – dissimilar)

• In this method, two morphologically and physiologically different gametes are fused and formed a new zygote.
• Example: Chlamydomonas, braunii etc.

(iii). Oogamy

• In this method, a smaller motile male gamete and a larger non-motile female gamete fused and formed a new zygote.
• This sexual reproduction method is also found in some higher plants and animals too.
• Example: Chlamydomonas , Oedogonium , Chara , Polysiphonia , Porphyra etc.

(iv). Autogamy

• In this method, two haploid gametes are fused which are formed from the same mother cell and. After fusion they form a diploid zygote with no genetic variation.

Example: It is commonly reported in Diatoms.

Further Reading

• Characters of Algae | General Characters of Algae
• Thallus Organisation in Algae
• What is Algae? Characteristics and Occurrence of Algae.

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