Vaucheria

According to Fritsch system of classification, Vaucheria is placed in Chlorophyceae.

Fritsch system of classification:

                  Class – Chlorophyceae

                 Order – Siphonales

                 Family – Vaucheriaceae

                 Genus – Vaucheria

According to Smith, Vaucheria is placed under Xanthophyceae.

Smith system of classification:

Class – Xanthophyceae

Order – Heterosiphonales

Family – Vaucheriaceae

Genus –Vaucheria

which is based on such character which are totally show resemblance with Xanthophyceae. These characters are:

• Presence of carotenoids.
• Reserve food is oil and not starch.
• Characteristic chloroplasts and pyrenoids of chlorophyceae are absent.

   Unique characters:

• Coenocytic
• Gongrosira stage
• Siphonaceous

Occurrence

Terrestrial species: V. sessilis, Vaucheria hamata and Vaucheria terrestris.

Aquatic species: Vaucheria thureti, Vaucheria uncinata, Vaucheria sessilis.

Common Indian species:  Vaucheria sessilis, Vaucheria ambhibia etc.

Vaucheria is represented by 54 species out of which 19 species are found in India. Vaucheria is found mostly in fresh water but about six species are marine and some are terrestrial, found in soil.

Vegetative structure

• Plant body is cylindrical, branched, siphonaceous thallus.
• Yellow green filamentous alga.
• Branching is monopodial but seems like dichotomous.
• Thalli are multinucleate lack cross walls structure called Coenocytic.
• Chromatophores contain chlorophyll a, e; carotene and xanthophyll.
• Reserve food material is oil.

Thallus

• The thallus is made of long cylindrical well branched filament.
• The filament is aseptate, coenocytic structure.
• The thallus is attached to substratum by means of branched rhizoids or branched holdfast called the Haptera. 
• The thallus of V. mayyanadensis is differentiated in subterranean branched rhizoidal system and erect aerial system.
• The filaments are rough interwoven and appear as dark green felt like structure.

Life cycle

Reproduction:

It reproduces by vegetative, asexual and sexual methods.

• Vegetative Reproduction:

 It takes place by fragmentation.

• Asexual Reproduction: It is common method in Vaucheria by the formation of zoospore, aplanospores, Akinetes.

Zoospore:

Multi flagellate and multinucleate produced in club shaped sporangium.

• During development of zoosporangium, tip portion of side branch start swelling and become club shaped dense cytoplasm along with large number of nuclei and chromatophores flow into the sweeping followed by the appearance of septum.

Aplanospores:

• Non motile spores produced under unfavourable conditions.
• It develops under unfavourable conditions.
• Short thick walled and gelationous.
• Akinetes are produced in dichotomous branches in rows this stage is called Gongrosira stage. It resembles like gongrosira algae
• When favorable conditions comes it directly forms a new plant.
• Sexual reproduction (oogamous):

Male sex organ: Antheridia hook shaped

Female sex organ: Spherical

Position of Sex Organ

• Sessile type: Sex organ are formed on main filament. Male and female organs are produced on branches close to each other and are sessile.
• Geminata type: Sex organ are formed on special branches these branches are short and bear terminal antheridium and lateral oogonia.

• Antheridia and oogonia are born on special side branches with a terminal antheridium and number of lateral oogonia.
• In V. hamata the reproductive branches bear a median terminal antheridium and a group of oogonia.
• The sex organ are unilateral when they are arranged on one side of the filament or bilateral when they are arranged on both sides of filament.
•  Antheridia and oogonia are born on adjacent branches.

Structure of Antheridium

• The mature antheridia may be cylindrical, tubular, straight, or strongly covered.
• The antheridium is separated from main filament by a septum.
• The antheridia can be sessile arising directly from the main branch.
• The young antheridium is usually green in colour.
• It contains cytoplasm, nuclei and chloroplasts.
• The mature antheridia are yellow and contain many spindle shaped antherozoids.
• The antherozoids are liberated from the tip of antheridium through apical pore shortly before day break.

Structure of Oogonium

• The oogonium  development starts with  accumulation of colorless multinucleate  mass of cytoplasm near the base of antheridial  branch
• This accumulated cytoplasm has been termed as wanderplasm.
• The wanderplasm enters into the outgrowth   bulging of main filament. This outgrowth is called as oogonial initial.
• Large amount of cytoplasm and nuclei enter into oogonia making it a large globular structure called as oogonium.
• As the oogonium matures it gets separated from the main branch by the development of septum at the base.
•  The mature oogonium is uninucleate structure.
• The nucleus of oogonium with protoplasm develops into single egg.

There are three hypothesis regarding the fate of extra nuclei of oogonium of Vaucheria :

• According to Oltmanns (1895), accept a single nucleus which forms a female nucleus, all other nuclei migrate back into the filament. This was supported by Heidinger and Couch.
• According to Davis (1904), the single nucleus forms the egg and all other nuclei degenerate.

• According to Brehens (1890) all nuclei fuse to form a single nucleus.

Fertilization

• The oogonium secretes a gelatinous drop through a pore near the beak.
• A large number of liberated antherozoid stick to the drop.
• Many antherozoid push into the oogonium.
• The antherozoid strike violently fall back and push forward again and fall back. Only one antherozoid enters into oogonium.
• After its entry the membrane develops at the pore to stop the further entry of antherozoids. The male nucleus increases in size and fuses with egg nucleus to make diploid zygote.
• The zygote secretes a thick 3-7 layered wall and is now called oosphere.

Germination of Oospore

• The oospore undergoes a period of rest before germination.
• During favourable season the oogonial wall disintegrates and oospore is liberated. The oospore germinates directly into new filament.
• The oospore germinates to make haploid thallus of vaucheria.

• According to Williams and his coworkers, concluded that life cycle of vaucheria is haplontic, the oosphere being the only diploid structure.
• Vaucheria thallus is haploid.
• It is aseptate, branched, tubular, aseptate and coenocytic thallus.

Stages in development of sex organ

• Mature sex organ
• Liberation of antherozoids and fertilization
• Fusion of male and female nuclei
• Zygote