Vaucheria: Classification, Structure and Reproduction

Table of Contents

Vaucheria is a yellow-green alga that belongs to the class Xanthophyceae. It is commonly known as the water felt. This species is found worldwide, most existing in freshwater and marine environments. Some of the species are terrestrial as well. They can be commonly seen in estuaries, salt marshes, ponds and wet farmlands. Around 54 species of the genus are known, out of which 9 are found in India.

Classification of Vaucheria

Structure of Vaucheria

• The plant body of Vaucheria is filamentous, branched, coenocytic, and siphonaceous thallus.
• They are mostly aseptate in structure, but septa may form during injury or development of sex organs.
• The terrestrial species of Vaucheria are found attached to the soil substrate by rhizoids. However, the floating species have no or ill-developed rhizoids.
• The filamentous body of Vaucheria has a thin outer wall, which is less elastic in nature.
• It has an outer layer made of pectin and an inner layer made up of cellulose.
• Inside the filament, a central vacuole is present with cell sap at the apices.
• The filament has a protoplast that is present between the cell and the vacuole. The protoplast houses nuclei, chromatophores and other organelles.
• Chromatophores are elliptical or disc-shaped chloroplasts that contain pigments but lack pyrenoids.
• It contains pigments, such as chlorophyll a, chlorophyll e, xanthophylls and carotenoids.
• Food is stored in the form of oil and can be seen as colourless droplets in the cytoplasm.

Reproduction in Vaucheria

Vaucheria reproduces by vegetative, asexual and sexual means. Let us look at them one by one.

Vegetative Reproduction in Vaucheria

Vegetative reproduction in Vaucheria takes place by fragmentation. The filaments of the genus may break due to mechanical injury by insect bites. Septa is formed at the site of injury, and the broken fragments develop into a new thallus.

Asexual Reproduction In Vaucheria

Asexual reproduction in Vaucheria takes place in three ways:

1. Aplanospores: Aplanospores are non-motile spores that are formed singly inside structures called aplanosporangium. They are formed during unfavourable conditions at the apical side of aerial hyphae. The aplanosporangium are club-shaped and non-flagellated structures that are separated from the rest of the thallus by a transverse septum. The aplanospores rupture the cell wall of the aplanosporangium and develop into new filaments.
2. Zoospores: Zoospores are flagellated asexual spores that are borne singly inside zoosporangium. Zoosporangia are green-coloured and club-shaped structures that are formed at the apical region of the filaments by forming a cross-wall from the rest of the filament.

At the time of the liberation of the spore, the protoplast of the zoosporangium contracts, forming a narrow aperture, from which the zoospores are released. The zoospores become flagellated after liberation. The zoospores are yellowish-green, multiflagellate, multinucleate and ovoid structures that have a small central vacuole. They are also referred to as compound zoospores.

3. Akinetes: Akinetes are formed by the division of filaments into small segments by a thick gelatinous wall during unfavourable conditions. The akinetes are small, multinucleate and thick-walled segments that are also known as cysts or hypnospores. Since the segmented filament resembles the genus of Gongrosira algae, this stage is also known as the Gongrosira stage.

Read: Difference between Sexual and Asexual Reproduction

Sexual Reproduction In Vaucheria

Sexual reproduction in Vaucheria is of oogamous type. The male sex organ is known as antheridium, and the female sex organ is known as oogonium. The plant body of Vaucheria can either be homothallic, meaning both the male and female sex organs are borne close to each other, on the same filament, or heterothallic, such that male and female sex organs are borne on different plants.

Development of Antheridium

For the development of antheridium, a short lateral branch projects out of the Vaucheria filament. The branch is aggregated with nuclei and chromatophores in the apical region. The apical region of the branch then bends into a horn shape, and a septum is formed. This separates the antheridium from the rest of the filament.

Inside the antheridium, the nuclei divide mitotically and give rise to biflagellated and spindle-shaped antherozoids. The flagella are dissimilar, i.e. one is whiplash and one is tinsel. The antheridium opens at the apex, and antherozoids are released.

Development of Oogonium

The base of the antheridial branch develops a protuberance due to the accumulation of cytoplasm. This region of cytoplasm is colourless, has abundant nuclei and lacks chromatophores; this multinucleated mass is referred to as wanderplasm. The wall of the wanderplasm bulges out to form an oogonial initial, which enlarges eventually, and a number of chromatophores migrate in this area.

The oogonial initial further develops into an ovoid or round-shaped structure with a beak at the apex. They get separated by the formation of transverse septa. During development, all of the nuclei in the oogonium, except one: degenerate. This one nucleus forms the ovum or the egg.

Fertilisation

At the time of fertilisation, the beak of the oogonium ruptures, and an aperture is formed in the antheridium. The oogonium releases a small amount of cytoplasm through the ruptured beak, and as a result, many antherozoids get stuck in the liquid, but only one enters the oogonium. The antherozoids lose their flagella upon coming in contact with the ovum and fuse with it to form a diploid zygote.

Germination

The zygote that is formed inside the oogonium comes out and remains dormant for some time. Upon the arrival of favourable conditions, the zygote divides meiotically and mitotically to form a coenocytic structure. The zygote wall cracks at some point, and the protoplasm elongates to give rise to rhizoidal initial and aerial hyphae.

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