The group of non-mobile polyphyletic living organisms falls under the category of thallophytes. Thallophytes are also referred to as thallophyta or thallobionta. Thallophytes are identified and classified based on the presence of identical or similar characteristics. Although they do not have a common ancestral origin, they are grouped under one class based on other similar features.
The body of thallophytes does not contain a vascular system and hence conducting tissues are absent. The types of living organisms falling under thallophytes include algae, slime moulds, fungus, and lichens.
All the living organisms categorized under the class thallophyta possess a few similar features. The characteristics possessed by thallophytes are as follows:
- Thallophytes do not possess a definite body structure. Unlike plants, they do not possess body structures like stems, leaves, and roots. The body structure is indefinite or undistinguished.
- Thallophytes are generally observed in wet places. This is because they lack a vascular system and true roots that can aid in the transportation of minerals and water. Thus, they’re mostly found in wet places.
- Thallophytes are autotrophs i.e. they prepare their food. They prepare food by the process of photosynthesis. The glucose synthesized by photosynthesis is either consumed immediately or converted into starch. Starch is the reserve food material seen in autotrophic thallophytes.
- However, fungi are the only ones that depend on other living organisms for food.
- The cell wall of most thallophytes is composed of cellulose.
- Thallophytes lack a vascular system. Therefore, there are no conducting tissues available for the transport of water or minerals.
- Thallophytes do not contain xylem and phloem.
- The reproductive organs of most thallophytes contain a single cell and are simple.
- The process of embryo formation is absent in thallophytes.
- The amalgamation of male and female gametes is the mode of reproduction in thallophytes.
- The lifecycle of thallophytes consists of 2 phases - diploid and diplohaplontic. In the lifecycle of thallophytes, the haploid phase is the gamete producing one, hence called the gametophytic phase. The diploid phase is the spore-bearing one, hence called the sporophytic phase.
Classification of thallophyte:
Thallophytes are classified into two categories - Fungi and Algae. Let’s have a closer look at these two sub-divisions of the thallophyte.
- Fungi are achlorophyllous and non-mobile thallophytes. The cell wall of fungi is made up of chitin.
- Fungi are incapable of synthesizing their own food due to the absence of chlorophyll. Thus, fungi depend on other living entities to derive their food.
- One such combination is with the algae. Fungi live in symbiosis with algae since they are chlorophyllous. Algae offer food to fungi while fungi protect algae from harmful UV rays. This type of existence where two organisms support each other’s survival is called symbiosis.
An example of a fungus living in symbiosis with algae is the lichen. Algae and fungi both act as a single unit.
- Algae are chlorophyllous thalloid. Algae, being autotrophic, are capable of synthesizing their own food.
- They are simple and largely aquatic (marine or freshwater). They are found in a variety of habitats such as wood, moist stones, and soils. A few fungi live in association with fungi and animals. Example of algae + fungi: Lichen Example of algae + animal: Sloth bear.
- The sizes and forms of algae are highly variable. The size of algae ranges from microscopic structures to filamentous and colonial forms.
Microscopic fungi - Chlamydomonas Filamentous fungi - Spirogyra Colonial fungi - Volvox
- The mode of reproduction in algae is sexual i.e through fertilization of male and female gametes. Different types of algae undergo different modes of sexual reproduction. For example, Chlamydomonas undergoes isogamous sexual reproduction where both the gametes are of equal size. A few species of Chlamydomonas undergo anisogamous reproduction where gametes are not of the same size. Species like fucus and volvox undergo oogamous reproduction where the female gamete is large and non-motile and the male gamete is small and motile.
Key benefits of algae:
- Algae are of great benefit to humans. Algae are responsible for fixing at least ½ of the total CO2 on the earth.
- They undergo photosynthesis and enhance the amount of dissolved oxygen in their surroundings. They are capable of producing high-energy compounds that act as a foundation for aquatic food cycles.
- Species of algae such as Porphyra and sargassum are used as food materials.
- Agar, derived from gracilaria or gelidium, is widely used in the preparation of chocolates, jellies, and ice-creams.
- A few species like spirulina and chlorella are used as food supplements because they are rich in proteins.