Thallopahyta are also known as Thallophyta or Thallobionta. The name “Thallophyta” comes from the characteristic feature of the “thalloid body,” i.e. undifferentiated body. Thallophytes are the most primitive form of plants, mostly found in damp areas or near water bodies.
They belong to the kingdom Plantae and sub-kingdom Cryptogamae. It is placed under this sub-kingdom because it lacks reproductive organs like flowers and seeds. They depend on water bodies for their reproduction as they perform external fertilisation. They consist of further subdivisions of algae, lichen, and fungi.
Characteristics of Thallophyta
Some of the important characteristics of Thallophyta are listed below;
- Their bodies are not differentiated into well-defined stems, roots, and leaves.
- They lack a definite body structure like the higher plants and are unable to move.
- They lack a vascular system, i.e. xylem and phloem for water conduction.
- They also lack cellulosic cell walls.
- They are autotrophic and store nutrients in the form of starch.
- They are found in wet, moist, or damp areas.
- They are the most primitive form of plants.
- They perform external fertilisation with the help of water.
- Sex organs are simple and single-celled.
- The life cycle of algae varies; it shows haplotic, haplodiplontic, and diplontic conditions.
Classification of Thallophyta
Thallophytes are biologically classified into Algae, lichens, and Fungi.
1. Algae
Algae are mainly aquatic organisms (freshwater or marine). They are autotrophic and are capable of synthesising their food. They bear chlorophyll for photosynthesis. The forms and sizes of algae vary. The size of algae ranges from microscopic structures (Chlamydomonas), filamentous (Spirogyra), and massive (Kelp) to colonial (Volvox) forms. They possess flexible bodies that enable them to move with the tides. Their bodies are usually covered by mucus.
They can be classified into:
1. Rhodophyceae
- They are also called red algae due to their reddish appearance.
- They are mostly marine. They contain chlorophyll a, d, and phycoerythrin.
- They store their food in the form of floridean starch.
- Examples are: Porphyra, Polysiphonia, Gelidium, and Gracilaria.
2. Phaeophyceae
- They are also called brown algae due to their brownish appearance.
- They are mostly marine.
- They contain chlorophyll a, c, and fucoxanthin.
- They store their food in the form of mannitol and laminarin.
- Examples are: Fucus, Dictyota, Laminaria, and Sargassum.
3. Chlorophyceae
- They are also called green algae due to their greenish appearance.
- They are found in freshwater, brackish water, and marine environments.
- They contain chlorophyll a and b only.
- They store their food in the form of starch.
- Examples are: Chlorella, Volvox, and Ulothrix.
2. Lichen
It is formed when a symbiotic association between algae and fungi takes place. The algal or cyanobacterial partner is called a phycobiont and is responsible for photosynthesis and the synthesis of food. The fungal part is called the mycobiont and is responsible for providing anchorage, protection, minerals, and water.
Based on Growth form (Thallus) lichens are categorised into three types that are given below:
1. Crustose lichen
- It form a thin crust tightly attached to rocks, bark, or soil.
- Cannot be removed without damaging the surface.
- Appear flat and paint-like
- Examples: Graphis, Lecanora
2. Foliose lichen
- It have a leaf-like and flat thallus with lobes
- Loosely attached to the substrate by rhizines
- It can easily separated from the surface
- Examples: Parmelia, Physcia
3. Fruticose lichen
- This type of lichen is shrub-like or hair-like, cylindrical or ribbon-shaped
- Grow upright or hang freely
- Attached to the substrate at a single point
- Examples: Usnea, Cladonia
3. Fungi
They are non-motile, heterotrophic, spore-bearing, non-vascular plant-like organisms. The fungal cell wall is made of chitin, glucans, and glycoproteins. Their body is composed of finger-like projections called hyphae. A network of hyphae is called mycelium. They lack chlorophyll or any other photosynthetic pigments. Hence, they are dependent on other organisms for food as they live as parasites, saprophytes, or symbionts.
They can be classified into:
1. Phycomycetes
- They are mostly saprophytic or parasitic.
- Their hypothesis is unbranched or aseptate.
- Examples are: Mucor, Rhizopus (bread mould) and Albugo.
2. Ascomycetes
- They are mostly saprophytic, parasitic, or coprophilic.
- Their hyphae are branched or septate.
- Examples are: Aspergillus, Claviceps, Penicillium, and Neurospora.
3. Basidiomycetes
- They are mostly saprophytic or parasitic.
- Their hyphae are branched or septate.
- Examples are: Agaricus (Mushroom), Ustilago (Smut fungus), and Puccinia (Rust fungus).
4. Deuteromycetes
- They are mostly saprophytic or parasitic.
- Their hyphae are branched or septate.
- Examples are: Alternaria, Colletotrichum and Trichoderma.
Note: Lichens and fungi are currently not placed under Thallophyta. Due to their characteristics, Fungi have been assigned a new kingdom of their own, i.e. Kingdom Fungi and Lichen viruses are not placed under any kingdom.
Importance of Thallophytes
Some of the importance of thallophytes are listed below;
- Algae are responsible for fixing half the amount of carbon dioxide and releasing a huge amount of oxygen on the Earth.
- Algae are the source of agar used to make jellies, etc.
- Algae are a source of high-energy compounds in aquatic ecosystems.
- Lichens can act as pollution indicators, i.e. they can not tolerate pollutants.
- Lichen extracts are used for litmus.
- Lichens are the pioneer organisms during ecological succession.