Hint:-Thallophyta is a division which includes a group of plants like algae, lichens, fungi etc. Basically, it involves a group of plants that does not possess roots, stems or leaves. They are also non-motile organisms; they sometimes also include bryophytes, bacteria and slime moulds.
Complete answer: Thallophyta includes a group of plants that are non-embryophyte, non-motile, and also they do not possess stems, roots and leaves as mentioned above. These plants grow mainly in water. Major group of thallophytes contributes to marine ecosystems. It is the most primitive and largest division of cryptogams. Their body is not differentiated into leaves, stems and roots hence they are called thallus. They can be unicellular or multicellular, but they have autotrophic mode of nutrition some of the examples are Cladophora, Chara, Spirogyra etc. They have cellulose cell walls around their cells, their size may range from microscopical unicellular like Chlamydomonas to colonial forms like volvox even to filamentous form. Algae cells have a covering of mucilage that protects it from decaying in the water, desiccation and epiphytic growth. Due to their aquatic habitat they do not require water conduction thus they do not possess vascular tissues that are xylem and phloem, Mechanical tissues are also absent hence they are flexible. Some more examples are Batra, Polysiphonia, Fucus, Sargassum etc.
Note:- Algae are chlorophyll bearing thus it prepares their own food and is autotrophic that have photosynthetic pigments for example carotenes, chlorophylls and xanthophylls. They can reproduce by vegetative reproduction, asexual reproduction or sexual reproduction which includes isogamous, anisogamous and oogamous types.