Plantae are defined as multi cellular organisms which produce their food by photosynthesis. They are also known as metaphyta. Mainly in the old classification plant kingdom is divided into three groups which are thallophytes, bryophytes and tracheophytes. Thallophytes include fungi and algae. In this group there is formation of thallus which is non vascular and non differentiated part. There is no embryo formation. In the new classification of plant kingdom thallophytes are not included. It includes algae, bryophytes and tracheophytes. Algae are aquatic and do not have embryo stage. But bryophytes and tracheophytes have an embryo stage and are known as embryophyta. These types occur on land. Tracheophytes are also known as vascular plants. Vascular plants are further divided into pteridophytes and spermatophytes. Pteridophytes are seedless vascular plants while spermatophytes are vascular plants with seeds. Plant originated under water where the sea connects to the land. In the sea most of the organisms are photosynthetic and unicellular. They are restricted up to 200m of the sea. This is referred as photic region. The remaining plants which are below this level are of decomposer type as there is no light available for the process of photosynthesis. Algae play an important role for the evolution of terrestrial plants. So they are more primitive as compared with plants.
What Is Kingdom Plantae?