The plant is a living being, provided generally with many parts, called organs, which it uses for taking in nourishment, for breathing, for protection against its enemies, and for reproducing itself and so keeping up the numbers of its own kind. There are different types of plant species, which are found on planet earth. They are sorted and classified into a separate kingdom known as Kingdom Plantae and this classification is based on their similarities and differences.
Plants 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 200 meters 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.
There are over 280,000 species of plants on Earth which are estimated to have evolved from green algae 450-630 million years ago. The fist plants to evolve where similar to mosses and reproduced using spores, an adaptation to being on land. Over time, selection favored plants that could tolerate dry land which lead to seed evolution. Plants with true seeds evolved around 390-320 million years ago. As selection began to favor plants with seeds a new adaptation was seen, flowers and fruits, around 130-200 million years ago. Some flowering plants have adapted to live back in the aquatic environment from wince they first evolved.