By+Li+SU　+Painted+by+Wang+Ying

Animals can migrate， peple can move the residences. The plants seemingly not able to move will also advance with small steps in the generation after generation. After tens of millions of years， they will also be the brave who make an arduous journey.

The history of plants migration is glorious and tragic. In order to recover these histories， the botanists exhausted their ideas. Firstly， they have to correctly identify the plants family pedigrees. For humans innate psychology， people all over the world tend to divide the living things into movable animals and unmovable plants. Even in biology， this simple dichotomy has been used until the 20th century. With the development of molecular systematics， the scientists finally established accurate system evolution relationships for cell biologies around the world.

According to the different cell structures， all cell biologies are firstly divided into three “domain”——the original nuclear domain， ancient nuclear domain and eukaryotic domain. Algae belongs to the original nuclear domain， and is the close relative of bacteria. Eukaryotes can be divided into two branches， the backbone family of one branch are animalsand fungi. In other words， the mushromms and black fungus once though as plants are actually distant relatives of animals. The other branch contains a variety of algaes， the “ancient plastid class” are consisted of gray cell algae， red algae and green plants. Todays “plant” in taxonomy usually refers to the green plants， only including the aquatic algae and chara， and the terrestrial bryophytes， clubmosses plants， ferns， gymnosperms and angiosperms.

There is no doubt that the ancestors of green plants are from the sea. According to the calculation， the green algae has origined since the archean about 1.5 billion years ago. It has been thriving in the ocean for hunderds of millions of years， witnessed the Cambrian Marine “l(fā)ife outbreak”， and conquered the land combined with lichen. By the ordovician of 400 million years ago， the green algae has evolved into a more complicated land plants， the vast land was finnally covered by green.