Answer: They lived in water.
Step-by-step explanation:
The earliest ancestors of plants lived in water. Having seeds, having no competition and and having seeds are modern characteristics of the plants.
The earliest characters of the plants is that they lived in the water. Previously the planet was covered with water and the plants was limited up to water only.
They needed water for fertilization. After a long-long time they moved towards land and angiosperm and gymnosperm evolved.