In the late Ordovician Period, small insignificant land plants first appeared. During the Paleozoic Era, the spread of land plants caused a green revolution over the surface of the globe. Plants help to break down rocks and contribute to their own decaying remains to create rich protective soils. Before plants invaded the land there was no soil as we know it. Plants actually prevented erosion by binding soil with their roots and retaining runoff water.
Most early plants are preserved as a thin carbon film in the rocks. These specimens have retained their three dimensional structure. Vascular cells are clearly visible when the stems are examined under a microscope. The first land plants such as Cooksonia were simply stems with spore on the tips. The spores were very fragile and came off easily. Cooksonia was one of the first plants to actually look like the common plants that we have today. They had a plant body, stiffened outer tissues free release like spores,a waxy outer covering to prevent moisture loss, and special pores and stomata to release gases. Early plants reproduced by spores. Spores are tiny, light, and have thick protective walls. They easily spread by wind and water. The first known spores are four-hundred million years old.
All of the early land plants were thought to be descended from the organisms called Chlorophyta which means Green Algae. This algal plant has more extant species than any other plant. Chlorophyta members have chlorophyll a and chlorophyll b which are the same as it's own. Members of Chlorophytas range from unicellular to multicellular organisms and have a wide range of habitats. At least two groups of Chlorophyta have been thought to be ancestors of the land plants. Some of the land plants have been thought to belong to the group Coleochate a .
sources:
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The First Land Plants