The ancestors of plants are most likely plant-like protists, which are small, unicellular, aquatic eukaryotes capable of photosynthesis. These organisms gave rise to land plants about 475 million years ago. The first land plants were simple and did not contain vascular tissue. This meant that they were not able to move food and water from one part of their structure to another. Examples of these nonvascular plants are seen in liverworts, hornworts, and mosses. All three groups are small, simple, and must live in moist environments.
The third major evolutionary development in plants occurred around 360 million years ago. Plants developed seeds. These seeds are used for reproduction and provide several advantages over plants that do not have seeds, including the ability for offspring to travel far distances from their parents, protection from the elements, and the ability to remain dormant until the time is just right to grow. Examples of plants that produce seeds are conifers, daffodils, and apple trees.
Around 420 million years ago, a great advance in plant structure evolved - vascular tissues. The two types of vascular tissue - xylem and phloem - move water and food throughout plants. This development allowed plants to expand where they could live - they no longer needed to be in only moist environments. It also allowed them to grow bigger. This adaptation was so advantageous that more than 90% of all plant species are vascular. Examples of vascular plants include ferns and horsetail.
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