What is the Evolutionary History of Plants?

The evolutionary history of plants begins a very long time ago. Algae has probably existed on moist ground for over a billion years, but plants, as in the kingdom Plantae, did not emerge until 700 million years ago at the earliest. This number is from molecular genetics analysis that suggests land plants split from the green algae around this time, although this figure is not corroborated by fossil evidence. The earliest evolutionary history of plants on land appears in the early Ordovician period, about 475 million years ago, although many paleobotanists suspect there were plants during the Cambrian period, 500 million years ago. The first land plants were non-vascular bryophytes, represented today by mosses, hornworts, and liverworts. These plants, lacking circulatory tissues, were quite short, between 1 and 100 mm (4 in) in thickness. These bryophytes represented the basal group in the evolutionary history of plants. They could only survive in very moist areas, where all cells can ...  more