A little more information:
Dandelions are thought to have evolved about 30 million years ago in Eurasia. Fossil seeds of Taraxacum tanaiticum have been recorded from the Pliocene of southern Russia. Dandelions have been used by humans for food and as an herb for much of recorded history. They were well known to ancient Egyptians, Greeks and Romans, and are recorded to have been used in traditional Chinese medicine for over a thousand years. The plant has been used as food and medicine by Native Americans. It is likely that Dandelions arrived in North America on the Mayflower—not as stowaways, but brought on purpose for their medicinal benefits.