What evidence is there to support past plant migration?

Answer 1

Volcanic islands rise up from the oceans, and eventually plants colonize these new islands. Look at Hawaii or the Galapagos. They are volcanic islands that have plant life due to migration.

Answer 2

Actually plants distribute themselves to as far as environment permits them. Plants that hibernate during cold(freezing) conditions can colonize further north than plants that suffer frost damage.

Vast ice sheets of the ice age have scoured some cold adapted plants off the face of the earth, but microclimes on mountain ranges allow Northern climate adapted plants to have further southern growth ranges.

Relic populations of Sequoia in California and Meta Sequoia in China plus the fossil record give evidence of their once world wide distribution.

Human enabled migration is easily documented on some of the food crops. Corn can be traced to Central America and using genetic evidence, pollen samples and fossil remains will show human intervention on the distribution of corn.

Actual plant migration is agonizingly slow. In the fungi kingdom, fairy rings is caused by mushroom mycelia that extend outwards from a central spot. After a hundred years the fairy ring may only grow as large as 200 feet in diameter. The mycelia will inch along over the years literally....