The plant that has fossils found on widely separated landmasses is Glossopteris.

Here's why this is significant:

* Distribution: Glossopteris fossils are found in South America, Africa, India, Australia, and Antarctica. These continents were once joined together in a supercontinent called Pangaea.

* Evidence for Continental Drift: The presence of Glossopteris fossils on these now-separated continents is strong evidence for the theory of continental drift, as proposed by Alfred Wegener. This theory explains how the continents have moved over millions of years, and the distribution of these fossils supports that movement.

Let me know if you'd like to know more about Glossopteris or continental drift!