Lundy Cabbage - it might not look like much but this small yellow plant grows nowhere else in the world apart from Lundy Island having evolved into a separate species in the 9,000 or so years that Lundy has been isolated from the rest of Devon. Not only is this plant unique but it supports two species of beetle that live on no other plant. Truly it is a micro-ecosystem!
If you view full size you can see a beetle on the flowers - it might be a very rare beetle!
See:
http://en.wikipedia.org/wiki/Coincya_wrightii