THE IMPRESSIVE OLYMPOS GORGE and THE ROUTE TOWARDS PETRA PATHS. An impressive diversity of vegetation characterizes the gorge. Here you will see more than 1700 plant species (25% of Greek flora) out of which 23 are indigenous. In lower altitude you will see bushes (arbutus, holm-oaks, cedar trees) and deciduous trees (fraxos, squills, plane trees). On the highest altitudes grow black pine trees, beech trees and robolo (the southest point of its growth).