In this region, although it rarely rains the fog provides moisture sufficient to nurture a great deal of grassland, shrubs and thick woodland. There are over sixty local species of plant. This coastal strip is of particular importance as further inland where the fog does not have an influence most of the Arabian Peninsula is desert. Vegetation varies progressively away from the coast which features dense woodland of Anogeissus dhofarica, Acacia senegal and various thorny Commiphora trees and shrubs. The richest flora can be found in the Dhofar mountains which have 900 plants including 60 endemic species and two endemic genera, Cibirhiza and Dhofaria. One of these plants, the frankincense tree (Boswellia sacra) was a source of great wealth for Dhofar in antiquity. In Yemen the side of Jabal Urays facing the sea is covered with Euphorbia balsamifera shrubs.