Sinharaja is characterized by its remarkable vegetation, presenting itself as a tropical lowland rainforest or tropical wet evergreen forest. The dominant trees in this forest stand tall, with straight boles and a striking height ranging from 35 to 50 meters. The forest showcases a high degree of endemism, particularly within the Dipterocarpaceae family, where more than 90% of species are unique to the region.
The untapped genetic potential of its flora is immense. The forest comprises layers of vegetation, with a density of approximately 240,000 individuals per hectare, predominantly in the ground layer. Tree density ranges from 600 to 700 individuals per hectare, with a smaller number of merchantable trees.