Taman Negeri Selangor is the source of the major rivers in Selangor. These rivers begin as small streams deep in the forests of the Park. Streamside forests, also known as Saraca-streams, are particularly well developed in the southern half of the Park.
The Saraca, or Gapis tree, Saraca cauliflora (Bean family Leguminosae), are common along the stream beds. Their latticework root systems cover the stream banks, protecting the banks by slowing down the flow of the river, particularly after heavy rains. The root-work also provides habitats for small anthropods including prawns. The Saraca trees are a beautiful flora species of the Park.
Young gapis seedlings can be seen in along the sand banks of the streams.