The Usukan Association occurs on the coast and islands. There are notable developments on:
Pulau Labuan,
Kuala Penyu,
Pulau Mangalum,
Pulau Mantanani Besar,
the Sandakan Peninsula,
adjacent islands from Libaran in the North to Berhala, is extensive in bays and estuaries, and
east coast of the Dent Peninsula.
The association is formed on beaches of calcareous alluvium; many beaches are formed of coarse-textured coral debris and coralline sand.
Most of the association has been plated with coconuts, the undergrowth being poor heathy grasslands. In the swamps, the vegetation comprises of low trees with climbers, sedges and grasses.