The Sapi Association is extensive:
in swamps along the major rivers of the east coast,
in the lower reaches and estuaries of the Sugut, Labuk, Klagan, Sapi, Kinabatangan and Segama,
on the west coast it occurs in minor valleys, notably between Menggatal and Telipok.
The swamps are often under water. The soils are mainly formed on fine-textured alluvium.
The Sapi Association is formed in backswamps, many of which are in embayments enclosed by hills at considerable distances from the major drainage. In addition, external drainage is impeded by broad levee zones on the main rivers, such that water tables in the backswamps are above or near the surface throughout the year. In the Dent Peninsula, swamps occurs behind coral beaches.
Swamp forest which cover the association comprise low trees, often with pneumatophores and stilt roots; there is dense undergrowth of small bushes, grasses and sedges. A plot described north of Kinabatangan near Kuala Koyah had irregular canopy with the larger trees (e.g. Vitex pubescens, Dialium sp. and Kibessia galeava) reaching 36 m; an intermediate upper canopy at 18-30 m with smaller trees (e.g. Glochidion hypolencum and Dillenia sp.) as an understorey.