Current vegetation maps show evergreen forests of Cambodia as one homogenous forest type. However, ecological field studies in the central plains demonstrated a heterogenous mosaic of different evergreen forest types, each with a unique species composition and ecological characteristics. Based on six botanical expeditions, we describe four lowland evergreen forest types: 1) riverine forest dominated by Dipterocarpus costatus (Dipterocarpaceae); 2) tall dipterocarp forest dominated by Anisoptera costata (Dipterocarpaceae); 3) swamp forest dominated by Macaranga triloba (Euphorbiaceae); and 4) ‘Sralao', an open forest with a monodominance of Lagerstroemia cochinchinensis (Lythraceae). Ordination by non-metric multi-dimensional scaling (NMDS) indicated that the four forest types represent well-separated floristic entities with Sralao as the most deviant community. The highest species diversity was found in the riverine forest (urn:x-wiley:0107055X:media:njb12662:njb12662-math-0001 = 2.65), followed by tall dipterocarp forest (urn:x-wiley:0107055X:media:njb12662:njb12662-math-0001 = 2.53) and swamp forest (urn:x-wiley:0107055X:media:njb12662:njb12662-math-0001 = 2.34), whereas the Sralao forest had the lowest species diversity (urn:x-wiley:0107055X:media:njb12662:njb12662-math-0001 = 1.64). We argue that botanical fieldwork remains essential to refine vegetation maps otherwise based on remote sensing, and that knowledge of species composition is essential to conserve Indochina's vanishing evergreen forest biodiversity.