Geographical distribution of sampling points of C. parthenoxylon in Vietnam. Study area (a); adult plant (b). (Zone 1: Red River Delta; Zone 2: North East; Zone 3: North West; Zone 4: North Central Coast; Zone 5: South Central Coast; Zone 6: Central Highlands; Zone 7: South-East; Zone  8: Mekong River Delta (This map does not show offshore islands).