The four regions have no administrative significance, but each differs from the others in population, basic resources, natural features, and level of social and economic development. The geological formation is generally of sandstone or granite. Both historically and in recent times, northern Thailand has received the most attention of botanists who collected bryophytes. The division includes four natural regions and 18 provinces.
Floristic affinities are close to southwestern China as well.
The region is the high plateau of Thailand. Types of forests are from dry deciduous to mixed deciduous forests with large tracts of dry evergreen forests growing intermittently. Pine forests are present from above 1000 m. Dipterocarp forests are the common feature of the region. A significant number of bryophytes have been collected from this region.