Abstract
1) About 250 species of the pteridophytes known in northern Thailand are arranged according to the distribution patterns and altitudinal occurrences. The Sino-Himalayan elements are predominant in the evergreen forests at higher elevation. Separated by the broad belt in Central Plain and Korat Plateau, Thailand is divided into two floristic regions which match well with the climatic division. No special floristic division is recognized for the pteridophytes of Thailand. 2) Doi Inthanon and Doi Chiang Dao are the mountains rich in the species of the pteridophytes. These two mountains are different from each other in edaphic and physiographic conditions. The pteridophytes of these two mountains are compared in details, and are concluded that their occurrences are generally speaking as the result of the ecological factors, especially under the influence of the climatic condition. 3) The habitats are peculiar within Thailand for several species. They are interpreted as the result of the ecological condition, especially of the presence of moisture.
