Abstract: The thorny succulent thrubs in dry-hot valley of Yuanjian county are special secondary shrubs with the characters of tropical desert vegetation. The shrubs distribute mainly in the area below alt. 600 m in the valley and grow on the drier and hotter rocky banks. The succulent genera Euphorbia and Opuntia together form the upper synusia of the shrub layer of the community and other many dry-hot resistant shrub species form the lower layer. Under the several human disturbances to the natural vegetation and malpractice, cultivated Euphorbia royleana and Opuntia monacantha intruded into the semi-savanna of the valley and formed the thorny succulent shrubs. The shrubs may be accepted as an association which can be divided into two subassociations. The flora of the shrubs has direct affinity with the xeric flora of tropical Asia and is considered to have the conne-ction with Gondwana flora in its origin. With the continuation of severe human disturbance to the natural vegetation and malpractice, ecoclimate would become drier and hotter and the secondary shrubs would continuously develop in the valley.

Key words: Dry-hot valley