In the semi-arid districts on the south slope of the mountains the flora consists chiefly of dry grasses, acacias, yuccas and cactuses.
White and sweet potatoes, yams, sweet and bitter yuccas, sago and okra, may also be mentioned.
Yams and sweet-potatoes, yuccas, malangas, cacao, rice - which is one of the most important foods of the people, but which is not yet widely cultivated on a profitable basis - and Indian corn, which grows everywhere and yields two crops yearly, may be mentioned also.
There is a close relation between the pollination of many yuccas and the life of a moth (Pronuba yuccasella); the flowers are open and scented at night when the female moth becomes active, first collecting a load of pollen and then depositing her eggs, generally in a different flower from that which has supplied the pollen.
The most common plants of the Mexican plateau are the agaves, yuccas and cacti, each of which is represented by a number of species.