Two zones of semi-arid climate are recognized in India, one in the north contiguous with the desert of Thar, extending into Rajasthan, the Punjab and North Gujarat and the other in parts of the Deccan and Madras State in the south.
Analysis of the flora of these regions reveals that seventeen types of floral elements are represented in these semi-arid zones. The Southern zone has higher percentages of the Indian element and, to some extent, of the Indo-Malayan. On the other hand, the northern zone is richer in the North African-Indian Desert (Saharo-Sindian) element. North African Steppe element and in the Mediterranean-Oriental element. The elements of tropical and warm countries as well as the cosmopolitan element are equally frequent in both the zones. The percentage of the endemic element is very low in these regions, not exceeding 2.5%.
The pattern of distribution of these floral elements is explained on the basis of the bioclimatic conditions prevailing in the Afro-Asian continents.
Finally, it is shown that contrasting seasonal aspects in the annual cycle of the climate—the alternation of a very long dry period with a short rainy season and of a cool and short-day winter with a hot long-day summer—permit the development of several floral elements.