What is the most common type of vegetation in southwest and central asia

Desert Scrub.

Explanation:

Desert Scrub normally refers to a desert biome. However, it can also be used to describe several types of plants that grow on these habitats, such as the creosote bush or the rabbitbrush, and others.

These types of plants are capable of withstanding environments with very little precipitation like the southwest and central regions of Asia, which is mostly covered by great extensions of desert biome.