Which of the following is a natural vegetation of desert regions?

Concept

Natural vegetation is classified by the climate of a region — mainly the amount and pattern of rainfall — into types such as tropical evergreen forest, tropical deciduous forest, thorn/desert (xerophytic) vegetation, temperate coniferous forest, and mangroves. Deserts and semi-arid tracts receive very low, erratic rainfall, so their natural vegetation is made up of xerophytes: plants structurally adapted to conserve water — thick, fleshy, water-storing stems, spines or reduced leaves in place of broad leaves (to cut down transpiration), deep or widely spread roots, and a thick waxy cuticle.

Applying it here

A cactus stores water in its thick, fleshy stem and bears spines instead of leaves, exactly the structural adaptation that lets a plant survive the scarce, unreliable rainfall of a desert — so it is the natural vegetation of desert regions.

Why the other options are not desert vegetation

• Mahogany is a tall hardwood that needs abundant, well-distributed rainfall through the year, so it grows in tropical evergreen (rain)forests, not arid tracts.

• Fir is a coniferous softwood tree of cold temperate and montane climates (e.g. the Himalayan slopes), the opposite climate zone from a hot desert.

• Sandalwood grows in tropical dry deciduous forests, which still receive a moderate seasonal monsoon — far more rainfall than a true desert gets.

Cross-check

Only the cactus shows the succulent-stem-and-spine adaptation that defines xerophytic desert vegetation; the remaining three all belong to wetter forest biomes (evergreen, montane-coniferous, and dry-deciduous respectively), which confirms cactus as the answer.