To give them a large surface area to soak up water, because water is scarce, they need to take up as much as they possibly can.
Barrel cactus have fibrous roots
Cactus have fibrous thread like roots so they can absorb water even in the smallest quantity.
Because the roots of the saguaro cactus are just below the surface.
it has long roots that edge into the ground so deep that they can find water and feed
Some cacti have shallow roots. Other cacti have long tap roots.
Yes, the barrel cactus has roots.
Yes, a saguaro cactus has roots.
long rooted system and scatterted underground
Cactus are a desert plant, and so need to send their roots deep down for their food.
Cactus plants use their stems for storage. So that's where starches are stored. In fact, stems are where a cactus plant stores everything. Other, non cactus plants may use their roots for storage. But cactus roots are much too fibrous and shallow.
A Cactus has roots to absorb as much water as possible when it rain also to support the Cactus when it bad weather such as wind.
when the cactus is none of sun it can survive