What Type of plant is a cactus?

Answer 1

The cactus is more likely to be a very tall weed not tree even though most people consider it to be a tree.

From 17wolf359:

A cactus is a succulent plant. As the saying goes, "all cacti are succulents, but not all succulents are cacti". A succulent plant either stores water in it's roots, stem, or leaves. Cacti store water in their stems (and sometimes in their roots). Generally speaking, cacti do not have leaves (with only a couple of exceptions out of thousands of species). Cactus range in size from button size to massive trees weighing many tons.

In evolutionary terms, cacti are some of the most advanced plants on the planet, mostly because of the "areole". The areole is the part of a cactus that spines come from. The areole also produces branches and flowers and is exclusive to cacti. The cactus is also originally a "new world" plant, which is where it evolved. One species of cactus did make it to Africa, most likely spread there by birds. Cacti live in deserts and jungles, on the equator and as far north as Canada (and as far south as Patagonia).

Cacti have now naturalized in many parts of the world because of man and in some places like South Africa and Australia have become weeds.

A cactus is a xerophyte. It's a type of plant that takes in very little water and lives in a dry habitat.