Large cactus native to arid Earth environments.—In-game description
These cacti flourish in dry biomes, like arid shrublands and deserts. Natural to extreme desert as well but cannot be planted by humans unlike all other variants. They can be chopped down for a minimal quantity of wood, but as you aren't likely to find that many logs in such an environment, saguaro can be an important resource for you.
The Saguaro cactus also has a history in RimWorld of being able to provide a modicum of cover for pawns during a firefight.
Real-life saguaro cacti produce ruby red fruits that are about 6-9 cm long, which are edible and highly prized but require a pole or other implement to harvest. These fruits are used by a group of Native Americans called the Tohono O'odham, who brew them into a fermented drink and use it during ceremonies to summon rainstorms.