A cactus is a natural resource that generates on the surface of a desert world, where it can appear singly or as large saguaros. This item occupies one square block and has no collision.
How to Obtain
You can mine cacti on any desert world. Also, in non-desert worlds, two borked cactus blocks generate in the dirt slightly to the side of each painting dungeon.
How to Use
Cacti are purely decorative, offering a nice spiky green touch to any build. Note that cacti only place as single block sized plants, and cannot be reconstructed back into their larger tree-like forms.
Cacti were introduced in June 2013 as part of the 1.9.9 server release.