Cactus

A Cactus (plural Cacti or Cactus) is a plant block that occurs naturally in deserts and mesas.

Obtaining
Cacti can be mined by hand without taking damage. The tool used to mine the cactus does not affect the speed in which it is mined.

When the spot a cactus is placed in becomes unsuitable, such as when a solid block is placed next to them or their own sand block underneath is harvested or falls, the cactus block will uproot and will drop as an item.

Natural generation
Cacti naturally occur in desert and mesa biomes. They mainly generate as one, two, or three blocks tall.

Farming
Cacti grow only on sand at a rate of one cactus block every 2-4 minutes, and to a maximum height of three blocks; though, higher stacks can be placed by the player. Cacti can only be placed either on sand, red sand, or on other cactus blocks, with no horizontally adjacent solid blocks. Bone meal does not work on cacti to speed its growth. Cacti do not need light to grow and are non-flammable.

Usage
When any entity, including players and mobs, touches a cactus, damage is taken every 0.5 second. Damage from touching a cactus is reduced by armor, but touching it also damages the armor.

Cacti will also destroy any items that come into contact with them, including cacti blocks harvested above them.

When a minecart hits a cactus block, the minecart is dropped as an item - this item is often destroyed as a result, although a hopper will pick it up faster.

Trivia

 * Cacti are not quite a full block wide (7/8 of a block), similar to chests.
 * The bottom of a cactus block does not damage the player.
 * Cacti can be placed underwater, provided they are placed on sand, and will grow if they break the surface.
 * Cactus can be placed next to saplings, but the cactus will break when the tree grows.
 * It takes about 18 seconds for a player to die from cactus (without armor) if the player has full health and the hunger bar is full.
 * Endermen can move and place cactus. Thus, they can increase the cactus population in deserts by moving cactus blocks as they grow.
 * Signs can be placed on the top of cacti.
 * It is possible for cactus to generate on the blocks other than sand due to generated structures.
 * Cactus can be used in the desert to see if you are in a newly generated area. If most of the cactus around you is only one block high, then it is most likely new land.
 * If a player dies of cactus damage, then the displayed death message will read "[player] was pricked to death".

Gallery
Kaktus Cactus Cactus Cactus サボテン 선인장 Cactus Kaktus Кактус 仙人掌