Cactus

Cactus is a block that is only available in Alpha mode. It was first seen in the Seecret Friday Update 5, about Minecraft Alpha version 1.0.5_01. The block has one texture put on all sides of the block, one put on the top, and a third on the bottom of a cactus cross-cut. It can be mined easily without any tools.

It appears on Sand in vertical stacks that can be one to three blocks tall, 1x1 across. Cacti are somewhat rare and appear in both normal and winter-themed maps. When the player touches a cactus, half a heart of damage is taken, and when an item is thrown at a cactus the item disappears. This is also true if the cactus forms a floor: both players and mobs take half a heart of damage when they walk on a cactus block. This makes it useful for traps, such as a hallway with a cactus block floor, which will quickly kill any mobs that walk on it.

Since Seecret Friday Update 6, cacti can only be placed on sand or other cactus blocks with no horizontally or vertically adjacent blocks, unless they are placed in water, in which case they can be placed directly next to one other block. Cacti are also able to grow without light. When the spot a cactus is placed in becomes unsuitable (e.g. a block is placed next to them), it collapses into a cactus block that can be collected and re-placed. However, mining cacti no longer harms the player as of this patch, so the player can gather cactus blocks more quickly through ordinary mining. Each mined block of cactus drops one cactus block.

Cactus blocks are quickly farmable. A single cactus block placed on sand will grow to a three-block plant after a set amount of time. Snow on top halts growth, so either a roof or a nearby heat source is required to grow cacti on a snow map. Like Reeds, removing the bottom part causes all parts above it to be removed as well, allowing for quick harvesting; one can also "shave" off the upper sections and leave the bottom section planted, but this is not efficient when mining cacti, because any dropped cactus blocks that touch the bottom section will be destroyed, just like any other thrown or dropped block that touches a cactus block. Swords can be used to speed up harvesting, but each cactus will consume two of the sword's uses.

It is possible that cactus blocks will serve more purposes in the future.

Cactus blocks are non-flammable.

A way to make a tall cactus tower is: When the cactus is fully grown, place a block of sand on top. Then, place a block of cactus on the sand.

New cactus after the 23 July update.