Cactus

Cactus is a block that is only available in Alpha mode. It was first seen in the Secret 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 broken easily without any tools.

It appears on Sand in vertical of stacks that can be 1 - 3 blocks tall, 1x1 wide. They are somewhat rare, and appear in normal and winter themed maps. When the player touches the block, half a heart of damage is taken and when an item is thrown at the cactus the item disappears. Half a heart of damage is taken for each Cacti block walked on; for the player and mobs. This makes it useful for traps, such as a hallway with Cactus block floor. If any mobs to walk into the hall, the floor will kill them quickly. When mined, it drops 1 cactus block.

Since Secret Friday Update 6, cacti can only be placed on sand with no horizontally or vertically adjacent blocks, however they can be placed next to one block if placed in water. Blocks can be placed diagonally next to them. When the spot they are placed in becomes unsuitable (e.g. a block is placed next to them), they collapse into a cactus block and can be re-placed. As well, mining cacti no longer harms the player.

Cactus blocks are farmable. A single cactus block placed on sand will grow to a three-block plant after a set amount of time. They seem to grow on their own in summer worlds, but winter worlds may require torches to be placed near them. 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 isn't advisable; if the dropped cacti blocks touch the bottom section, they get destroyed too).

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

New cactus after the 23rd, July update.