Deathweed

Deathweed appears as a short double stalk of corrupted grass with sickly green bulbs at the ends. It grows in The Corruption, on Ebonstone or corrupted grass, and can be cut by any weapon or tool. It can also be planted in Clay Pots by using Deathweed Seeds.

Deathweed blooms during a Blood Moon or when under the light of a Shadow Orb, and this is the only time that it will drop 1-3 Deathweed Seeds when cut. Deathweed uncommonly blooms during the day and does not drop Deathweed Seeds.

Trivia

 * This could be a reference to an in-game item in the highly successful MMORPG, World of Warcraft. However you can no longer find deathweed in World of Warcraft.