https://minecraft.fandom.com/wiki/Minecraft_Dungeons:Poison-Quill_Vine

Poison-quill vines slightly resemble quick growing vines in appearance, but instead of having a pointy end and being covered with spikes, it has a purple-coloured flower head that it can open to shoot poisonous quills, and close it at will.

It can also be summoned by whisperers. Unlike quick growing vines, they stay in one place instead of retreating back to the ground, unless summoned by a whisperer, where it will sink into the ground after a few seconds.