Thorn Weed

From the Super Mario Wiki

Thorn Weeds are a sub-species of Seed Weeds found in Ancient Waterworks, old ruins in Wario: Master of Disguise. The Wishstone turned some Seed Weeds into walking plants with spiky heads. The spikes are so heavy it can't move without firing off a few of the first. That is the way these plants attack Wario-they fire their spikes at Wario and Wario must avoid them.