Crimthorn

Crimthorn is The Crimson's most aggressive form of terraforming. It can begin growing from any patch of crimgrass, and has nearly gravity-defying rigidity; allowing the plant to grow up to six feet in any direction. It often grows in a mazelike pattern, though breaking it is surprisingly easy and its remains don't cause The Crimson to spread further.
However, beware being too close to crimthorn, as it is hard enough to pierce armor, though that may account for how brittle it is. Crimthorn does not produce crimson spores, and has to touch other plants or terrain directly in order to spread the condition.