Demontrumpets, as illuded to by the name, are not normal plants, but are plants who hold their origin in the Abyss. Perhaps brought by summoned demons, perhaps created by a dark god for some purpose, perhaps simple plants mutated by an artifact of great evil.
A large, ruby-red pepper, found in dry regions; much prized by alchemists and gourmands alike.
If a creature is transformed into another creature (say, a human into a dog), then that creature will become more and more accustomed to the new form until a point is reached where reversing the spell is impossible. A second transformation is possible, but the creature will have to go through the whole process again.