The Mimbulus mimbletonia is an extremely rare magical plant. It is described as looking like a small, grey cactus but is covered with pulsating boils instead of spines. Its unsettling appearance is noted by Harry Potter to resemble a “diseased internal organ”. The plant is known to make small twitching movements and crooning noises, particularly when it is content or being tended to.
The primary and most dramatic characteristic of the Mimbulus mimbletonia is its unique defense mechanism. When it feels threatened or is prodded, it violently squirts a large quantity of a substance known as Stinksap from its boils. Stinksap is a non-poisonous, thick, dark greenish liquid that smells powerfully of “rancid manure”. While harmless, the fluid is extremely unpleasant and difficult to remove. This defensive trait makes the plant a curiosity, though not one suited for casual handling without caution. Despite its bizarre properties, the plant is of great interest to Herbologists. Professor Sprout, the Herbology teacher at Hogwarts, was highly impressed with Neville Longbottom's specimen.
Neville Longbottom received a Mimbulus mimbletonia for his fifteenth birthday in the summer of 1995 from his Great Uncle Algie, who had procured it in Assyria. Neville was immensely proud of the plant, as it was very rare and of significant interest to Herbology experts. Later that same year, the name of the plant was used as a password for the Gryffindor Tower. The Fat Lady, the portrait guarding the entrance, found the name particularly difficult to remember.
The Mimbulus mimbletonia makes its most notable appearance at the beginning of Harry Potter and the Order of the Phoenix. Aboard the Hogwarts Express, Neville Longbottom proudly shows his new plant to Harry Potter, Ginny Weasley, and Luna Lovegood. When Harry prods the plant at Luna's suggestion, it sprays the entire compartment and its occupants with Stinksap. This event serves as the initial introduction of Luna Lovegood to Harry and his friends, highlighting her quirky and curious nature. Later in the school year, Neville's proficiency with the plant earns him twenty House Points for Gryffindor from Professor Sprout, providing a rare moment of academic recognition and confidence for him.