The Bubotuber is a magical plant full of stinky pus. Bubotuber pus is used for healing potions (GF13). A bubotuber looks like a thick, black, giant slug (it even squirms slightly, although it sticks vertically out of the soil) with many large shiny swellings on it that are filled with a yellow-green pus that smells like petrol (GF13).
As Professor Sprout taught her fourth-year students, the pus reacts oddly with human skin. Undiluted, it will raise horribly painful boils on contact (GF28), but properly diluted and processed can be used to cure acne (GF13). The pimple-curing properties were discovered by Sacharissa Tugwood (FW). (Also JKR -W1).
During the Tri-Wizard Tournament, after journalist Rita Skeeter wrote that Harry and Hermione were in a love triangle with Viktor Krum, Hermione received an envelope full of undiluted bubotuber pus that made her hands swell up. (GF14)
Bubotuber is used for potions that heal acne.
From the Medieval Latin būbō for "swelling pustule," and "tuber" meaning "fleshy root" from Latin "tumere" = "to swell"
bubo = (Gr. boubôn, "groin") (plural form: buboes) is a swelling of the lymph nodes. It is found in infections such as bubonic plague. It is similar in appearance to a huge blister, and usually appears under the armpit, in the groin or on the neck. Tuber = In anatomy, the term tubercle may describe a round lump or warty outgrowth found on bones or skin, or, in cases of tuberculosis, in the lungs (Wikipedia). A tuber is also the root that is characteristically enlarged in tuberous plants such a potatoes and yams.
It's quite humorous that a plant that releases pus when it's pimple-like swellings are squeezed is used in acne potions.