Gillyweed

Gillyweed is a magical plant that, when eaten, allows a witch or wizard to breathe underwater. It is said to resemble a bundle of slimy, grey-green rat tails. When it is eaten, it gives the consumer fish-like properties, such as gills and webbing between the fingers and toes, allowing one to process oxygen from water and to swim underwater with ease. It is native to the Mediterranean Sea.

History
Gillyweed was first discovered by Herbologist Beaumont Majoribanks some time before 1845. However, the magical properties of Gillyweed remained unknown until Elladora Ketteridge ate the plant and nearly suffocated, recovering only when she stuck her head into a bucket of water.

Harry Potter used Gillyweed during the Second Task of the 1994 Triwizard Tournament. Dobby gave it to him, after overhearing a conversation which Barty Crouch Jr, disguised as Alastor Moody, staged with Professor McGonagall.

Effects
When Gillyweed is eaten by a witch or wizard, it gives them fish-like properties, including gills to process oxygen from water, webbing between the fingers and toes for easier swimming, preventing blinking, and adapting to cold temperatures in water. While under the effects of Gillyweed, one cannot breathe air with their lungs. There is some debate among Herbologists as to the duration of the effects of Gillyweed in fresh water versus salt water, but a sprig of Gillyweed in fresh water lasts for about an hour.

Connection with Gillywater
Gillyweed can also presumably be used as an ingredient in a drink called Gillywater. Professor McGonagall once ordered a glass of it in The Three Broomsticks. Romilda Vane offered Harry a glass of Gillywater spiked with a Love Potion, in an attempt to get Harry to ask her to Professor Slughorn's Christmas Party.

Behind the scenes

 * Chocolate Frog Cards state that Majoribanks discovered Gillyweed in the mid-eighteenth or nineteenth century, while Elladora Ketteridge is said to have discovered its effects about a century earlier. This discrepancy is likely just an error, as the issue would be fixed if Majoribanks was alive during the same time as, or before Ketteridge, as he merely discovered the existence of Gillyweed, while Ketteridge discovered its magical effects.
 * In the video game, the Gillyweed allows Harry to breathe underwater and webs his toes. However, Harry does not have gills, nor are his fingers webbed, presumably for graphical limitations.
 * Gillyweed is featured in Magical Water Plants of the Mediterranean and Magical Water Plants of the Highland Lochs, books lent to Neville Longbottom by Barty Crouch Jr, who was posing as Alastor Moody.
 * In the film, Neville Longbottom tells Harry about Gillyweed (he learned of it in a book Moody had given him), and Harry is given the actual Gillyweed by Neville and told to put it in his mouth by Crouch/Moody.
 * In the book, it is Dobby who tells Harry about it and gives Harry the Gillyweed, after overhearing Moody/Barty's staged conversation with Professor McGonagall about which tactic the Champions might use in the Second Task.
 * There seems to be some Gillyweed stored in the Herbology Greenhouses as well as Professor Snape's private potion stores. This suggests that Gillyweed can also been used as an ingredient in at least one potion, instead of being eaten raw.
 * Gillyweed's properties along with it being indigenous to the Mediterranean might allude to a Greek myth of a mortal who ingested an herb that rendered him aquatic for the rest of his life who went on to become a minor sea god.

Appearances

 * PS G

Notes and references
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