Robert Chambers wrote in news:HQwrd.1401
:

I'm sorry to have not included a description then. There's no need to
sully yourself by watching an HP flick. for the purposes of this
discussion it's a tree that for one reason or another is very bad
tempered and if you get near it, it's likely to reach over and "whomp"
you with a vengeance. It smashed up a Ford Anglia once and the latest
movie it flings the people around.

I think it's make believe though so I don't think you can order them
from your usual suppliers.

You can grow your own "whomping willow". All you need is Harry Potter's
Chamber Pot of Secrets. The fertilizer is the key.