Refere-se sem ambiguidade à madeira.
So Death crossed to an elder tree on the banks of the river, fashioned a wand from a branch that hung there, and gave it to the oldest brother.
E:
“Nah, that story’s just one of those things you tell kids to teach them lessons, isn’t it? ‘Don’t go looking for trouble, don’t pick fights, don’t go messing around with stuff that’s best left alone! Just keep your head down, mind your own business, and you’ll be okay’ Come to think of it,” Ron added, “maybe that story’s why elder wands are supposed to be unlucky.”
“What are you talking about?”
“One of those superstitions, isn’t it? ‘May-born witches will marry Muggles.’ ‘Jinx by twilight, undone by midnight.’ ‘Wand of elder, never prosper.’ You must’ve heard them. My mum’s full of them.”