Mullein

The name Aaron’s Beard is applied to several plants; so is Aaron’s Rod, the latter name being perhaps most commonly given to the mullein, Verbascum Thapsus, because of its long, straight stem.

There be foure ſortes of Mulleyne, as [Pedanius] Dioſcorides writeth: wherof yͤ two firſt are white Mulleyne, and of them one is Male, and the other female: The third is blacke Mulleyne: The fourth is wilde Mulleyne. […] The white male Mulleyn (or rather Wolleyn) hath […] the whole top with his pleaſant yellow floures ſheweth like to a waxe Candell or taper cunningly wrought.

As we all know, witches ride through the air on a broom, but sometimes their means of locomotion was a bulrush, a branch of thorn, mullein stalks, cornstalk, or ragweed, called fairies' horse in Ireland.