Thistle as a thistle

"It's finally done?" Dean was impatient as always.
"Almost, pas me the Carduus acanthoides." Dean threw on him the requested plant.
Sam's hand stopped at last moment "Dean for love of Chuck if you don't want to help then leave."
"What did I do this time?"
"This is not Carduus acanthoides this is Carduus crispus. You could have ruined our chance to make the spell of protection for Cas. You know I'm not good at this magic shits, so please go grab some beer and let me work in peace."
Dean was leaving the room murmuring. "Thistle as a thistle."