Elm

A wand wood (Pm).

• Elm wands are sophisticated and capable of advanced magic. They also produce the "fewest accidents" and the "most elegant charms and spells"  (Pm).
• Although purebloods prefer elm wands, Mr. Ollivander states that he has sold some to Muggleborns (Pm).
• Lucius Malfoy's elm wand with dragon heartstring was taken from him by Lord Voldemort (DH1), and later destroyed by Harry Potter during the Battle of the Seven Potters when Harry's wand turned of its own accord and blasted the wand as Voldemort held it (DH4,DH5,DH35).

Voldemort was assured by Mr. Ollivander that if he used a different  wand against Harry then there would be no repeat of the Priori Incantatum effect as in the Riddle graveyard from the twin phoenix feather wand cores (DH5, DH24). So the Dark Lord was furious that Harry's wand destroyed the elm wand anyway. Dumbledore explained in "King's Cross" that Harry's holly-phoenix wand had absorbed some of the Dark Lord's essence in the graveyard and saw him as a threat, so Lucius's wand or wand core had nothing to do with the way Harry's wand reacted during the Battle of the Seven Potters:

"So your wand recognized him when he pursued you, recognized a man who was both kin and mortal enemy, and it regurgitated some of his own magic against him, magic much more powerful than anything Lucius’s wand had ever performed. Your wand now contained the power of your enormous courage and of Voldemort’s own deadly skill: What chance did that poor stick of Lucius Malfoy’s stand?”(DH35)