Regina's Apple Tree

Regina's Apple Tree, which she claims grows honey crisp apples, has been under her care in both Fairytale Land and Storybrooke. She has had it since she was a young girl and boasts of the tree's heartiness. Regina tends the tree with care, and is frequently seen having conversations near it. It is first featured in "Pilot".

History
Regina is seen tending her apple tree when Sidney Glass brings her a copy of the latest edition of The Daily Mirror, which shows an arrest photo of Emma Swan. Regina later goes to find Emma and offers her some apples, explaining that she picked them from her honey crisp tree and provides some background history on the tree. Henry Mills later warns Emma not to eat apples from Regina's tree, taking the apple from her hand and throwing it. ("Pilot")

Emma takes a chainsaw to the tree after getting frustrated with Regina's scheming ways in getting her arrested. Regina sees her through the window and comes out, demanding to know what Emma is doing to her tree. After arresting Emma at the mayor's urging, Sheriff Graham goes to talk to Regina and, once again, finds her in the yard tending her damaged tree. ("The Thing You Love Most")

Back in Fairytale Land, a much younger Queen Regina is living at the palace with King Leopold when he returns one day with the Genie. After finding her by her apple tree, the Genie has an emotional discussion with Regina, who manipulates him into killing the king. The Genie is later shown under Regina's apple tree, getting the box from Regina's father that contained the viper to kill the king. ("Fruit of the Poisonous Tree")

Regina has a nightmare in which the townspeople remember their lives from Fairytale Land, and seek her out for vengeance. They tie to her apple tree in the town center, with the purified apples so rotten that they turn into a black ooze when squished in Emma's hand. After Regina wakes from this nightmare, she notices that her apple tree is actually rotting and confronts Mr. Gold about it being a sign that the curse is breaking. ("An Apple Red as Blood")

Regina's apple tree gets rejuvenated after she gets her mother's old book of spells to reclaim her magic powers. She opens the book, and inhales the magical vapors that disperse into the air. ("We Are Both")

Trivia

 * Goof: In "The Thing You Love Most", Regina claims to Emma that her apples are from a Honeycrisp tree. However, the apples in the basket, on the tree and everywhere else that apples are used in the set dressing are Red Delicious, which have a totally different shape and color from Honeycrisp apples. Honeycrisp apples were not commercially available until 1991, and must be specifically bred.
 * The episode title "Fruit of the Poisonous Tree" alludes to the scenes taking place under the tree during which Regina, the Genie and her father plot to kill King Leopold.
 * The apple tree appears to be symbolically tied to either the power of the Dark Curse or to Regina's magic - the last of which she used to bring her poisoned apple back from Fairytale Land.
 * The poisoned apple that Regina uses for the sleeping curse may have originally come from her apple tree when it was in Fairytale Land.