Corn stalks
Corn-on-the-cob, offered by Aunt Adah
A sack of corn, in front of the Tombstone general store
Corn was a plant indigenous to Earth. It was a grain used by Humans as food.
Corn kernels, when taken off the cob and dried, were cooked in oil to make popcorn, which was often served at movie showings. (ENT: "Dear Doctor"; VOY: "Repression")
According to her guidebook, Shannon O'Donnel was near a re-creation of The Last Supper made entirely of corn when she was driving through Indiana in 2000. (VOY: "11:59")
In 2151, a Klingon K'toch-class scoutship crash-landed in a cornfield in Broken Bow, Oklahoma. The field belonged to a corn farmer named Moore, who subsequently shot the pilot of the craft, a Klingon named Klaang, after the Klingon destroyed his silo. (ENT: "Broken Bow")
In 2259, Leonard McCoy asked James T. Kirk "Are you out of your corn-fed mind?" when he wanted to open up one of the specialized torpedoes on the USS Enterprise on the advice of John Harrison. (Star Trek Into Darkness)
In 2268, a sack of corn was one of the items created by the Melkotians as part of their re-creation of Tombstone, Arizona. (TOS: "Spectre of the Gun")
In 2371, when the USS Voyager was pulled into the Delta Quadrant by the Caretaker and transported aboard the Caretaker's array into a holographic simulation of a farmyard, the crew walked past a garden patch of corn stalks. One of the holograms, Aunt Adah, offered the crewmembers some corn-on-the-cob, lemonade, and sugar cookies. (VOY: "Caretaker")
Three years later, aboard Voyager, Tom Paris noted that a mystery meal prepared by Neelix tasted "vaguely like chicken, but it has the consistency of corn husks." (VOY: "Hunters")
In 2380 and 2381, Ensign Jet Manhaver enjoyed eating "delicious street corn", but occasionally a stray kernel would fall on his uniform collar, making it appear that he was a lieutenant. (LD: "Cupid's Errant Arrow", "Kayshon, His Eyes Open")