I remember as a adolescent being somewhat fascinated by the power of tanna leaves in those old Universal mummy movies. Ardath Bey would burn a few and chant some lines to direct the mummy to life to find his lost love Princess Ankh-es-en-amon. WOW, the power of plants. Well, it turns out that there are a lot of fake plants used in fiction.
Plants from J. K. Rowling's Harry Potter series
Abyssinian shrivelfig: When peeled, shrivelfigs are used as an ingredient in Shrinking Solution.
Alihotsy: ingestion of its leaves causes hysteria.
Bouncing bulb: an animated bulb plant; appears in Harry Potter and the Goblet of Fire.
Bubotuber: thick, black, slug-like plants that grow vertically out of the soil. It is normal for them to squirm and they are covered in pus-filled swellings.
Devil's Snare: a vine plant that strangles people and wilts in the sunlight. Harry, Ron, and Hermione find themselves caught in it in Harry Potter and the Sorcerer's Stone, and it strangles a man in St. Mungo's hospital in Harry Potter and the Order of the Phoenix.
Dittany: a plant which has the ability to cure wounds.
Fanged Geranium: a geranium that bites humans.
Flitterbloom: a plant that superficially resembles a Devil's Snare but is non-violent.
Flutterby bush: a bush that quivers and shakes.
Gillyweed: when eaten, this plant causes the user to grow gills and webbed feet and fingers, thus become able to breathe and swim underwater, for approximately an hour, depending on whether the user is surrounded by fresh or salt water.
Gurdyroot: resembles a green onion.
Mandrakes: tubers that look like babies when young. Their screams can kill when fully grown. A potion made from mature mandrakes can restore victims that have been Petrified. A different kind of Mandrake is a real plant. Whilst the Mandrake as it appears in the books and films is fictional, Rowling's description does reflect genuinely held beliefs about the Mandrake, in particular, the danger surrounding its screams. This lead to the practice of using dogs to collect the mandrake, and the blocking of ears during collecting.
Mimbulus mimbletonia: a cactus with boils instead of spines; sprays foul-smelling goo in a large radius when poked.
Puffapod: a large pink pod filled with seeds; bursts into flower when dropped.
Screechsnap: a semi-sentient plant that wriggles and squeaks uncomfortably when given too much dragon dung manure.
Snargaluff: a dangerous man-eating carnivorous plant, deceptively taking shape of a dead tree stump when in passive condition; shoots out thorny vines to catch the prey. From Harry Potter and the Half-Blood Prince.
Venomous Tentacula: a species of magical plant that possess a series of dark red spiny tentacles; appears in PC video games as a Venus Flytrap with a tentacled base, later rendered like a flower with teeth inside the petals. A wizard comedian is known to have survived eating this plant on a bet, though he is still purple.
Whomping Willow: a large, violent tree that thrashes its branches at those who approach it. Though it first appears in Harry Potter and the Chamber of Secrets, it features significantly in Harry Potter and the Prisoner of Azkaban.
Note that dittany and mandrakes exist in reality, though are not credited with the powers they are supposed to have in the wizarding world.
For many more...
List of fictional plants [Wikipedia]