A cactus was a type of plant, found on several planets, including Earth.
In recalling his late 19th century history of the Ancient West, Pavel Chekov noted that "all western cossacks had were poisonous snakes and cactus plants." (TOS: "Spectre of the Gun")
Vina believed that all of Mojave was once covered with cactus and blowing sand. (TOS: "The Cage")
Ard'rian McKenzie kept several cacti in her home on Tau Cygna V. (TNG: "The Ensigns of Command")
Yalasat, a dish popular amongst Zobral's clan, was made from a cactus native to the Northern Foothills of their planet. (ENT: "Desert Crossing")
A variety of cactus known as Cyprion cactus was aboard the USS Enterprise-D arboretum. (TNG: "Genesis")