Let's just be thankful that the Cactuar exists strictly in the world of fantasy
whether or not there really is such a thing as a "walking cactus" or "Spanish dagger," as mentioned in the movie. At the time, I was able to find:
1. A prehistoric arthropod discovered in China, a species of Diania dubbed "walking cactus"
2. Two species of yucca called "Spanish dagger." Yucca gloriosa, which is not native to the Mojave desert (which I discovered in researching the article), and Yucca schidigera which is native to the Mojave (which a commenter later turned up).
3. A true cactus, Stenocereus eruca, known as the "walking cactus" or "creeping devil," capable of moving across the desert floor at a blistering top speed of two feet per year.
But in the months since that article was posted, another commenter pointed out a fourth walking cactus. And like the walking cactus in Rango, these ones move like humans, talk and hatch evil schemes. It is none other than the Cactuar of the Final Fantasy video game franchise.
The Cactuar's original design stems from a doodle in the high school notebooks of Final Fantasy character designer Tetsuya Nomura. They are a recurring enemy in the series, and take the form of the familiar barrel cactus with two legs and two arms which move stiffly, usually held at right angles. The Cactuar have two eyes and a mouth, usually depicted as two big black holes for the eyes and one long black hole for the mouth. In some versions the Cactaur is also known as Cactrots or as Sabotenders.
Like many Final Fantasy characters, the Cactuar appears in several Mario games as well: in Mario Hoops 3-On-3 it can be unlocked as a playable character on the Glare Desert level. Other Cactuars appear in the Glare Desert as spectators and in the final cut scene. The basketball-playing variety of Cactuar has actual segmented legs and arms, which allows him to run, jump, and dunk the ball. Cactuar can also play volleyball in Mario Sports Mix.
As a general rule, Cactuars have low HP, but they move quickly. They also have a very effective trademark attack: "1,000 Needles," which deals 1,000 HP damage regardless of your defenses. Let's just be thankful that the Cactuar exists strictly in the world of fantasy, because encountering an attack like that is a rather shocking thought!