OED pergola: an archway in a garden or park consisting of a framework covered with trained climbing or trailing plants.
Does 'trained' here means that the plant has been 'trained' to grow in a specific path? If so, I didn't know trained could be applied to anything besides people or animals.
Naturally, "train" means something slightly different for plants, because you have to physically force them to do something, rather than persuading them to. Also, plants tend not to remember what they've been trained to do.