Succulents (6)
(Another definition for agaves that I've seen is " Spiky plants".)
'succulents' is the definition.
(cactus is a kind of succulent)
This is all the clue.
(Other definitions for cacti that I've seen before include "Desert features" , "They store water" , "Spiny succulent plants" , "Prickly plants" , "Spiky plants found in deserts" .)