Mexican agave plant whose large fleshy leaves yield a fibre used for rope making (5)
I believe the answer is:
sisal
(Other definitions for sisal that I've seen before include "Plant fibre used for making rope" , "Rope-fibre made from leaves of tropical plant" , "Plant fibre used to make string" , "Agave cultivated for its fibre" , "Fibrous plant used for rope" .)