#poncirus is a common rootstock for other citruses

“Or, if you need a barrier planting to keep out dogs, burglars or college students averse to staying on the walks, it can be made into a hedge.  A number of 3-foot tall, impenetrable hedges have been grown for over 50 years at Oklahoma State University in Stillwater.  The hedges are so dense they can be walked on.  Though deciduous, the green thorns are thick enough they look evergreen in winter.”

—Plant of the Week: Trifoliate Orange (Hardy Orange), University of Arkansas Cooperative Extension Service