This is my neighbors plant, so all info is hearsay. She never saw blooms, but says it had round, yellow fruits, and grew up and over an 8' block wall. when I asked about sap, she said no, but he said white sap.
This a cutting that has been in the ground about 4 months. Thorns are about 4" long.
SOLVED: I'm thinking euphorbia
I'm pretty sure it is an Opuntia/Cylindropuntia/Austrocylindropuntia. One of those. The real leaves of Opuntia are showing in your plant which fall off.
I'll look through those, but leave it open for now. Thanks, growin.
Most likely Austrocylindropuntia subulata