Rubus species or hybrid. ie a bramble or blackberry. Is the last picture definitely the same plant?

I think the last picture is just a little blurry and it's the same plant, some kind of creeping blackberry. If you're on the eat coast it's likely Northern dewberry

clipping anything is called pruning.. NOTHING DIES FROM PRUNING ALONE...

you must apply a stump killer after you make the cut.;. i used to use roundup ...undiluted...

a handy applicator like this is hard to lose.. precise with minimal application... and must be stored away from the hot dogs ...

try the NAME THAT PLANT forum next time...

ken

https://duckduckgo.com/?q=plochman+yellow+mustard&t=ffsb&iar=images&iax=images&ia=images

"NOTHING DIES FROM PRUNING ALONE"

Well, Rubus certainly won't but plenty of plants will die if cut down at the base. Using that sweeping generalisation to make gardening decisions could lead to trouble.

LEAVE ABOUT 12 INCHES OF THE VINE THAT STICKS OUT THE GROUND. SCRAPE OFF ABOUT 2 INCHES OFF THE SKIN OF THE VINE. NOW PLACE. THE SKINNED VINE INTO A SMALL BOTTLE OF WEED KILLER. NOW BRACE THE BOTTLE SO IT DOSEN'T FALL OVER. THIS WILL KILL THE BULB BELOW THE GROUND. YOU CAN ORDER OR BUY AT A FLORIST THE SMALL PLATIC BOTTLES THAT USE TO KEEP THEIR SOLD FLOWERS FRESH. HERE IN FLORIDA, WE HAVE A BIG PROBLEM WITH THE THRONNEY VINES.