pictures please

Most likely rootstock. Pics would sure confirm.

probably a watersprout, not a vine

The lemon tree is a dwarf & was breed this way for low Temps, it gets from 15 to 115 here the high desert.

all that twisty viny think needs to be remove ASAP. It is flying dragon rootstock and it take over your tree if you leave it to grow. It is the BEST rootstock for growing tasty fruit on the grafted cultivar (Lemon) tree.

I have a Fukushu kumquat tree on flying dragon.

It will stay small and compact.

Now I know what Flying Dragon Rootstock looks like when it grows.

Thomas Manning, all that twisty stuff is the rootstock trying to take over. It must be removed as close to the trunk as possible, or it will out-compete your lemon. It is Poncirus trifoliata 'Flying Dragon' and is a commonly used rootstock that contributes a dwarfing effect to the edible variety, as well as cold tolerance, to some degree.

Thank you, its growing out of the tree & its why I didn't remove it, flying dragon they add it so it dwarfs effect & gives the plant able to durvive in cold weather temps.

I should of asked last year, I'm going to remove it now, Thank you everyone as I didn't plant it in the ground & soil is weak no nutrients & it snows here. I put the tree close to my house when it gets cold & no watering. I had a avocado that could go 12 temp, my luck we went down to 9 & lost them. It was grafted in the middle & I swear it said pinnable, orange & lemon. I would of got more lemons then one you see in Pic. I grow orchids & San marzano tomatoes from my home Italy. P.s. I removed the flying dragon great to keep pets away & burglar.