Two breeds of roses on same plant??

[FirenzeArno]

A few months ago I rescued a rose tree from a clearance bin in The Range. It had a bare trunk with one stem at the top with 3 leaves on it. About 3 feet tall. DP laughed at its sorry state but we planted it anyway.

A few months later now and it has come on beautifully and has filled out with lots of droopy (but healthy!) stems with tiny dark green waxy looking leaves and blossomed with little pink roses. It started to look like a weeping rose tree (if that's a thing!)

However over the past few weeks another stem has started to grow off the main trunk and grow straight upwards. This stem has different leaves. They are much larger, rough to touch. Much like the leaves on a bunch of shop bought roses. This stem hasn't flowered, has large thorns on it and grows about an inch - 2 inches every week so the overall tree is about 6 foot tall now and keeps going.

Anyone know why this plant looks to have two completely different breeds of plant growing out of it? Should I remove the large straight up stem?

Thanks!

I think (non expert here) that roses are often grafted onto a different root stock. What's coming through is the rose from the rootstock. At least I think that's what has happened.

One of the stems is the rootstock, which is often something similar to a briar rose. I'm not quite sure from your description which is which though! Do you have any photos?

Agree, it's a sucker from the rootstock its grafted on, which needs to be removed by tugging it cleanly off the base (not cut).