Mentha × piperita

…, I am not exactly sure where I got this plant from as it was growing at home in one of the pots as an uninvited guest. I clicked it before I left for the trip and when I got back, my mother had emptied the pot for another set of plants so I couldn’t take a closer look.
The links you have provided look spot on for Mentha x piperita! But how is it different from the one in the last link?

Thanks sir.
Fits with Mentha spicata– leaves petiolate, calyx teeth triangular, corolla purplish as opposed to leaves subsessile, calyx teeth linear and corolla white with red tinge on the lobes in Mentha x piperita. Please validate.

I am none to validate any id. Instead, I write what I think.

First, let me check if a hybrid can produce seeds, and if those seeds can be fertile. FoP says Mentha x piperita L. is sterile. PFAF informs M. x p. vulgaris L. is a natural hybrid and do propagate by seeds. I cannot say if two taxa, M. x p. & M. x p. v. are same or not.

My 2nd Q. is if a hybrid can have characters of one or both of its parents. I think yes.

I will check probability of this species to be Mentha x piperita L. –

1. stem branched purple-red (FoC) = pic4
2. petiole length won’t help = check two taxa both in FoP and in FoC. Even then spicata is sessile to sub-sessile
3. petiole purple = pic4
4. bracts linear-lanceolate (FoC) = pic6, below the first flower-bud right to axis
5. calyx tinged purple = pic1,6,7
6. calyx teeth = my view, based on recent Leucas spp., features like ‘triangular’, ‘subulate’ etc are very debatable
7. corolla colour = not very important when it comes to cultivated spp., however, can be lilac