Are you sure you weren't picking mint? My experience with mint is that it takes over, crowding everything around it out. That's why I rarely grow it anymore, and when I do, only in pots. If I were you, I'd be tempted to dig the mint up and pot it to keep it from taking over. On the other hand, who knows what could have happened if they both dumped seeds in the same place? By the way, how does it taste? I always find oregano too intense or pungent. Have you ever grown Cuban oregano? It's very attractive and much milder.

I'd be surprised if the mint had spread over there, since it's in a raised, rock-coverd mound, but anything's possible with mints!  I'm also pretty sure the leaves I picked were my oregano, from the way they looked and the fact that they were springing up among the dry, brown stems from lasts summer's oregano. 

I don't know what kind of oregano I have-- it was actually some I dug up from  my mom's oregano patch, but it's fantastic for Italian cooking and salad dressings.  At least is was...  I'm hoping not all the leaves I harvest from my oregano patch will taste like mint.

That is very weird......any possibility that the oregano touched the mint leaves????? Maybe that's how they acquired the flavor.

The last time I planted mint in the corner of my garden, it was so impossible to contain that I spent more time digging it up to get rid of it than I did doing anything else.

Do either your mint or your oregano ever go to seed? I'm wondering whether if your plants went to seed and the seeds dropped on the ground (as is often the case,) that the plant that sprouted as a result of the dropped seeds is a hybrid. Would that explain it, at least somewhat logically?

Hybridization is usually do to cross polination...  if there was cross polination, then yeah, that makes sense!  I know the oregano has gone to seed.  I guess the mint did too...  there's not as much of it, so I don't really recall. 

I just hope the rest of my oregano doesn't taste like mint!  I really did love harvesting that oregano...