Is the stem red and fuzzy? If it is, could be German Raspberry, Wineberry, lots of other names. Could you post a pic of the stem?

Looks like a Ribes to me, quite possibly a blackcurrant. They grow very easily from cuttings and even a pruned twig left on the ground can grow roots. The other possibilities are a seedling from a fallen berry or a sprout from a bit of root you didn't get out. Anyhow, it is too close to the Gooseberry, so if you want to keep it it will need moving.

Thank you both for your comments. The is a close-up of the stem, which is indeed reddish. It's not prickly, but yes, sort of fuzzy. The other thing about this mystery plant is that is was very, very late dropping its leaves last fall. We didn't have any snow or very cold weather this past winter, and it seemed like it was going to keep its leaves forever (unlike the gooseberries and the black currents).

Yes, I agree it's too close to the gooseberry, and sadly I don't have any place to transplant it so I guess I'll never see it develop any fruit...

Ribes still fits. What do the leaves smell like when you scrunch one up? If it's Tom cat you have a black currant. If not it could be a red currant.

A young plant could well hold its leaves longer than more mature ones. Even on older bushes the growing tips are last to lose their leaves.

The leaves on the mystery plant don't smell. But then neither do the leaves on my Crandall black currant (which is not really a regular black currant (Ribes nigrum), but rather Ribes odoratum). Here's another picture of yet another volunteer mystery plant (the fourth!) I found today right next to a Friend (Ukrainian thornless) gooseberry. I'll post another follow-up picture of a volunteer Crandall black currant that I also found today (in another part of the yard) so you can see how much more finely dissected the leaves are on the Crandall compared to the mystery plant. Obviously I've got to pull these volunteers out now that I see they are popping up way too tightly.

Just for comparison, here's a brand new volunteer Crandall black currant in another part of the yard (it came up about 20 inches away from the main stool). The mystery plant has much bigger, less crinkly, somewhat darker colored leaves.

Yes, this is black currant, the first one looks like raspberry.

Konrad, Crandall - as margi1533 says - is R odoratum. The black currant I am referring to is not Crandall but R nigrum. If the leaves don't pong it's not R nigrum. That leaves Red Currant, R rubrum, as a possible candidate. It's interesting that you are finding more volunteers. The second one could almost be a Gooseberry itself.

Can you leave them long enough to see the flowers?

I can't say I think either of the volunteers looks at all like a raspberry. They have single palmate leaves (Ribes), not palmately compound (Rubus).

Thanks for continuing to try to help me solve this mystery!

Konrad, the last picture is indeed a Crandall black currant, popping up not far from its parent. About 3 years ago I had two of these plants planted at the base of the low stone wall you can barely make out in the first (top of this thread) picture. I took them out and moved them to a different place in my yard where they would have more space. So it's possible that a little piece of root left behind grew up through the dirt (our neighborhood is very hilly - both north-south and east-west, so ground elevations change constantly in all directions) ... except that these volunteers look so different from both the gooseberries that they're next to, as well as the Crandall. The biggest difference is the size and appearance of the leaves.

Flora, I would LOVE to let these volunteers keep growing (which is why I didn't pull the two biggest ones last year when I first spotted them), but I'm worried about crowding the gooseberries. They (the volunteers) didn't flower at all last year (no surprise, given their age). If they are, in fact, red currants, that's a mystery too because nobody around us grows any type of currants (except for my Crandalls). I guess it's very possible that birds came to eat the gooseberries and in the process deposited seeds while they were busy eating (nature's input and output!). But again, seeds of what???

The Pacific Northwest is prime berry country, (and I do have raspberries and blackberries in a different part of the yard). But these mystery plants look like nothing else in my yard.