Ah, right, the second photo just appeared ... did you find it on the ground? I think it might be an old walnut from a previous year ......... or a diseased one from this year. It's hard to tell without handling it. It could even be some sort of gall or oak apple or similar.
Looks a bit like a walnut ... but they usually have a raised rim around the edges of the two halves... crack it open and let's have a look inside ...
Was it on a tree or on the ground ... any chance of a photo of the tree leaves?
Panic not They're caused by the Walnut Gall Mite ... they won't harm your tree. More info here
I've found some others ... a bit swamped by a salvia and some rudbeckias (the garden did get away from me a bit this summer )... they're much more like the ones on the seed packet ... think the one in the photo I posted must've been an odd stray seed ... fascinating ... I must keep an eye on it.
Cherry plums ... make great jam.
I'll keep an eye on it ... haven't seen any bees on it yet ... but to be fair it's been in the shade up until a few minutes ago, and the wind's blowing a hooley here now ... haven't seen many bees in the front garden this morning, but lots on my runner beans earlier on
I'll have a look for more next time I go out there ........
Josiecube that does look more like 'my Mondarda' than the pic on the seed packet that I have from Sarah Raven ...
If I can find any more that have survived we may know whether it's a random wrong seed or the whole packet full.
That's what happened to mine a few years ago ... first the spuds got it then the tomatoes. I don't grow spuds any more ... that way the tomatoes are a bit safer.
Dig them up and get what crop you can.