Mind your own business!

(Soleirolia soleirolii )

It's so long since I used cash I'm not sure if that's a 5 or 10p!

Soleirolia soleirolii - known as 'baby tears' here but typically forms a dense mat.

Thanks, ladies.

That was my opinion, as well. but I'd only ever seen it growing out of old cracks and forming dense mats, as in the pic.

I wonder how it got there. I haven't seen any locally. It's apparent loci would be consistant with having been in with the medium it came in, but can it propagate from bits of roots after 3-4 years? Can't see that.

The tiniest bit will root. Might have come via untidy birds or on footwear after you've been to one of those lovely Cornish gardens.

"The tiniest bit will root."

No kidding!! There was a large, lush colony of it growing in coarse gravel beneath the racks that held groundcovers at the nursery where I used to work. It grew just from random bits and bobs that broke off from handling of the potted GC's.