Yes, seeds. Those Oxalis are prolific seeders, with popping pods and root structures to hide with while the above-ground parts are attacked. Nasty!
It is raining often recently, which I am very happy about. I started my spring seeds and will be redoing some of the rock garden later. I knew it was not a good idea to plant the fuzzy Cerastium in such a small-scale planting, but I still did it. There are babies coming up in other places already, but I will just harvest them and hope it doesn't become too much a problem later on. I'll probably just dig it up and replant it in a sunken pot.