Sorrel can take over anyone's garden, and a characteristic of it is you can't generally pull out the whole root system. For some reason, this one came up whole and it's fascinating. The plants look like Oxalis violacea - pinkish flowers - but who knows. There are about 800 Oxalis types.
The tap root was damp and completely translucent. It didn't seem uneven enough to be a nitrogen-fixing nodule that had grown over the root, and I can't find anything like it on the web. You can see the bulblets around the top of the tap root. These bulblets stay in the soil after the main plant dies back and each one grows a new plant. The seeds are also explosive and shoot several inches, so one flower can reseed a whole area. Many Oxalis can also form rhizomes that run along horizontally, but this one hadn't (yet).
My iguanas eat the leaves occasionally - even after I've carefully explained to them that sorrel is high in oxalic acid, which is a minor annoyance to humans but can be a danger to iguanas. "Sorrel" means sour, and the sourness comes from the oxalic acid. That's the same sourness that's in rhubarb - and for that matter, the one that's in the generally-regarded-as-poisonous Dieffenbachia, Dumb Cane.
I've put a larger picture of it here.