@ofm, Okay, here ya go. I do think the leaves are the best way to distinguish these however.
Here is that oxalis we talked about:
Very fine roots are clumped in soil and water as I tried to rinse off enough soil to show but all I got was this....
Here is Clover root system:
Looking closely I can see how different they are but I don't think the photo shows it all that well. Also, in the yard the clover grows very densely matted so it was hard to find a good single clump to show. And these leaves are not as distinct either ....
Here is clover again, roots closeup with the nodules that are the nitrogen fixing thingies (notice the botanical technical term here
):
I believe those little white lumps are where the plant has collected nitrogen from the atmosphere and stores it.... ??
Here is a picture of both plants side by side:
Hope this helps!