Both thorns and new stems emerge from dark, papery buds - here you can see these sheaths before they are shed. If you look closely at the top one, you can see the tip of the sharp, new thorn emerging. The roots are as stiff and inflexible as the stems. This is only part of one mass that I dug up. The green stems, either angled or rounded, are what you see above ground as small clumps or massive thickets .
Older stems become discolored, sort of a dark grayish-brown.
The whitish colored stem is typical of the underground portions, which are actually rhizomes. Any parts totally buried are whitish to ivory in color. Most of these 'briers' have edible portions and have been used medicinally for centuries. S. rotundifolia roots are rich in starch and can be dried and ground into a powder for use in making cakes, puddings, sweet drinks resembling root beer, jelly or soups. I have read that raw young shoots can be added to salads or cooked like asparagus.