Tree
Buttress roots
Buttress roots are large, wide roots near the base of a tree that flare out from the trunk and help hold the tree upright.
Buttress roots are big roots right at the base of a tree. They spread out like braces and help the tree stand. A study in Arboriculture & Urban Forestry, a journal of the International Society of Arboriculture, describes them as roots near the base of the tree that support the tree and equalize mechanical stress.
On stumps, buttress roots make the base look wide and uneven. They may rise above the soil. A grinder can cut the visible parts, but they run underground and the thickest ones can make the job harder.
They are part of the root flare. Large ones may also show up as surface roots in a lawn. Ask for the stump diameter to include them when you request an estimate.