In Photo 3 the arrows point to soil level and to their left you see the ‘root’ which is the basis for the ‘radicata’ epithet (derived from the Latin radix=root). That ‘root’ is part of the stem and this mushroom has arisen from buried wood. Obviously the length of the ‘root’ depends on the depth of the wood that the fungus had been feeding on. I have seen much longer ‘roots’, but with increasing depth of wood it becomes more difficult to extract the entire ‘root’.