Well, the first step we need to take is to find out if it's a fungus or plant. Then we can move towards smaller and smaller classifications.
Are there any signs of any spore-bearing surface?
Are you sure the "root" is a root, or is it mycelia? If it IS a plant, it's vascular seeing as it has a true root. Look for vascular tissue (xylem and phloem, wikipedia has decent articles on each of these.) If it doesn't have vascular tissue, it's either a non-vascular plant or a fungus. If it is non-vascular, it won't grow too tall, because of its lack of vascular tissue.
As Mokele suggested, it could be a non-photosynthetic plant. Those have a parasitic relationship with fungi. I don't know too much about those.
Ehhh, I hope I helped somehow. Get back to me if you find out anything new about this organism!