Desert truffles, Terfezia and allies, are mycorrhizal with Helianthemum spp (Cistaceae) and probably other plants. There is some literature on this, but I dont have references handy. Not al ectomycorrhizal hosts are trees, or even woody plants, e.g. Kobresia myrosoides (Cyperaceae) is ectomycorrhizal and a sedge relative. todell at u.washington.edu