1. Acid forest soils with a subsurface accumulation of metal-humus complexes.

Spodosols often occur under coniferous forest in cool, moist climates and are divided into five suborders: Aquods, Gelods, Cryods, Humods, and Orthods which are defined in this unit.

2. From the U.S. Soil Taxonomy soil-order classification system.
3. Etymology: from Greek spodos, "wood ashes" + -sol, Latin solum, "soil".