There is considerable diversity in the form and appearance of this species, with genetic diversity seeming to reach its highest level along the coast in the vicinity of the border between Oregon and California. It is tolerant of serpentine soils to the point that serpentine soils (along with surface water) can be used as a sign of its presence in southern Oregon. For this reason, it is a part of the unique plant community found in the serpentine barrens of the Siskiyou Mountains, along with Darlingtonia californica and Cypripedium californicum. It is usually found in wetlands although, like other rhododendrons, it does not grow with its roots submerged in water. It prefers both more moisture and more sunlight than Rhododendron macrophyllum, an evergreen rhododendron with a similar range.