Populus heterophylla, known as the Swamp Cottonwood, also called the River Cottonwood, Downy Poplar, Swamp Poplar, or Black Cottonwood which is actually Populus trichocarpa, is a large deciduous Poplar belonging to section Leucoides of the larger Salindaceae family, found in wet bottom land forests.-Swamp cottonwood; Retrieved 2011-07-23 Reaching a height of at full maturity and in 20 years.