Physiognomy and Structure: The tree layer is dominated by tall (20-35 m in height) single-stemmed deciduous species. The canopy is overlapping, generally forming 60-100% cover. The shrub layer is also dense with up to 60% cover, and often multi-tiered, with both tall and short shrubs. The herbaceous layer is dominated by forbs with up to 20% cover. In parts of this alliance''s range, graminoid cover is primarily from introduced grass species.

Floristics: The tree canopy of this alliance is tall (to 30 m) and nearly always dominated by Populus deltoides, although Acer negundo, Celtis laevigata, Fraxinus pennsylvanica, Platanus occidentalis, Salix nigra, and Ulmus americana are also commonly encountered in various parts of this alliance''s range. Tree diversity is limited due to the dynamics of flooding and deposition/scouring of sediments. The shrub layer is sparse to dense, with species such as Cornus drummondii, Cornus sericea, Prunus virginiana, Salix exigua, and Symphoricarpos occidentalis. Herbaceous growth can be thick and lush but is often patchy and sparse due to frequent inundation. Herbaceous species found throughout the range of this alliance are not well known, but in parts of the range, species can include Pascopyrum smithii and Panicum virgatum (throughout the range), Carex spp., Juncus spp., Leymus cinereus, and Elymus canadensis (common in the northern Great Plains), and Amphicarpaea bracteata, Carex blanda, Geum canadense, Parietaria pensylvanica and others in the central Great Plains. Due to the frequent disturbance, weedy species are almost ubiquitous in the understory, especially Poa pratensis, Bromus inermis, Melilotus officinalis, Ambrosia spp., and Urtica spp.

Dynamics:  Cottonwood forests grow within an alluvial environment that is continually changing due to the ebb and flow of the river. Riparian vegetation is constantly being "re-set" by flooding disturbance. Cottonwood communities are early-, mid- or late-seral, depending on the age class of the trees and the associated species of the stand. Mature cottonwood stands do not regenerate in place, but regenerate by "moving" up and down a river reach. Over time, a healthy riparian area supports all stages of cottonwood communities. The process of cottonwood regeneration is well-documented. Periodic flooding events can leave sandbars of bare, mineral substrate. Cottonwood seedlings germinate and become established on newly-deposited, moist sandbars. In the absence of large floods in subsequent years, seedlings begin to trap sediment. In time, the sediment accumulates and the sandbar rises. The young forest community is then above the annual flood zone of the river channel. In this newly elevated position, with an absence of excessive browsing, fire, or agricultural conversion, this cottonwood community can grow into a mature riparian forest. At the same time, the river channel continually erodes streambanks and creates fresh, new surfaces for cottonwood establishment. This results in a dynamic patchwork of different age classes, plant associations and habitats. As cottonwoods mature, other tree species may become established. If the land surface is subject to reworking by the river, the successional processes will start over with erosion and subsequent flooding deposition. If the land surface is not subject to alluvial processes, for example on a high terrace, the cottonwoods will be replaced by upland shrub or tree species from adjacent areas.