The vegetation of the George Washington Memorial Parkway includes a complex of upland, floodplain forest, and tidal marsh communities, as well as several rare vegetation types that occupy the bedrock terraces, exposed rocks, and frequently flooded river shores. Although disturbed, secondary forests are common in formerly cleared areas of the Park much of the contemporary forest consists of maturing second-growth stands that belong to the following ecological groups (Fleming et al. 2004): basic mesic forest, mesic mixed hardwood forest, acidic oak-hickory forest, oak/heath forest, and Piedmont / Mountain floodplain forest. Older-age stands (> 100 years) occur on ridges at both the northern and southern ends of Great Falls Park. Abrams and Copenheaver (1999) documented several white oak (Quercus alba) individuals more than 200 years old on the northern ridge.
The Park's complex topography, varied hydrological influences, and diversity of flood-influenced habitats fosters a corresponding diversity of vegetation types, some of them of significant conservation concern. On the bedrock terrace, the ancient oxbow west of the Old Carriage Road in Great Falls Park supports one of the largest known examples in Virginia of a Coastal Plain / Piedmont basic seepage swamp (G4G5/S2). On flats along the rocky rim of the terrace are two other rare forest communities that are scoured by periodic catastrophic floods: the Riverside Bedrock Terrace Pine Woodland (G1?S1), known only from the Potomac Gorge in Virginia and Maryland and the New River Gorge in West Virginia; and the Potomac River Bedrock Terrace Oak - Hickory Forest (G1G2S1), which is endemic to the Potomac Gorge. Rare communities of exposed rocks on the lower portions of the bedrock terrace, the gorge rim, and the river channel shelf include the Central Appalachian / Piedmont riverside prairie (G2G3S1) and the Potomac Gorge riverside outcrop barren (G2?S1). A substantial number of regionally rare plants are associated with these rocky habitats including Nantucket shadbush (Amelanchier nantucketensis), sterile sedge (Carex straminea), western sunflower (Helianthus occidentalis), and sticky goldenrock (Solidago racemosa) (Townsend 2004).
Turkey Run Park puts on one of the most spectacular spring wildflower shows found anywhere in the State of Virginia. The rich floodplain forest floors are swept in carpets of blue by the abundance of Eastern Bluebells (Mertensia virginica) and also provide habitat for many state listed rare species of herbaceous plants.
Along the shores of the Potomac River, near the southern end of the Parkway, lies Dyke Marsh, one of the largest tidal marshes in the jurisdiction of the National Park Service. The vegetation here is dominated by narrow-leaved cattails (Typha angustifolia), but also contains some large stands of arrow arum (Peltandra virginica), Sweet flag (Acorus calamus), yellow bullhead lily (Nuphar luteum), jewelweed (Impatiens capensis), river bullrush (Scirpus fluviatilis), and wild rice (Zizania aquatica).
Abrams, M.L. and C.A. Copenheaver. 1999. Temporal variation in species recruitment and dendroecology of an old-growth white oak forest in the Virginia Piedmont, USA. Forest Ecology and Management 124: 275-284.
Fleming, G.P., P.P. Coulling, K.D. Patterson, and K.M. McCoy. in prep. The natural communities of Virginia: classification of ecological community groups. Second approximation. Natural Heritage Technical Report 04-01. Virginia Department of Conservation and Recreation, Division of Natural Heritage, Richmond, VA.
Townsend, J.F. 2004. Natural Heritage resources of Virginia: rare plants. Natural Heritage Technical Report 04-06. Virginia Department of Conservation and Recreation, Division of Natural Heritage, Richmond, VA. 56 pp. plus appendices