Riverine Aquatic Beds
The floating and submergent herbaceous vegetation of this group inhabits flowing streams with water depths that exclude emergent species but permit bottom rooting of aquatic species. These communities occur throughout the eastern United States. They are poorly inventoried in Virginia, but are known to occur in rocky shallows along many of the major mountain and Piedmont rivers. They are particularly well developed in base-rich waters of the Shenandoah River (including its two forks), the James River, and portions of the Roanoke River. Characteristic species include water stargrass (Heteranthera dubia), tapegrass (Vallisneria americana), pondweeds (Potamogeton spp.), waterweeds (Elodea canadensis and Elodea nuttallii), and naiads (Najas spp.). Horn-leaf riverweed (Podostemum ceratophyllum) is often abundantly rooted on shallowly submerged boulders and rock outcrops. Sluggish shoreline eddies and pools often support mats of floating duckweeds (Lemna spp.), duckmeal (Spirodela spp.), and eastern mosquito fern (Azolla caroliniana). Water pollution is a serious threat that can cause major declines or die-offs of aquatic vegetation in this group.
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An aquatic bed dominated by water stargrass (Heteranthera dubia, with yellow flowers) and Illinois pondweed (Potamogeton illinoensis, with wide leaves) covers the James River in Buckingham County. Photo © Irvine Wilson.
The two community types nested under this group are based on existing associations in the USNVC and are broadly consistent with stands observed by DCR-DNH ecologists along inland rivers (e.g., the Potomac, Shenandoah, and James) in the northern half of Virginia. Inventory of this group is clearly needed, although it is limited by accessibility issues and difficulties in quantitative sampling and will likely be considered a relatively low priority by DCR-DNH in the near future. Click on any highlighted CEGL code below to view the global USNVC description provided by NatureServe Explorer.