Granite Flatrock Barren

By Drew Chaney, Center for Urban Habitats

The Southern Piedmont Granitic Flatrock is a globally rare plant community restricted to the Piedmont from Alabama north to south-central Virginia, occurring on exposed bedrock outcrops of granite and related rocks, where streams have eroded the rock smooth over time, creating a unique ecological niche where lichens and mosses colonize bare rock and small depressions and moss mats collect moisture and soil, creating ephemeral microhabitats in which the community’s vascular flora find a place to call home.

Peat moss (Sphagnum sp.)

This August, I visited a relatively large and well-known example of this community in Lunenburg County, in the southern Virginia Piedmont. This site is located on a band of quartzofeldspathic gneiss that crosses the Nottoway River, creating a series of smooth, gently sloping ledges over which the river flows, dropping about 70 feet in elevation from the top of the “falls”. These outcrops support a good example of the Piedmont Granitic Flatrock community as it occurs in Virginia. Growing on the rocks were a variety of mosses and lichens, displaying a variety of subtly beautiful colors and textures. Some of the vascular plants observed were rough buttonweed (Diodia teres), the eastern prickly-pear cactus (Opuntia humifusa), our only native cactus, the aptly named common hairsedge (Bulbostylis capillaris), and most interesting of all, the delicate and intriguing glade rushfoil (Croton willdenowii), a species I had never seen before. This species, though not restricted to this community type, is rather uncommon in Virginia, being found only on bedrock outcrops and barrens.

Glade rushfoil (Croton willdenowii)

Several species of plants are endemic to granite flatrock barrens, being found nowhere else. Of these, four true endemic are known from Virginia: granite flatsedge (Cyperus granitophilus), Piedmont quillwort (Isoetes piedmontana), Small’s purslane (Portulaca smallii), and elf-orpine (Diamorpha smallii). All of these are quite rare in Virginia, being known from no more than a handful of sites in the state, and in the case of Diamorpha and Isoetes, one location each.

A selection of mosses

None of these four species are present at the site I visited, either they were never there to begin with, or the relatively heavy human impact on this site (it is located not far off of a main road, and has been a popular swimming hole for years) has extirpated them long ago, but the community is still one of Virginia’s largest and most beautiful examples of the community. As I walked back to the car, I crossed through a powerline right-of-way where I encountered an abundance of sweet goldenrod (Solidago odora) and the spurred butterfly-pea (Centrosema virginianum) in full bloom, a reminder of the sunny woodlands and savannas that historically covered thousands of acres of Southside Virginia’s uplands.

Clouded skipper (Lerema accius) on spurred butterfly-pea (Centrosema virginianum)

Blue-ringed dancer (Argia sedula)

Photographs by Drew Chaney