Flora of a Flat-Rock granite outcrop near Liberty, in Pickens County, South Carolina — 2013-04-30

Recently a friend of mine, Diane Creaton, took me to a location that I had known about for many years, but I had never visited it since I didn’t know how to get there. It is what’s loosely called a “Flat-Rock granite outcrop”. These formations are composed of unbroken granite and granite-gneisses and are implaced within Precambrian metamorphic rocks which are scattered on the eastern side of the Appalachian Mountains in the southern states of Virginia, North Carolina, South Carolina, Georgia, and Alabama. These formations have been exposed, undoubtedly, due to the combination of uplift and erosion. All of that is well and good, but the best part is the flora which has evolved to thrive on these formations. It is both unusual and sometimes quite colorful, and it has found a niche that has remained undisturbed for millenia.

An excellent paper dealing with Flat-Rock formation and its flora (although its botanical references are somewhat dated), is The Vegetation of the Granitic Flat-Rocks of the Southeastern United States. The author is Rogers McVaugh, and the source: Ecological Monographs, Vol. 13, No. 2 (Apr., 1943), pp. 119-166, published by: Ecological Society of America. Much of what I have learned about this Flat Rock flora has come from this paper and from tagging along to similar sites with other nature lovers.

The site which is the subject of this blog post is found in Liberty, South Carolina, and it mimics in many ways the classic South Carolina site known as Forty Acre Rock Heritage Preserve in Lancaster County. However, it is much smaller and does not hold as many rare species as does Forty Acre Rock. Having said that, I will attempt to describe the flora that I have seen on this Flat-Rock granite outcrop.

When I first arrived at the site, I was met with a large expanse of relatively flat, unbroken granitic rock surrounded by cedars, pines, and southern hardwoods. The rock itself is mostly covered by different types of mosses and lichens. The dark, cushion-like moss is called Grimmia laevigata or Grimmia dry rock moss. The gray/white lichen is Xanthoparmelia conspersa or Peppered Rock-Shield Lichen. On dry days (such as the day on which I photographed it), the moss is a very dark gray — almost black color. It will appear dark green after a rain shower. It grows only on the granite outcrop and not in the surrounding woods. The lichen grows on the granite and breaks it down over many, many years. Lichens are known for their soil-building ability — converting hard rock to sand/soil. These two plants are usually the earliest to inhabit the rock face.

The very next thing that I noticed was the bright red mats of Diamorpha smallii or Elf Orpine. The plants are from 1 inch (2.5 cm) to 3 inches (7.5 cm) tall, and when they are in flower, appear to be dusted with “sugar”. The exceedingly small, four-petaled white flowers cover the top of the mat of plants:

The plants prefer to grow in the vernal pools which exist only during seasonal wet periods such as we have in late spring. These pools contain the product of corrosive action of the lichen — sandy soil which provides a substrate for the roots to penetrate on shallow depressions in the granite rock.

An up-close view of Elf Orpine shows how strange this plant really is:

Each plant has a number of very succulent, rounded leaves and supports as many as a eight, bright white flowers. The leaves and stem are bright, scarlet red. The plants on the left, below, are still in bud:

Most of the trees in the woods surrounding this large expanse of rock are Juniperus virginiana or Eastern Red-cedar. Many of these trees attain a considerable height and girth even though they are anchored in less than 1 foot (30 cm) of loose soil:

Another tree that is quite plentiful at this site is a Pinus virginiana or Virginia pine:

Previously, I mentioned the vernal pools which are scattered in the flatest portions of the outcrop. Here, one can find a curious, grass-like plant known as Isoetes or Quillwort. These bad boys are notoriously difficult to identify, so this one will remain nameless until I can wrangle an Isoetes expert to help me out. Here is an image of one of the pools that has a robust growth of Isoetes and sedges:

Around the edge of this pool, I also found dozens of tiny, black tadpoles — some beginning to sprout rear legs:

Another plant which is common to these pools is Minuartia uniflora or Piedmont Sandwort:

There is also its much smaller version (which I am not convinced it shouldn’t be named a separate species) that grows in the same pools. The “typical” version grows to about 4-5 inches (10-12.5 cm) and has a flower that may be as wide as 1/3 of an inch (~8 mm). The smaller version seldom reaches 2 inches (~4 cm) tall and has a flower that is generally less than 1/8 inch (2-3 mm) wide.

Some of the pools have been filled in with sand and other debris over time, and they support a number of plant species:

One species in particular is quite lovely. It is Tradescantia hirsuticaulis or Hairystem spiderwort. Its color ranges from a royal purple to deep rose:

In other filled-in pools and in the moss around the edge of the rock, one can reliably find clumps of the yellow-flowered Packera tomentosa or Wooly Ragwort:

Where the edge of the surrounding woods meets the bare rock, there is a wide, dense boundary of Polytrichum commune or Common haircap moss looking for the world like tiny trees all planted in neat rows:

‘Tis the season for new growth and fecundity, so I’m including the reproductive parts of this lovely moss. On the left are the flower-like male organs of this plant, and on the right are the relatively tall (4 inch or 10 cm), ripening spore capsules:

Growing in this thick bed of moss, one can find a rather tall (for its species) Bluet. The ones I photographed were about 4 inches (10 cm) tall. I’m lacking the identification on this one but I do have an image:

A plant that might seem, to some, to be odd growing in the South, is Opuntia humifusa or Eastern Prickly Pear Cactus. It was not yet in bloom, so I have taken the liberty to provide an image of a couple of its flowers taken in another nearby location during the summer season:

Finally, there is one other flower that can be found in the margins of the pools and growing in the mosses. It is Nothoscordum bivalve or Crowpoison. I believe it is also called False Garlic, but it does not have the garlic smell…

What a wonderful place, and it’s so close to home. As I mentioned, this site is protected but not under state authority. I hope the state Heritage Preserve program will consider adding it to its wonderful collection of protected sites. So far, it has not been vandalized by miscreants as have other Flat-Rock sites in the state. Apparently, the “empty” space provides a canvas for those with little minds: “Fools names like fools faces are often seen in public places…”

There is a bit of broken glass here and there, but thank Goodness no spray paint! In this part of the world, breaking beer bottles on the rock apparently gives the same amount of pleasure as shooting at road signs. Go figure…

It has been one of my joys to document (as I am able) the botanical treasures of this special place. Who knows what remains to be discovered in other seasons…

— Jim