Life on the Rock

 

A granite rock outcrop showing a variety of plant types during an April visit. 
Clover Community Park, Clover, South Carolina.

The granite rock outcrops of the Southeastern Piedmont host an impressive array of rare and beautiful plants.  Spring is the best season the enjoy these unique ecosystems and experience this wonderful flora. 

 

A large solution pool with Diamorpha smallii, Minutartia sp.
and Isoetes sp. 40 Acre Rock, Lancaster County, South Carolina.

Granite rock outcrops are ancient in origin.  Hundreds of millions of years ago the area that is now the Piedmont experienced extreme vulcanism. In some cases, the magma never reached the surface but cooled and crystalized underground to form granite.  Tectonic uplift and erosion exposed portions of this granite.  In some places the outcrops are mountains rising above the surrounding country.  Stone Mountain, Georgia is the most dramatic of these.  In other places, the outcrop is a flat rock surrounded by forest. 

Prickly Pear Cactus (Opuntia humifusa) is adapted to dry conditions
and thrives on the Piedmont granite rock outcrops.
Dunn's Mountain Park, Rowan County, North Carolina.

Outcrops are impermeable stone and the plants that grow on them are adapted for a desert-like life.  Rainfall is typically the only source of water for the plants that call outcrops home.  Many of these plants reproduce quickly before the water on the outcrop dries up.

 

Peppered Rock-shield Lichen (Xanthoparmelia conspera) on granite.

Clover Community Park, Clover, Lancaster County, South Carolina.  

The first plants to colonize outcrops are lichens and mosses.  These hardy pioneers grow directly on the rock surface.  Lichens and mosses release acids that start converting stone to soil. Grimmia laevigata, Dry Rock Moss, is one of the species that live on bare rock.  When dry, this moss looks almost black but greens up when wet.  The action of erosion and pioneer plants make small depressions, called solution pools.  Over time, soil accumulates and herbaceous plants can take root.  When plants in the pools die they add organic matter to the thin, rocky soil.  As more soil builds up, hardy trees like pines and junipers colonize the outcrop. 

Light gray Reindeer lichen Cladonia sp. growing among various mosses.
Dunn's Mountain Park, Rowan County, North Carolina.

A single red plant of Elf Orpine, the black moss
Grimmia laevigata and the lichen Cladonia sp. grow at
Dunn's Mountain Park, Rowan County, North Carolina. 

In early April, granite rock outcrops in erupt with color.  Three tiny plants, Diamorpha smallii (Elf Orpine),  Minuartia uniflora (Piedmont Sandwort) and Minuartia glabra (Appalachian Stitchwort) burst out red and white in the solution pools.  Diamorpha smallii stands about three inches tall.  It makes bright red, succulent leaves that store water, which is in short supply on the rock.  Elf Orpine has flowers with four white petals and each petal is decorated with a red spot.   Diamorpha smallii is endemic to the Southeastern United States and limited to the rock outcrop habitat. 

 

A solution pool filled with Elf Orpine (Diamorpha smallii).
40 Acre Rock, Lancaster County, South Carolina.

Closeup of Diamorpha smallii.
Clover Community Park, Clover, South Carolina.

Piedmont Sandwort and Appalachian Stitchwort are also granite rock outcrop specialists. Appalachian Stitchwort is about twice as tall as Piedmont Sandwort and both have green leaves and five-petaled, white flowers.  Diamorpha and the two species of Minuartia often occur in the same solution pools and light it up with red and white.  

Piedmont Sandwort (Minuartia uniflora) flowering in a small solution pool.
40 Acre Rock, Lancaster County, South Carolina. 

Appalachian Stitchwort and the moss Grimmia laevegata.
40 Acre Rock, Lancaster County, South Carolina. 

Woolly Ragwort (Packera tomentosa) is a member of the sunflower family and grows mainly in the sandy soil of the Coastal Plain of the Southeast.  When it does occur on the Piedmont it is on rock outcrops.  This attractive plant has hairy, green leaves and an inflorescence of yellow ray and disk flowers.  Wooly Ragwort is much taller than Elf Orpine and Piedmont Sandwort that grow in the same area.  

Wooly Ragwort (Packera tomentosa) flowering in a 
bed of the moss (Polytrichum sp.) 
Clover Community Park, Clover, South Carolina.

False Garlic (Nothoscordum bivalve) is a relative of onion and garlic.  Like Wooly Ragwort, it is common on the Coastal Plain but also grows on Piedmont granite rock outcrops.  False Garlic makes star-shaped, white flowers and lacks the strong odor onion or garlic.    

False Garlic (Nothoscordum bivalve).
40 Acre Rock, Lancaster County, South Carolina.

Quillworts are members of the genus Isoetes, and dominate some of the solution pools on outcrops.  Quillworts look like grass in the shallow water but are more closely related to ferns.  Isoetes makes no flowers or fruits but reproduces by spores produced at the base of its leaves.  Identification of Quillworts is difficult because different species can hybridize and spontaneously double their chromosome number. 

 

Quillworts (Isoetes sp.) growing in a solution pool.  
Clover Community Park, Clover, South Carolina.

A single plant of Isoetes sp. This plant was collected 
by a researcher studying this rare plant.
40 Acre Rock, Lancaster County, South Carolina.

Granite rock outcrops have been used and abused by people for centuries.  Outcrops are natural sites to quarry the granite for construction and headstones.  Some flat outcrops have been turned into parking areas.  Recreation is also a threat to the rare and threated species that call outcrops home.  All-terrain vehicle drivers, motorcyclists, bikers and hikers plow through solution pools killing plants.  Broken glass litters some outcrops and graffiti is an issue in many areas.  Despite these problems, granite rock outcrops, particularly in spring, can be magical places. 

Diamorpha smallii flowering in a field of shattered glass.
Clover Community Park, Clover, South Carolina. 

Floating World

 

A mixed group of floating water plants.  
Palm Beach County, Florida

Afloat on the water, plants experience two dramatically different worlds.  One is bright, hot and dry, the other is dim, cool and wet. Some floating plants are rooted to the bottom and others sail about, moved by wind or current.  Many floating plants survive and thrive at this odd interface and we will look at just a few. 

Sargassum fluitans, Broad-leaf Gulfweed, floating in the clear blue water
of the Gulf Stream off Cape Hatteras, North Carolina. 

One marine floating plant is a seaweed in the genus Sargassum.   This brown alga floats at the surface of the ocean carrying out photosynthesis.  Sargassum never attaches to the ocean floor and can drift for long distances.  Sargassum supports many species of animals and microbes and will often wash up on Atlantic or Gulf beaches.  The North Atlantic Gyre is in the center of the ocean and is bounded on all sides by currents.  In the gyre, an area called the doldrums, have calm winds and little current.  Here vast amounts of Sargassum accumulates to form the Sargasso Sea.  Unfortunately, plastic trash also accumulates in the gyre and makes the North Atlantic Garbage Patch. 

 

A fresh-water swamp with a mix of floating plants. 
Colleton County, South Carolina. 

Freshwater ecosystems have many floating plants.  They generally grow in still or slow-moving water found in swamps, ponds, marshes and lakes. Fragrant Waterlily, Nymphaea odorata, grows throughout Central and North America.  This plant has a rhizome, an underground stem, rooted in the bottom of the body of water.  Long petioles bear the large, round, notched leaves that float on the surface.  Nymphaea odorata makes beautiful, fragrant white flowers that give the plant its name. The upper surface of the floating leaf has a waxy layer to prevent water loss.  Stomates, pores that allow CO₂ to enter and O₂ to exit the leaves are also on the upper leaf surface.  The lower leaf surface has neither stomates nor a waxy layer since that side of the leaf is in the water.    

Fragrant Waterlily (Nymphaea odorata).
Rowan County, North Carolina.

Another rooted water plant with floating leaves is Nuphar advena, Spatterdock.  This plant is found in both the old and new worlds and has large leaves that are deeply cut at the base.  Spatterdock makes a compact yellow flower that extend above the surface of the water.  

Spatterdock (Nuphar advena). Collier County, Florida.

Water-shield, Brasenia schreberi, is yet another water plant that is rooted to the bottom.  Its elliptical, shield-shaped leaves are smaller than those of Fragrant Waterlily and Spatterdock.  Water-shield leaves can grow in dense clusters in their still water habitat.  The leaves produce mucilage on the lower surface that may protect the plant from herbivores and prevent algal growth.  All three of these rooted water plants have air spaces in their leaves to give them buoyancy and to help transfer oxygen to the roots that may be in the anaerobic mud bottom of a pond.   

Water-shield (Brasenia schreberi).
Georgetown County, South Carolina.

Many floating plants are not rooted to the bottom but float freely on the surface.  One plant with this way of life is Water Lettuce, Pistia stratiotes. This pan-tropical plant is in found in the Southeastern United States and may be an introduced species.  Water Lettuce has a rosette of leaves that resembles a head of lettuce. Pistia stratiotes is a fast-growing plant and may cover the entire surface of ponds or canals and cause fish kills.  

Water Lettuce (Pistia stratiotes) floating in a pond.
Palm Beach County, Florida.

Water Lettuce and the water fern Salvinia minima. 
Palm Beach County, Florida. 

Common Duckweed, Lemna minor, a tiny, free-floating plant has leaves that are just a few millimeters in diameter with each plant having a single root. It is found in ponds and ditches worldwide.  Common Duckweed rarely flowers and the plant reproduces by fragmentation.  Lemna minor grows rapidly and has a number of uses.  Common Duckweed is used as an animal feed, it is important in wastewater treatment because it removes inorganic nutrients and it accumulates toxic heavy metals.  

Common Duckweed (Lemna minor) in a swamp forest. 
Rowan County, North Carolina.

Salvinia minima is a floating fern.  Its common name, Water Spangles, describes its sparkling appearance on the surface of a pool.  Salvinia minima has round floating leaves that are ¾ inch in diameter and hairs on the upper surface that repel water.  This fern has no roots but it does have highly branched underwater leaves that play the role of a root system.  Salvinia minima is native to Central America and the West Indies.  It is considered and invasive species throughout the Southern United States. 

Water Spangles (Salvinia minima) a water fern growing in a cypress swamp.
Palm Beach County, Florida.

Golden Club, Oronitum aquaticum is our final floating plant. It grows in slow moving streams and ponds in the Eastern United States and is rooted in the mud.  Another common name for this plant is Never-wet because its leaves repel water.  Golden Club has unique flowers that gives the plant its name. The flowers have white stalks tipped with tiny golden blooms.  

Leaves and flowers of Golden Club (Oronitum aquaticum).

Rowan County, North Carolina. 

A drop of water beaded up on the leaf of Golden Club. 
This water repulsion shows why this plant is also called Never-wet. 
Rowan County, North Carolina.

Plants in the floating world range from the oceans to freshwater ponds.  They may be as tiny as Common Duckweed or as large as Fragrant Waterlily.  But all these plants share adaptations that allow them to live at this intersection of air and water.