Unique Plants near the Thermal Springs

Tufa rock is being created by the thermal springs.

NPS Photo/Mitch Smith

A Special Habitat

There are a few special plants that have adapted to live near the thermal springs at Hot Springs National Park. Over thousands of years our springs have slowly deposited minerals forming what is called "tufa". Tufa is formed as lime-rich water evaporates, leaving behind a soft and porous calcium carbonate rich rock.Tufa deposits form a unique habitat for a diverse flora. Bryophytes (mosses, ferns, spleenworts etc.) and diatoms are well adapted and often found. The porosity of the tufa forms a wet habitat ideal for these types of plants. Porous rocks such as tufa have lots of surface area and create a large boundary layer around their edges that acts as a slightly different "micro-habitat" that retains water very well. Water is very important to the reproduction process of many of these species.

The interconnected components that make up the natural system of the hot springs creates a lot of these unique micro-habitats that allow very different species to live side by side. For example, a rare acidophilic (acid-loving) plant and one that depends on an alkaline environment have both been documented growing in the area around the hot springs.

 

Arkansas Bedstraw drawing on right: FDA
Woodland Stonecrop picture on left: CC photo by Fritz Flohr Reynolds

Unlikely Neighbors

Arkansas bedstraw (Galium arkansanum var.pubiflorum) is a rare variety of the more common bedstraws. It thrives in the acid soils of the chert and novaculite outcrops. “Bedstraw” plants have a sweet fragrance which actually gets stronger when they are dried. This trait caused them to be used to stuff mattresses in medieval times. Most of the plants have hairy or prickly stems and small white flowers.

The calcareous tufa deposited around the springs provides the alkaline environment needed by the rare woodland stonecrop (Sedum ternatum). Woodland stone crop is a member of the sedum family which includes succulents, such as the Jade Tree, that are grown as ornamentals. This rock-loving perennial usually sends up a single flowering branch and several shorter, leafier, non-flowering branches. Sometimes little plantlets grow along these leaves and drop to the ground to root and form new plants.

 

Hybrids

 

Artistic Rendition of the hybrid spleenworts

Becca Staszak - 2017

Novaculite outcrops on ridges and mountain tops above the springs are home to four unusual spleenworts: a lobed spleenwort (Asplenium pinnatifidum), the cliff spleenwort (Asplenium Bradleyi), the Scott’s hybrid spleenwort (Asplenium ebenoides) and the rare Graves hybrid spleenwort (Asplenium gravesi).

Spleenworts are a type of fern which means they are flowerless and seedless vascular plants which have true roots growing from a rhizome, fronds that uncurl upward, and they reproduce by spores.

Spleenworts get their name from the old belief, based on the doctrine of signatures, that the fern was useful for ailments of the spleen, due to the spleen-shaped sori, (spore cluster markings), on the backs of the fern fronds. Much of this same type of thinking went into the naming of many of our springs such as kidney and liver springs.

The hybrid spleenworts are rare in part because they are sterile and do not reproduce. Hybrids are the offspring of two different species or parents of the same species that have very different characteristics they are able to pass on to the next generation.

The "Graves Spleenwort" pictured on the bottom of the painting to the left by former Artist in Residence Becca Staszak, is a rare, sterile, hybrid fern, named for Edward Willis Graves (1882–1936). It is formed by the crossing of Bradley's spleenwort (A. bradleyi) with lobed spleenwort (A. pinnatifidum). It is only found where its parent species are both present; in practice, this proves to be only a few scattered sites in the Ozarks, Appalachian Mountains, Shawnee Hills, and here in the Ouachita Mountains.

 

Certain types of algal communities have adapted to be able to live in the, (143° degree average), temperatures of the thermal waters.

NPS Photo/ Thomas Waymouth

 

Many diatoms float under the Microscope.

USDA - Gordon T. Taylor - Stony Brook University

Diatoms

In a 2013 study, 16 species of unicellular algae, (diatoms), were found in or near the springs. They are the only plants that are able to live in the thermal springs. The study found 45 total species of "algae", 29 of them were cyanobacteria, ( Blue-Green Algae), which is technically not a plant. Cyanobacteria has no nucleus, no chloroplast, and no photosynthetic structures of true algae.The diatoms were only found near the lower temperature springs as they can only survive up to 95° F, (35° C).

Diatoms are single-celled algae that play a big role in keeping earth's ecosystem working. They're important mediators of carbon and oxygen cycles, an integral piece of marine food webs and the principal cyclers of silica, which constitutes about 25% of the Earth's crust. Over 20 percent of the oxygen we breathe comes from photosynthesis by diatoms!