Little Amphianthus - Amphianthus pusillus
By Chris Daves, SC Master Naturalist
Little amphianthus is a very small, aquatic herb belonging to the Figwort family. Other common names for this species include pool sprite and snorklewort. The U.S. Fish and Wildlife Service first listed it as a threatened species in 1988.
The distribution of little amphianthus is restricted to the Piedmont physiographic region of only three southeastern states: Alabama, Georgia, and South Carolina. A majority of the populations are located in Georgia. In South Carolina, only three populations are known to exist and include sites located in Lancaster, Saluda and York Counties.
Its typical habitat includes rock-rimmed temporary pools on weathered granite or gneissic outcrops. The outcrops can be large, isolated domes or gently rolling flatrocks. The pools are often referred to as vernal pools and are typically shallow, flat-bottomed, and have intact rims. The intact rims are an important feature in that they restrict drainage and thus allow the pools to hold water required by the species.
Ideal conditions within the vernal pools include shallow mineral soils that are sandy-silty and very low in organic material and nutrients such as nitrogen, phosphorus, and potassium. Pools retaining 1 to 4 inches of water for several weeks following a heavy rain provide sufficient habitat for the species.
Two other federally listed species, mat-forming quillwort (Isoetes tegentiformans) and black-spored quillwort (Isoetes melanospora) also share this specialized microhabitat with little amphianthus.
Little amphianthus is an ephemeral annual with its entire life cycle usually lasting less than a month. During the summer months, the vernal pools are often dry and the species persists only as seeds in the dried-out soil. Seed germination usually peaks in the late winter or early spring when light and rainfall conditions are adequate. The plant dies when the pools are desiccated by lack of rainfall.
Little amphianthus possesses two types of leaves: floating and submerged. Submerged leaves are narrow and arranged in a basal rosette. The single pair of floating leaves is oppositely arranged and greenish-purple. The floating leaves are ovate or rounded in shape and attached to a long, slender, underwater stem.
Depending on environmental conditions, flowering usually occurs in early spring (March to April). Flowers are borne in the axils of both types of leaves. Submerged flowers remain closed except when exposed to air. Only floating flowers are opened. A single, white to pale-purplish flower grows between the paired floating leaves. The fruits are in capsule form containing numerous dark-brown seeds. Seeds can lie dormant for several seasons until adequate amounts of water become available for germination.
Self-pollination appears to be the predominant form of sexual reproduction in little amphianthus. Cross-pollination does occur between individuals.
One of the largest threats to the species is destruction of its habitat via rock quarrying. Quarrying companies own approximately 10-20% of granite outcrops known to contain suitable habitat for the species.
Farm animals have contributed to the demise of the species through trampling of its habitat and depositing excessive amounts of fecal waste (i.e. nutrients) in the vernal pools. Extra nutrients in the pools result in eutrophication that causes algal growth and thus competition for carbon dioxide and light. Excessive soil accumulation in the pools causes invasion of more aggressive species that may shade out little amphianthus. The species is a poor competitor and requires high light intensity.
Many sites have been impacted by recreational abuse such as excessive foot traffic, motorcycles, bicycles, four-wheelers, and automobiles. Dumping of waste materials and fire-building in the pools also contribute to habitat destruction.
Conservation and preservation activities being implemented include tighter controls and restrictions on vehicular traffic and pedestrian activities. Protective fencing is being placed around suitable habitats where farm animal activity is occurring. Efforts have been made to form cooperative agreements with private landowners since most of the suitable habitat is under their control. Other efforts include land acquisition by conservation groups to protect remaining habitats and populations.
Forty-Acre Rock Heritage Preserve in Lancaster County in one of the few places in South Carolina in which little amphianthus can be found. On a recent late-October field excursion to Forty-Acre Rock, I along with Jake and Lori Duncan of D&D W.E.S.T. Consulting had the fortunate opportunity to view a flowering little amphianthus at an unusual time of year.
With flowering usually occurring in early spring, this untimely sighting may be due to lack of adequate rainfall this past spring. Apparently, the vernal pools were not able to retain enough water for the seeds to germinate during their usual time. However, the ideal conditions of enough light and rainfall to fill the pools occurred in October. It appears botanists should look for little amphianthus at other times of the year and not just in early spring.