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G803 Isoetes spp. - Pilularia americana - Callitriche heterophylla Granite Outcrop Pool Group

Type Concept Sentence: These southern granitic outcrop pools of Georgia, South Carolina, Alabama, and Texas are characterized by Isoetes spp., with other plants such as Pilularia americana and Callitriche heterophylla. These small rock depressions fill with water after heavy rains and stay flooded for several weeks in the winter and early spring, drying out in the summer.

Common (Translated Scientific) Name: Quillwort species - American Pillwort - Greater Water-starwort Granite Outcrop Pool Group

Colloquial Name: Southeastern Granite Outcrop Pool

Hierarchy Level:  Group

Type Concept: These southern granitic outcrop pools of Georgia, South Carolina, Alabama, and Texas are characterized by Isoetes spp., with other plants which tolerate inundation and very dry summer conditions, such as Pilularia americana and Callitriche heterophylla. These small rock depressions fill with water after heavy rains and stay flooded for several weeks or more in the winter and early spring; in the summer they dry out and can be very hot. Isoetes spp. and Crassula aquatica are among aquatic plants which use a type of Crassulacean Acid Metabolism (CAM) which allows survival in inundation and in extreme drought. This is a very distinctive vegetation type which supports a number of rare plants and which is restricted to seasonally flooded pools on granitic outcrops of Georgia, South Carolina, Alabama, and Texas.

Diagnostic Characteristics: This is a very distinctive vegetation type which is restricted to seasonally flooded pools on granitic outcrops of Georgia, South Carolina, Alabama, and Texas. These small depressions fill with water after heavy rains and stay flooded for several weeks or more in the winter and early spring. Isoetes spp. are characteristic, with other plants which tolerate inundation and very dry summer conditions, such as Pilularia americana and Callitriche heterophylla. There is a low amount of species overlap between the central Texas and southern Piedmont examples, which are presently represented by different associations in the same alliance.

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: A new association has been described for the granitic outcrop pools of the Llano Uplift in central Texas, characterized by Isoetes lithophila, Isoetes melanopoda, Pilularia americana, Callitriche heterophylla, and other plants. This vegetation is in the southern Piedmont of South Carolina, Georgia and Alabama, and in the Llano Uplift of central Texas. It probably is within the warm-temperate climatic zone, but not the coastal plain. The placement of this group in ~Atlantic & Gulf Coastal Plain Wet Prairie & Marsh Macrogroup (M067)$$ may need review. It could be placed in the broad ~Eastern North American Marsh, Wet Meadow & Shrubland Macrogroup (M069)$$, or with other wetlands found in central Texas in ~Great Plains Marsh, Wet Meadow, Shrubland & Playa Macrogroup (M071)$$.

Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: The vegetation is dominated by herbaceous annuals and perennials which tolerate very dry summer conditions and winter and early spring flooding and occur in small pools on granite outcrops (Hilton and Boyd 1996). These include emergent and floating-leaved herbaceous plants. Pools may be dominated by Isoetes spp., which are emergent or submerged fern allies, but look like graminoid plants. Isoetes melanospora and Isoetes tegetiformans use a type of Crassulacean Acid Metabolism (CAM) which allows survival in inundation and in extreme drought (Keeley and Zedler 1998, Shure 1999).

Floristics: In the southern Piedmont, this vegetation is dominated by Isoetes melanospora and/or Isoetes tegetiformans, and Amphianthus pusillus (= Gratiola amphiantha), all of which are endemic to seasonally flooded pools on granitic flatrocks of the southeastern United States. Other species which may occur in the pools or along the edges are Callitriche heterophylla, Cyperus granitophilus, Juncus bufonius, Juncus georgianus, Pilularia americana, and Rhynchospora globularis var. saxicola (= Rhynchospora saxicola) (McVaugh 1943, Burbanck and Platt 1964, Edwards et al. 2003, McMillan 2007). In addition, Diamorpha smallii may occupy adjacent marginal areas of this community, which are flooded for shorter periods of time (Hilton and Boyd 1996). In central Texas, examples occur in freshwater rock pools on granite outcrops of the Llano Uplift. These are characterized by Anagallis minima, Bacopa rotundifolia, Callitriche heterophylla, Crassula aquatica, Elatine brachysperma, Heteranthera limosa, Isoetes lithophila, Isoetes melanopoda, Juncus diffusissimus, Lepuropetalon spathulatum, Mimulus glabratus var. jamesii, Pilularia americana, and Plantago heterophylla (Walters and Wyatt 1982, Holmes et al. 2005, cited in Poole et al. 2007, Singhurst et al 2007).

Dynamics:  This vegetation is subject to winter and early spring flooding as well as very hot and dry summer conditions. Isoetes melanospora and Isoetes tegetiformans use a type of Crassulacean Acid Metabolism (CAM) which allows survival in alternating conditions of inundation and extreme drought (Keeley and Zedler 1998, Shure 1999). Amphianthus pusillus is apparently both microsite-limited and dispersal-limited (Hilton and Boyd 1996).
Environmental Description:  These small depressions in granitic rock outcrops become very dry and hot during summer conditions, but can remain flooded for several weeks or more in winter and early spring. These are small, but ancient ecosystems. There are broad similarities to outcrop pools on granite in other parts of the world, including southern Africa and western Australia (Keeley and Zedler 1998, Jocque et al. 2010).
Geographic Range: Vegetation of this group is found in the southern Piedmont from Alabama to South Carolina and on the Llano Uplift in central Texas.

Nations: US

States/Provinces:  AL, GA, MO, SC, TX


Confidence Level: Moderate

Confidence Level Comments: No Data Available
Grank: GNR

Greasons: No Data Available
Type Name Database Code Classification Code
Class 2 Shrub & Herb Vegetation Class C02 2
Subclass 2.C Shrub & Herb Wetland Subclass S44 2.C
Formation 2.C.4 Temperate to Polar Freshwater Marsh, Wet Meadow & Shrubland Formation F013 2.C.4
Division 2.C.4.Nd Eastern North American Temperate Freshwater Marsh, Wet Meadow & Shrubland Division D323 2.C.4.Nd
Macrogroup 2.C.4.Nd.2 Broadleaf Cattail - White Snakeroot - Rush species Marsh, Wet Meadow & Shrubland Macrogroup M069 2.C.4.Nd.2
Group 2.C.4.Nd.2.c Quillwort species - American Pillwort - Greater Water-starwort Granite Outcrop Pool Group G803 2.C.4.Nd.2.c
Alliance A1817 Quillwort species - Poolsprite Granitic Outcrop Pool Alliance A1817 2.C.4.Nd.2.c
Concept Lineage: No Data Available

Predecessors: No Data Available

Obsolete Names: No Data Available

Obsolete Parents: No Data Available
Synonomy: < Continental Climate Granite Outcrop Pools (Keeley and Zedler 1998b)
< Freshwater rock pools (Jocque et al. 2010)
< Seasonally water-filled rock pools (Porembski et al. 1997)
? Shallow Pool Communities (Quarterman et al. 1993)
= Shallow Pools (Shure 1999)
= Vernal (Temporary) Pools (Edwards et al. 2013)
= Vernal Pools (Singhurst et al. 2007)
= depressions on rock surfaces (McVaugh 1943)
= temporary rock pools (Walters and Wyatt 1982)
Concept Author(s): C.W. Nordman, in Faber-Langendoen et al. (2015)

Author of Description: C.W. Nordman and M. Pyne

Acknowledgements: The past work of Brendonck, Burbanck, Jocque, Keeley, McVaugh, Platt, Walters, Wyatt, Vanschoenwinkel, Singhurst, and Zedler has enabled understanding of these small wetland communities.

Version Date: 07-10-15
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