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Isoetes junciformis D.F. Brunt. & D.M. Britton
Rush Quillwort
Federal Protection: No US federal protection
State Protection: No Georgia state protection
Global Rank: G1
State Rank: S1?
Element Locations Tracked in Biotics: Yes
SWAP 2015 Species of Greatest Conservation Need (SGCN): Yes
SWAP 2025 Species of Greatest Conservation Need (SGCN): Yes
2025 SGCN Priority Tier: Highest Conservation Concern
Element Occurrences (EOs) in Georgia: 1
Habitat Summary for element in Georgia: Low, seasonally flooded swales
Perennial herb, forming robust tufts of leaves. The rootstock (corm) is rounded, with two lobes. Leaves are 10 - 15.7 inches (25 - 40 cm) long, stiffly erect to somewhat curved, with an expanded base, tapering tip, 4 cross-walls, and single midveinl leaves are pale grayish lime-green except at the base where they pale pinkish-purple. Spores are produced in the sporangium, a brown-streaked chamber about 0.3 inch (7.5 mm) long in the leaf base, with a transparent membrane (velum) covering almost 40% of the chamber opening. Dozens of tiny female spores (megaspores), approximately 0.5 mm across and covered with a dense pattern of broad, low, broken ridges, may be seen with 25-30x magnification. Much smaller male spores (microspores) are produced on separate leaves but are indistinguishable without much higher magnification.
Quillworts are distinguished from flowering, wetland plants by their spongy leaves with conspicuous cross-walls and by the presence of sporangia in the flared base of the leaves. Blackfoot quillwort (Isoetes melanopoda) occurs in habitats similar to rush quillwort’s, and has similar leaves, but its velum usually covers less than 15% of the chamber opening; its megaspores are smaller and are more plainly patterned. Southern quillwort (I. flaccida) occurs in habitats similar to rush quillwort’s and also occurs in the southwest portion of Georgia’s Coastal Plain; it has long, flaccid, dark green leaves (4 - 24 inches, 10 - 60 cm) that are sprawling, not erect; its velum completely covers the spore chamber, which is colorless, not streaked with brown and its megaspores are smaller. Engelmann’s quillwort (I. engelmannii) also has long leaves (10 - 24 inches, 25 - 60 cm) and its velum covers 30-60% of the chamber opening; it is the most common quillwort in Georgia but is found mostly in the Piedmont. Appalachian quillwort (I. appalachiana) has megaspores with more distinctively thin-walled, reticulate ornamentation patterns. Boom’s quillwort (I. boomii) and Georgia quillwort (I. georgiana) both have larger, more coarsely ornamented megaspores and more extensive velum coverage.
Twelve quillwort species are state-listed or considered of Special Concern in Georgia. Information about each of these species may be found at these links:
Boom's Quillwort (Isoetes boomii) https://www.georgiabiodiversity.org/portal/profile?group=plants&es_id=17134
Appalachian Quillwort (Isoetes appalachiana) http://explorer.natureserve.org/servlet/NatureServe?searchName=Isoetes+appalachiana
Glade Quillwort (Isoetes butleri) http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=250076861
Florida Quillwort (Isoetes flaccida) https://www.georgiabiodiversity.org/portal/profile?group=plants&es_id=19963
Georgia Quillwort (Isoetes georgiana) https://www.georgiabiodiversity.org/portal/profile?group=plants&es_id=16950
Winter Quillwort (Isoetes hyemalis) https://www.georgiabiodiversity.org/portal/profile?group=plants&es_id=17363
Rush Quillwort (Isoetes junciformis) https://www.georgiabiodiversity.org/portal/profile?group=plants&es_id=18998
Black-footed Quillwort (Isoetes melanopoda) http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=250076862
Black-spored Quillwort (Isoetes melanospora) https://www.georgiabiodiversity.org/portal/profile?group=plants&es_id=22510
Broxton Rocks Quillwort (Isoetes "snowii," undescribed) https://bioone.org/journals/castanea/volume-83/issue-2/17-122/Interesting-Provocative-and-Enigmatic--Morphological-Observations-on-Southeastern-Quillworts/10.2179/17-122.full
Mat-forming Quillwort (Isoetes tegetiformans) https://www.georgiabiodiversity.org/portal/profile?group=plants&es_id=20422
Mountain Bog Quillwort (Isoetes valida) https://www.jstor.org/stable/1547604?seq=1#metadata_info_tab_contents
Seasonally flooded open swales adjacent to floodplain swamps, submerged with flowing water during spring rains but often completely drying as summer approaches.
Quillworts are seedless, non-flowering plants that reproduce by spores. Quillworts have a short, fleshy, rootstock called a corm; leaves are produced on the upper surface of the corm, roots on the lower surface. The leaves of rush quillwort wither and disappear during dry periods; however, the corm remains alive and will begin to produce leaves when there is again adequate water. Quillwort leaves have hollow chambers (sporangia) at the base where two types of spores are produced: tiny, dust-sized microspores develop sperm-producing structures, and larger (though still minute) megaspores produce eggs. Sperm swim to the eggs in available water and unite to form new plants. Quillworts compete poorly with other aquatic plants and are typically found in relatively sterile sand or silt or in frequently water-worn sites that support few or no other vascular plants.
Surveys are best conducted immediately following spring flood season when plants are most conspicuous and before the leaves have withered and disappeared; mature megaspores are best developed in late spring but can be found (from previous years’ growth) in the soil at the base of younger plants.
Isoetes junciformis is a Georgia endemic, found nowhere else in the world.
Ditching and draining wetlands, impounding streams, clearcutting in swamps and floodplains. Invasion by exotic pest plants.
| Threat 1 | Threat 2 | Threat 3 | |
|---|---|---|---|
| General Threat | Transportation & Service Corridors | Biological resource use | Human intrusions & disturbance |
| Specific Threat | None | None | None |
Isoetes junciformis is ranked S1? by the Georgia Department of Natural Resources, indicating that it is probably critically imperiled in Georgia but that additional information is needed to make a final ranking. It has been documented in one county in southwest Georgia in 2017 on private land.
Protect floodplains and swamps from damming, clearing, draining, filling, pollution run-off, and sedimentation from upland disturbances. Eradicate exotic pest plants.
Brunton, D.F. 2015. Key to the quillworts ("Isoëtes": Isoëtaceae) of the southeastern United States. American Fern Journal 105(2): 86-100. https://www.jstor.org/stable/44076059?seq=1#metadata_ info_tab_contents
Brunton, D.F. and D. M. Britton. 1999. Rush quillwort (Isoetes junciformis, sp. nov.), a new pteridophyte from southern Georgia. American Fern Journal 89(3): 187-197.
GADNR. 2020. Element occurrence records for Isoetes junciformis. Georgia Department of Natural Resources, Wildlife Resources Division, Social Circle, Georgia.
Musselman, L.J. 2001. Georgia quillworts. Tipularia, Journal of the Georgia Botanical Society 16: 2-19, 40.
NatureServe. 2019. Isoetes junciformis comprehensive report. NatureServe Explorer. Arlington, Virginia. http://explorer.natureserve.org/servlet/NatureServe?searchName=Isoetes+junciformis
Weakley, A.S. 2015. Flora of the southern and mid-Atlantic States. University of North Carolina Herbarium, University of North Carolina, Chapel Hill. http://www.herbarium.unc.edu/flora.htm
Linda G. Chafin and Daniel F. Brunton
L. Chafin and D. Brunton, Dec. 2008: original account
K. Owers, Feb. 2010: added pictures
L. Chafin, March 2020: updated original account.
