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Isoetes melanospora Engelm.
Black-spored Quillwort
Federal Protection: Listed Endangered
State Protection: Endangered
Global Rank: G1?
State Rank: S1
Element Locations Tracked in Biotics: Yes
SWAP High Priority Species (SGCN): Yes
Element Occurrences (EOs) in Georgia: 18
Habitat Summary for element in Georgia: Vernal pools on granite outcrops
Perennial herb with a bulb-like base and forking roots. Leaves are usually 1 - 3 inches (3 - 8 cm) tall, very narrow with a pointed tip and a wide base that overlaps with other leaf bases to form a round, bulb-like underground base; each leaf has a single vein and contains 4 hollow air chambers separated by partitions. Spores are produced in a cavity (sporangium) in the leaf base, the cavity completely covered by a translucent membrane (velum) and containing dozens of tiny black to light gray female megaspores, approximately 0.3 - 0.4 mm wide, with slightly dimpled surface ornamentation (seen with 30x magnification). Male microspores, which are produced on separate leaves, are also present but are dust-sized and 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. Piedmont quillwort (Isoetes piedmontana) occurs in muddy seeps on granite outcrops. Its leaves are 2¾ - 6 inches (7 - 15 cm) long with brown to blackish bases; its megaspores are larger than black-spored quillwort’s and have a conspicuously dimpled ornamentation; Piedmont quillwort’s sporangium is only partially covered by the velum. Black-spored quillwort occurs with Piedmont quillwort (Isoetes piedmontana) on several outcrops and has been known to hybridize with it.
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
Shallow, temporarily flooded, flat-bottomed pools formed by natural erosion on granite outcrops. The pools are seasonally inundated by winter and early spring rains and by seepage from surrounding habitats; they are usually completely dry during the summer and fall.
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 disappear during dry periods; however, the corm is still alive and will begin to produce leaves when there is adequate water. Spores are produced in chambers at the base of the leaves in May and June and are released from the chamber when the leaf base deteriorates during summer’s dry, hot weather. Spores usually remain near the parent plant but may be dispersed by flowing water or insects. Some leaves produce megaspores, which crack open to expose tiny egg-producing structures; other leaves produce microspores, which develop sperm-producing structures. Egg and sperm unite and form new plants.
Plants are visible throughout the winter and spring and also following rainy periods in the summer.
Black-spored Quillwort is endemic to the Piedmont of Georgia and South Carolina. The South Carolina population is atypical, however, and may involve hybridization with Isoetes piedmontana.
Quarrying of granite outcrops, trash dumping, off-road-vehicle use, horseback riding, cattle trampling, and development of woodlands surrounding granite outcrops. Within the pools, the exotic species Weak Buttercup (Ranunculus pusillus) and native species Water-starwort (Callitriche heterophylla) are competing with Black-spored Quillwort and associated rare species. In areas surrounding the outcrops, Japanese Honeysuckle (Lonicera japonica) and Chinese Privet (Ligustrum sinense) are the biggest threats.
Isoetes melanospora is ranked S1 by the Georgia Department of Natural Resources, indicating that it critically imperiled in Georgia. It is listed as Endangered by both the U.S. Fish and Wildlife Service and the State of Georgia. Eighteen populations have been documented in Georgia, 11 in the last 20 years. Only six occur on conservation land and at least five have been destroyed by granite quarrying.
Protect granite outcrops from quarrying, trash dumping, and off-road vehicle use. Direct foot traffic away from rare plant sites and rock pools. Create no-impact buffer zones and limit development around outcrops. Eradicate exotic pest plants.
Brunton, D.F. 2015. Key to the quillworts (Isoetes: Isoetaceae) of the southeastern United States. American Fern Journal 105(2): 86-100. https://www.jstor.org/stable/44076059?seq=1#metadata_ info_tab_contents
Chafin, L.G. 2007. Field guide to the rare plants of Georgia. State Botanical Garden of Georgia and University of Georgia Press, Athens.
GADNR. 2020. Element occurrence records for Isoetes melanospora. Georgia Department of Natural Resources, Wildlife Resources Division, Social Circle, Georgia.
Haefner, K.D. and R.D. Bray. 2005. Taxonomic reassessment of North American granite outcrop Isoetes species with emphasis on vegetative morphology and I. piedmontana (Pfeiffer) Reed sensu lato. Castanea 70: 204-221. https://bioone.org/journals/Castanea/volume-70/issue-3/04-29.1/Taxonomic-Reassessment-of-North-American-Granite-Outcrop-Isoetes-Species-with/10.2179/04-29.1.full
Musselman, L.J. 2001. Georgia quillworts. Tipularia, Journal of the Georgia Botanical Society 16: 2-19.
NatureServe. 2019. Isoetes melanospora comprehensive report. NatureServe Explorer. Arlington, Virginia. http://explorer.natureserve.org/servlet/NatureServe?searchName=Isoetes+melanospora
Patrick, T.S., J.R. Allison, and G.A. Krakow. 1995. Protected plants of Georgia. Georgia Department of Natural Resources, Natural Heritage Program, Social Circle.
Snyder, L.H., Jr. and J.G. Bruce. 1986. Field guide to the ferns and other pteridophytes of Georgia. University of Georgia Press, Athens.
Taylor, W.C., N.T. Luebke, D.M. Britton, R.J. Hickey, D.F. Brunton. 1993. Isoetes melanospora species account. Flora of North America. Vol. 2, Pteridophytes and Gymnosperms. Oxford University Press, New York. http://beta.floranorthamerica.org/Iso%C3%ABtes_melanospora
USFWS. 2019. Three granite outcrop plants: black-spored quillwort (Isoetes melanospora), mat-forming quillwort (Isoetes tegetiformans), and little amphianthus (Amphianthus pusillus) – species accounts and related documents. U.S. Fish and Wildlife Service, Washington, D.C. https://ecos.fws.gov/ecp0/profile/speciesProfile?sId=6315
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.
