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Oxypolis canbyi (Coult. & Rose) Fern.Canby Dropwort
Federal Protection: Listed Endangered
State Protection: Endangered
Global Rank: G2
State Rank: S2
Element Locations Tracked in Biotics: Yes
SWAP High Priority Species (SGCN): Yes
Element Occurrences (EOs) in Georgia: 22
Habitat Summary for element in Georgia: Cypress ponds and sloughs; wet savannas
Perennial herb forming colonies by long, thin underground stems (rhizomes). Stems are up to 5 feet (1.5 meters) tall, slender, erect, smooth, the lower portion purple, branching only near the top. Leaves are 8 - 12 inches (20 - 30 cm) long, alternate, slender, round in cross-section and tapering to a point, hollow except for cross-partitions; the lower leaves usually drop by flowering time or are underwater. Flowers are held in flat-topped clusters (umbels) containing 7 - 12 smaller, flat-topped clusters (umbelets). The flowers have 5 tiny, white petals that curve up and inward. Fruits are less than 0.25 inch (4 - 6 mm) long, flattened and broadly oblong, with corky ribs and broad, thickened wings, giving the fruit a flattened, rectangular shape in cross-section. All parts of the plant smell faintly of dill.
Common Dropwort (Oxypolis filiformis) occurs in similar habitats but it is a coarser plant, with thicker stems and leaves than Canby’s Dropwort. It retains its lower leaves while flowering, and each umbel contains 10 - 20 smaller umbelets. Mature fruits have narrow, thin wings with only a few corky ribs, giving them a spindle-shape in cross-section.
Savanna Cowbane (Oxypolis denticulata, Special Concern) occurs in wet pine savannas and bogs in the Coastal Plain. For more information, see: https://www.georgiabiodiversity.org/natels/profile?es_id=17485
Wetlands, such as cypress ponds and sloughs, Carolina bays, and wet savannas, with acidic, organic soils and fluctuating, though usually high, water levels; there is patchy or no canopy cover.
Canby’s Dropwort reproduces sexually by seed as well as asexually by the spread of rhizomes, sometimes forming extensive colonies. Canby’s Dropwort flowers are capable of both self- and cross-pollination. Some umbels contain only bisexual flowers while others have female flowers in the outer part of the umbel and male flowers in the inner. Because the stamens typically mature and shed pollen before the pistils become receptive, self-pollination rarely occurs; and, due to the isolation of the small, usually clonal populations, cross-pollination is also limited. As a result, sexual reproduction is uncommon in this species and most reproduction is by spread of rhizomes. Adults of the Black Swallowtail butterfly (Papilio polyxenes asterius) lay their eggs on Canby’s Dropwort stems (as well as on the stems of other plants in this genus); once hatched, the larvae (caterpillars) often chew through the stems just below the umbels, further limiting the chance of sexual reproduction. In some populations, as many as 17% of the Canby’s Dropwort stems were eaten through by butterfly larvae.
Surveys are best conducted during flowering (late June–August) and fruiting (August–October). Both flowers and fruits are useful for identification.
Coastal Plain of Georgia, South Carolina, North Carolina, Maryland, and Delaware.
Conversion of habitat to pine plantations and agriculture by ditching, draining, and filling wetlands; fire suppression in wetlands and surrounding woodlands; building firebreaks in transition areas between uplands and wetlands; lowering of water table by ground water withdrawal.
Oxypolis canbyi is ranked S2 by the Georgia Department of Natural Resources, indicating that it is imperiled in Georgia. It is listed as Endangered by the State of Georgia and the U.S. Fish and Wildlife Service. About 20 populations have been documented in Georgia, but only 14 have been confirmed in recent years. Only two occur on conservation lands.
Apply prescribed fire every 2 - 3 years and allow fire in uplands to burn into edges of ponds and Carolina bays; avoid placing firebreaks in transition zones between uplands and wetlands and ponds. Avoid ditching, draining, or altering hydrology of ponds, sloughs, and bays. Limit ground water withdrawal.
Chafin, L.G. 2007. Field guide to the rare plants of Georgia. State Botanical Garden of Georgia and University of Georgia Press, Athens.
Kral, R. 1983. A report on some rare, threatened, or endangered forest-related vascular plants of the South. Technical Publication R8-TP2. United States Forest Service, Atlanta.
Kral, R. 1981. Notes on some "quill-leaved" umbellifers. Sida 9(2): 124-134. https://www.jstor.org/stable/41966599?seq=1
NatureServe. 2019. Oxypolis canbyi comprehensive report. NatureServe Explorer. Arlington, Virginia. http://explorer.natureserve.org/servlet/NatureServe?searchName= Oxypolis+canbyi
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.
Tucker, A.O., N.H. Dill, T.D. Pizzolato, R. Kral. 1983. Nomenclature, distribution, chromosome numbers, and fruit morphology of Oxypolis canbyi and O. filiformis (Apiaceae). Systematic Botany 8: 299-304. https://www.jstor.org/stable/pdf/2418483.pdf?refreqid=excelsior%3Aa8873c307e16d51f658bffe17acbbd21
USFWS. 2018. Canby's Dropwort (Oxypolis canbyi) species profile and related documents. U.S. Fish and Wildlife Service. Washington, D.C. https://ecos.fws.gov/ecp0/profile/speciesProfile?sId=7738
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
L. Chafin, Jul. 2008: original account
K. Owers, Feb. 2010: added pictures
L. Chafin, Mar. 2020: updated original account