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Stiff Cowbane, Pig-potato, Common Water-Dropwort - Oxypolis rigidior


Family: Apiaceae - Carrot family Genus Common Name: Cowbane Native Status: NativeDicot Perennial Herb
Oxypolis rigidior - Stiff Cowbane, Pig-potato, Common Water-Dropwort.
Oxypolis is a small genus of 4 species of North America. Recent reclassification moved 3 other species out of Oxypolis and into Tiedemannia. Two species of Oxypolis have relatively narrow distribution in the western United States - Oxypolis occidentalis being found in the United States only in California and Oregon and Oxypolis fendleri in the Four Corners states and Wyoming - while Oxypolis ternata is found in the wet pine savannas and sandhill seepages of the southeastern states of North and South Carolinas, Georgia, and Florida.

Oxypolis rigidior is by far the most widely distributed species in the genus, being found in 28 states along the east coast outside of New England, from New York south to Florida and west to Texas and Minnesota. It is a plant of wet areas such as streambanks, bogs, and seepages. Cowbane is toxic and should not be eaten.

Found in:
AL, AR, DC, DE, FL, GA, IA, IL, IN, KY, LA, MD, MI, MN, MO, MS, NC, NJ, NY, OH, OK, PA, SC, TN, TX, VA, VT, WI, WV
Oxypolis rigidior

Distribution of Oxypolis rigidior in the United States and Canada:
USDA Plants Distribution Map temporarily unavailable.
Blue=Native; Grey=Introduced

Map from USDA Plants Database:
USDA, NRCS. 2017. The PLANTS Database (http://plants.usda.gov, 13 Dec 2017). National Plant Data Team, Greensboro, NC 27401-4901 USA.

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Site: Bald River Road, Monroe County, TN Date: 2017-August-23Photographer: Gerald C. Williamson
Nikon D7000
Tamron SP 90MM f/2.8 AF Macro
Oxypolis rigidior grow to 2 to 4 feet tall. The inflorescence is a compound umbel - small umbellets (also known as umbellules) of flowers arranged in an umbel of rays arising from the terminal point of the peduncle. There may be multiple inflorescences on a single plant. The full inflorescence is up to about 5 inches across. Many (most? all?) species in Apiaceae carry their flowers in compound umbels, providing the alternate family name of Umbelliferae.
Oxypolis rigidior

Site: Bald River Road, Monroe County, TN Date: 2017-August-23Photographer: Gerald C Williamson
Nikon D7000
The umbellets are dome-shaped, almost ball-like clusters of tiny white flowers. Each umbellet (or umbellule) will contain in the vicinity of 20 pedicellatel flowers.
Click on the photo for a larger image
Oxypolis rigidior

Site: Bald River Road, Monroe County, TN Date: 2017-August-23Photographer: Gerald C Williamson
Nikon D7000
The individual flowers of Stiff Cowbane are about 1/8" across with 5 white petals and 5 white stamens surrounding the two-part gynoecium - a pair of green pistils; here the ovaries are darker green topped by the pair of pale green stigmas.
Click on the photo for a larger image
Oxypolis rigidior

Site: Indian Boundary Recreation Area, Monroe County, TN Date: 2017-August-23Photographer: Gerald C Williamson
Nikon D7000
The leaf and leaflets of Oxypolis rigidior are key to identifying the plant. The leaves are pinnately compound, with usually 7 to 11 leaflets, although occasionally they will have as few as 5 or as many as 13 leaflets. The leaflets may occasionally be entire (no teeth), or if they have teeth, they will be few and far between, and disposed toward the tip of the leaf. The leaflets are net-veined.
Click on the photo for a larger image
Oxypolis rigidior

Site: Bald River Road, Monroe County, TN Date: 2017-August-23Photographer: Gerald C Williamson
Nikon D7000
The green stems of of Oxypolis rigidior are terete, glabrous, and veined. The petioles of the leaves form a sheath around the stem and the branches that may sparingly occur in the plant, as well as on the flowering stalks that may arise from the leaf axil. I find it interesting that the leaf shown here only has 3 leaflets; fully developed leaves rarely have fewer than 5.
Click on the photo for a larger image
Oxypolis rigidior

References used for identification and information:

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All content except USDA Plants Database map Copyright Gerald C. Williamson 2017
Photographs Copyright owned by the named photographer