Americanized Giant Hogweed Gardens Weaken What They Do Not Kill

Summary: Americanized giant hogweed gardens, illegal in some parts of North America, kill native vegetation and weaken ecosystem diversity and human health.

giant hogweed plant, with pink cap to show scale: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org, CC BY 3.0 United States, via Forestry Images

The Alabama, California, Connecticut, Florida, Massachusetts, Minnesota, New Hampshire, North Carolina, Oregon, Pennsylvania, South Carolina, Vermont and Washington state and United States federal governments apply weed designations to Americanized giant hogweed gardens.

Designations as illegal, unwelcome weeds become North America-wide with legislation by Canada's provincial governments in Alberta, British Columbia, Ontario and Saskatchewan and by Mexico's federal government. Federal, provincial and state governments communicate concerns over challenges to native vegetation, plant diversity and stream bank diversity and over challenges to human health from toxins. Contact with concentrated toxic chemicals, called furanocoumarins, delivers nasty punches in purple-black blisters whose scars do not heal for six years and in long-term sunlight-activated sensitivities.

Giant hogweed, also called cartwheel flower, giant cow parsnip and scientifically Heracleum mantegazzianum (belonging to Hercules [and] Paolo Mantegazza), enchants few outside southwest Asia's Caucasus Mountains.

Biology fits lance-shaped embryonic leaves, called cotyledons, onto giant hogweed seedlings whose fling through two- to five-year life cycles finishes after the non-woody ornamental's one-time flowering.

The mature Apiaceae family member of carrot-related herbs gets dissolved hormones and nutrients from a pale yellow, toxic, 17.72- to 23.62-inch- (45- to 60-centimeter-) deep taproot. The crown union of the above-ground shoots, just below the stem base's sturdy, toxic sap-filled bristles, with the below-ground taproot often has a 5.91-inch (15-centimeter) diameter. A mature, 13.12- to 19.69-foot (4- to 6-meter) height is possible on hollow, purple- or red-splotched stems 1.18- to 3.94 inches (3 to 10 centimeters) across.

Alternate-positioned foliage juxtaposes compound basal and lower-stem leaves, each with three coarse-toothed, deep-cut leaflets, long stalks with sharp-pointed bumps and upper-stem leaves with three-lobed, tooth margins.

Basal foliage keeps a high profile, with leaves 3.28 feet (1 meter) in width and with rosettes 4.92 to 6.56 feet (1.5 to 2 meters) across.

Modified leaves called bracts look linear to oval around candelabra-like, flower-clustered, 11.81- to 31.49-inch- (30- to 80-centimeter-) across, 5.91- to 15.75-inch- (15- to 40-centimeter-) long umbels. Terminal umbels manage 50 to 150 rays and may be overtopped by up to eight lateral umbels and prefaced by lower, predominantly male flower-clustered, smaller umbels. White flowers need one two-styled pistil and five sepals if female and five 0.32- to 0.47-inch- (8- to 12-millimeter-) long petals and five stamens if male.

Two-sectioned, two- to four-seeded, 0.24- to 0.71-inch- (6- to 18-millimeter-) long, 0.16- to 0.39-inch- (4- to 10-millimeter-) wide fruits called schizocarps offer 100,000 giant hogweed seeds.

Dull or glossy, elliptical, oblong or oval, five-ribbed, flattened, 0.28- to 0.55-inch- (7- to 14-millimeter-) long, 0.19- to 0.43-inch- (5- to 11-millimeter-) wide, straw-yellow seeds persevere.

Seeds quit two- to 15-year viable dormancy after two-month-long temperatures at 35.6 to 39.2 degrees Fahrenheit (2 to 4 degrees Celsius) in the soil's top 1.97 inches (5 centimeters). Giant hogweed relatives such as poison hemlock, water hemlock, wild carrot and wild chervil receive similar designations as unwelcome weeds in Canada and the United States. Designations in six states serve to restrict bishop's goutweed in Connecticut, Massachusetts and Vermont, caraway in Colorado, spreading hedgeparsley in Washington and wild parsnip in Ohio.

Americanized giant hogweed gardens tend to kill native vegetation in the way of their North American tours and to weaken the health of gardeners and naturalists.

closeup of giant hogweed flowers; Musée de l'École de Nancy, Lorraine region, northeastern France; Sunday, June 17, 2007: Liné1, CC BY SA 3.0 Unported, via Wikimedia Commons

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

giant hogweed plant, with pink cap to show scale: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org, CC BY 3.0 United States, via Forestry Images @ http://www.forestryimages.org/browse/detail.cfm?imgnum=5452674

closeup of giant hogweed flowers; Musée de l'École de Nancy, Lorraine region, northeastern France; Sunday, June 17, 2007: Liné1, CC BY SA 3.0 Unported, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Heracleum_mantegazzianum_07_by_Line1.jpg

For further information:

Dickinson, Richard; and Royer, France. 2014. Weeds of North America. Chicago IL; London, England: The University of Chicago Press.

"Heracleum mantegazzianum Sommier & Levier." Tropicos® > Name Search.
Available @ http://www.tropicos.org/Name/1700135

Sommier, S. (Carlo Pietro Stefano); Émile Levier. April 1895. "Heracleum mantegazzianum nov. sp." Nuovo Giornale Botanico Italiano, nuova serie, vol. II, fascicolo II: 79-81.
Available via HathiTrust @ https://hdl.handle.net/2027/wu.89097505689?urlappend=%3Bseq=85

Weakley, Alan S.; Ludwig, J. Christopher; and Townsend, John F. 2012. Flora of Virginia. Edited by Bland Crowder. Fort Worth TX: BRIT Press, Botanical Research Institute of Texas.