- Heracleum mantegazzianum is a herbaceous biennial or monocarpic perennial that can grow up to 15-20 ft. (4.3-5.8 m) in height. The stem is hollow and usually blotched with purple. Both the leaf stalks and stem produce pustulate bristles. The stem can be 2-4 in. (4.8-9.6 cm) in diameter.
- The leaves are ternate or ternate-pinnate with pinnately lobed lateral segments. They can be up to 9.8 ft. (3 m) in breadth.
- Heracleum mantegazzianum flowers from June-July. The inflorescence has many white florets (with petals about 0.4 in. [1 cm]) that form a flat-topped umbel. Each inflorescence can have a diameter of up to 2.5 ft. (0.72 m).
- The fruits are dry and elliptic, measuring 0.3-0.4 in. (8-11 mm) long and 0.25-0.3 in. (6-8 mm) wide. The fruits have brown resin canals that can be up to 0.04 in. (1 mm) in diameter.
- Ecological Threat
- Heracleum mantegazzianum can outcompete species for habitat, especially in riparian zones, and it may cause increased soil erosion. This plant is on the federal noxious weed list because of its poisonous sap. This sap makes skin very sensitive to UV radiation, causing blistering and severe burns. Caution should be taken when handling this weed. Removing it manually becomes very difficult because of the danger caused by its sap.
Gucker, Corey L. 2009. Heracleum mantegazzianum. In: Fire Effects Information System, U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory 
Global Invasive Species Database. 2011. Invasive Species Specialist Group (ISSG) of the IUCN Species Survival Commission 
National Park Service, National Capital Region Exotic Plant Management Team, Washington, DC 
King County Department of Natural Resources and Parks Water and Land Resources Division 
Oregon Department of Agriculture Plant Programs, Noxious Weed Control 
Washington State Noxious Weed Control Board 
NOBANIS - Invasive Alien Species Fact Sheet 
Invasive Plant Atlas of New England (IPANE) 
Texas Invasive Plant and Pest Council 
USDA NRCS PLANTS 
USDA ARS GRIN 
Images from Bugwood.org