Issue 5, May 28, 2013

Is It Giant Hogweed?

Giant Hogweed ( is an invasive, exotic plant that has been found in a couple of locations in Illinois. As the summer season quickly approaches, the inquiries I receive about possible giant hogweed sightings begin to increase. Often, this invasive is confused with a very similar looking cow parsnip.

Giant Hogweed

As indicated by its name, this biennial or short-lived perennial can grow between 10 and 15 feet tall.  It has enormous compound leaves, up to 5 ft wide on the bottom sets, with 3 deeply incised leaflets. Thick stems are from 2 to 4 in thick, hollow and covered in purple blotches and course white hairs.  The easiest stage of identification of giant hogweed is in its flowering stage.  Numerous small white flowers are born in June or July in large flat-topped umbels up to 2½ ft across.  After the flowers produce their seeds by late-summer, the plant dies back to the thick taproot.  Its stem may persist throughout the winter.  

Giant Hogweed

Giant Hogweed belongs in the carrot or parsley family (Apiaceae). It has several look-a-likes ( including cow parsnip (Heracleum lanatum), angelica (Angelica atropurpurea), and poison hemlock (Conium maculatum -) all common plants in Illinois.  Although many of these plants may look like giant hogweed at first glance, none of them get to be as large or have its exaggerated characteristics.

In addition to being an invasive weed that can quickly overtake an area, giant hogweed can be harmful to humans.  It produces a clear, watery sap that is capable of causing photodermatitis – a sensitivity of the skin to sunlight. The sap produces painful, burning blisters or even painless red blotches that may turn purple over time. It is very important to wear gloves when handling this plant and to avoid the smoke if this plant is being burned nearby.

It is believed that giant hogweed made its way into the United States as an ornamental or was brought into the country for its fruit which is used as a spice in Iranian cooking. Undoubtedly, its unique stature and appearance has enticed gardeners to cultivate this plant. However, due to its size and rapid growth, giant hogweed readily out-competes many native plants. This perennial can survive in a variety of areas, but is common along roadsides, right-of-ways, railroads, vacant lots, streams, and rivers. Once established in an area, it can create a significant decline in biodiversity, increase soil erosion along riverbanks, and is difficult to eradicate. In addition, it often grows in wet areas, and can be considered an invasive freshwater weed. 

Giant hogweed is still rare in Illinois.

While visitors in natural areas are unlikely to encounter this plant, it never hurts to keep a watchful eye for this and other invasive plants.

For more information, stop by the Illinois CAPS blog ( for all the latest news on invasive pests in Illinois. (Kelly Estes)

Kelly Estes

Return to table of contents