Giant Hogweed vs Wild Parsnip: White or Yellow?

Safety first. Do not touch either plant. Both have sap that can burn skin when it meets sunlight. Giant hogweed causes the more severe reaction, but wild parsnip is not a safe substitute. If sap gets on your skin, wash it off with soap and water as soon as possible and keep that area out of the sun for 48 hours. See a physician if a reaction starts. If sap gets in your eyes, rinse with water and seek medical care.

Giant hogweed vs wild parsnip: start with flower color

Flower color is the fastest check you can make from a distance. Giant hogweed has white flowers. Wild parsnip has yellow flowers. New York State DEC puts both plants in the same look-alike table and makes the color difference plain.

That matters because the two plants share a shape: both are tall carrot-family plants with umbrella-like flower heads and divided leaves. A yellow head is wild parsnip. A white head up to 2.5 feet wide is a hogweed problem.

Size: giant hogweed towers over wild parsnip

Giant hogweed is usually 7 to 14 feet tall, according to New York State DEC. Wild parsnip grows up to 5 feet tall, according to both New York State DEC and Wisconsin DNR.

Height alone is not enough. A young giant hogweed can be shorter than its mature size, and a wild parsnip in rich soil can be toward the top of its range. Use height to narrow the choice, then check the flowers and leaves.

Leaves: deeply cut or pinnate

Giant hogweed leaves are compound, lobed and deeply incised. New York State DEC gives a maximum width of about 5 feet. They look almost jagged, with deep cuts between the lobes.

Wild parsnip leaves are compound and pinnate. Wisconsin DNR describes the first-year rosette leaves as pinnately compound with 5 to 15 broad, oval to oblong leaflets. The stem leaves have 2 to 5 pairs of sharply toothed leaflets, and New York State DEC describes the foliage as often yellowish-green.

Do not part the foliage with your hands to compare leaves. Use a photo taken from a safe distance, or compare from the edge of the patch.

Stems: coarse hairs or grooves

Giant hogweed stems are 2 to 4 inches across, hollow and ridged. They have dark reddish-purple blotches, coarse white hairs, and a thick circle of hairs at the base of each leaf stalk. New York State DEC calls that hair collar one of the plant’s identifying features.

Wild parsnip stems are hollow, yellowish-green and grooved along their full length. They have no hairs or bristles. Wisconsin DNR describes the stem as stout, hollow and grooved, up to 5 feet tall.

Purple blotches point to giant hogweed, but they are not always obvious. Wild parsnip stems are yellowish-green and grooved, without the blotches. The hairs, the grooves and the flower color carry more weight than color alone.

The sap: both can burn skin

Giant hogweed sap contains chemicals called furanocoumarins. When sap on skin is exposed to sunlight and moisture, it causes phytophotodermatitis, a serious skin inflammation. New York State DEC says the reaction can start as soon as 15 minutes after contact, with painful blisters forming within 48 hours. Scars can last up to six years, though they usually last a few months, and the skin can stay sensitive to sunlight.

Wild parsnip sap contains the same class of chemicals. Wisconsin DNR warns that sap plus sunlight can cause severe rashes, blisters and skin discoloration. NC State Extension lists wild parsnip as having medium-severity poison characteristics, with contact dermatitis and light sensitivity.

That is why “it is only wild parsnip” is not permission to handle it bare-handed. Wear gloves, long sleeves and long pants if you have to work near either plant. Do not use a weed trimmer or brush cutter on giant hogweed; New York State DEC says sap can splash three to four feet when plants are cut or damaged.

If sap gets on someone’s skin and a rash, blistering or burn appears, or you are unsure what to do, call Poison Control at 1-800-222-1222 (free, confidential, 24 hours) or use poison.org. For trouble breathing or a severe reaction, call 911.

What to do if you find either plant

If you think it is giant hogweed: do not cut, mow or pull it. Photograph the whole plant, the stem, the leaves and the flowers from a safe distance. In New York, report it to the DEC Invasive Plant Information Line at 845-256-3111, through iMapInvasives, or through your local PRISM. Outside New York, send the photos and location to your state agriculture department or extension office and ask them to confirm it. Giant hogweed is a federally listed noxious weed.

If you think it is wild parsnip: keep away from the sap and keep children and pets out of the patch. Wisconsin DNR says to wear gloves, long sleeves and long pants when handling it. For a large stand, or one near a playground, trail or waterway, ask your extension office or local weed program about control. Do not mow a stand and then handle the cuttings with bare hands.

If sap reaches your skin, wash thoroughly with soap and water, keep the area covered and out of the sun for 48 hours, and see a physician if a reaction starts. New York State DEC gives the same first-aid steps for giant hogweed.

For the giant hogweed profile, see giant hogweed. For the native look-alike, see cow parsnip vs giant hogweed. For New York rules and reporting, see invasive plants in New York. For other pairs, see look-alikes, and for plant profiles by category, see plants.