Heracleum maximum

The leaves are very large, up to 40 cm (16 in) across, and divided into lobes.

The seeds are 8–12 mm (0.3–0.5 in) long and 5–8 mm (0.2–0.3 in) wide

Cow parsnip is a tall herbaceous plant reaching heights of over 2 m (7 ft). The genus name Heracleum (from Heracles) refers to the very large size of all parts of these plants.[6] Cow parsnip has the characteristic flower umbels of the carrot family (Apiaceae). The umbels are about 20 centimetres (8 in) across, flat-topped or rounded, and composed of small white flowers. Sometimes the outer flowers of the umbel are much larger than the inner ones. The leaves are very large, up to 40 cm (16 in) across, and divided into lobes. The stems are stout and succulent. The seeds are 8–12 mm (0.3–0.5 in) long and 5–8 mm (0.2–0.3 in) wide.[7]

It is commonly confused with Heracleum mantegazzianum (giant hogweed),[8] which is a much larger plant that typically has purplish spots on the stems, as well as more sharply serrated leaves.[9]

According to The Plant List and Plants of the World Online, Heracleum maximum is an accepted species name with no infraspecific taxa.[10][5] It is also accepted by the Database of Vascular Plants of Canada (VASCAN), referencing the in prep family treatment in the Flora of North America project.[2] Several synonyms of Heracleum maximum are listed at Plants of the World Online:[5]

On the other hand, Heracleum maximum is not recognized as an accepted name by either the Integrated Taxonomic Information System (ITIS) or the National Plant Germplasm System (NPGS).[11][12] According to ITIS and NPGS, both Heracleum maximum and Heracleum lanatum are synonyms for Heracleum sphondylium subsp. montanum.[11][12] These three names are often used interchangeably in the literature.

The classification given here follows The Plant List (which was last updated in 2013), that is, each of Heracleum maximum, Heracleum lanatum, and Heracleum sphondylium subsp. montanum is a distinct species.[10][13][14]

In Homer, Alaska

And the same spot in late winter, showing the white stalks of dead cow parsnip

Cow parsnip is distributed throughout most of the continental United States except the Gulf Coast and a few neighboring states. It occurs from sea level to elevations of about 2,700 metres (9,000 ft).[7] It is especially prevalent in Alaska, where it is often found growing amongst plants like devil's club, which is nearly identical to in size and somewhat similar in appearance, and monkshood, a very toxic flower. In Canada, it is found in every province and territory except Nunavut. It is listed as "Endangered" in Kentucky and "Special Concern" in Tennessee.[15]

The thick flower stems, coming into season in early summer, can be peeled and eaten cooked when young;[16] caution should be taken as the flowers resemble those of the extremely poisonous Cicuta maculata.[17] Cow parsnip is a valuable pasture plant for cows, sheep, and goats. It is also known to be important in the diets of numerous wild animals, especially bears, both grizzly and black.[4]

Indigenous North Americans have had a variety of uses for cow parsnip, often traveling long distances in the spring—50 miles (80 km) or more—to find the succulent plant shoots.[18] The young stems and leafstalks were peeled and usually eaten raw. In terms of taste, texture, and nutrients, the peeled stalks resembled celery, which gave rise to the common name "Indian celery". The natives were aware of the toxic effects of the plant, knowing that if the outer skin were not removed, one would get an "itchy mouth" or blistering skin.[18][19] Pregnant women were warned away from the flower bud stalks to prevent newborns from asphyxiating when crying.[18]

At least seven native groups in North America used the plant as a dermatological aid. It could be an ingredient in poultices applied to bruises or sores.[18][20] A poultice prepared from the roots of cow parsnip was applied to swellings, especially of the feet. The dried stems were used as drinking straws for the old or infirm, or made into flutes for children. An infusion of the flowers can be rubbed on the body to repel flies and mosquitoes. A yellow dye can be made from the roots.[20]

The plant contains furanocoumarins such as xanthotoxin,[21] angelicin, pimpinellin and isopimpinellin, isoimperatorin, bergapten and isobergapten, 6‐isopentenyloxyisobergapten, and sphondin.[22][23][21] In one study, the young leaves did not contain xanthotoxin, but older, senescing leaves contained "substantial amounts".[21] Some of these furanocoumarins found in cow parsnip are known to have antimicrobial[22][21] properties and are responsible for a rash producing erythematous vesicles (burn-like blisters) and hyperpigmentation that occurs after getting the clear sap onto one's skin.[19][21][24] They are photosensitive, with the rash occurring only after exposure to ultraviolet light.[21][24] Because of this, phytophotodermatitis causing skin blistering may occur after coming into contact with the sap on a sunny day.[24] The scars and pigmentation from these blisters caused by some Heracleum species can last for months or years.[22]

• Heracleum, the genus
• Other non-invasive Heracleum species: Heracleum sphondylium
• Tall invasive Heracleum species: Heracleum mantegazzianum, Heracleum sosnowskyi, and Heracleum persicum
• Other plants commonly mistaken for Heracleum maximum:[8] wild carrot, cow parsley, Angelica species, poison hemlock, wild parsnip

Wikimedia Commons has media related to Heracleum maximum.

• Jepson Manual species treatment
• Heracleum maximum in the CalPhotos Photo Database, University of California, Berkeley
• Images from the Connecticut Botanical Society
• Plants for a Future report on the species