One of the more dramatic plants you are likely to encounter in British Columbia the cow parsnip, Heracleum maximum. Come across a patch while on a nature walk and you are likely to hear exclamations of interest and wonderment, and someone is bound to observe that it looks like a giant Queen Anne’s Lace, the wild carrot, which it does. Someone will suggest, with some trepidation, that it might be giant hogweed. Good guess. It is quite similar to that plant, the true giant of the family, whose existence renders inaccurate the Latin name of cow parsnip, which is not so maximum after all.
The giant hogweed (also known as giant cow parsnip), Heracleum mantegazzianum, is native to the Caucasus Mountains of southwest Asia but has been ill-advisably introduced to other parts of the world, where it has taken over riverbanks and other wetland areas. Besides being a potential ecological nightmare, this plant is pure hazmat. It contains light-activated chemicals called furanocoumarins in its leaves, roots, stems, flowers and seeds, which can cause serious, burn-like dermatitis to skin that has been in contact with these plant parts and subsequently exposed to sunlight. Pigmented scars lasting several years can result. So watch out! Cue the Genesis…
Cow parsnip, on the other hand, is edible, and has been used as a green vegetable by almost every First Nations group along the north Pacific coast. Like hogweed, it favours moist areas such as stream banks, but can also be found in avalanche tracks, road cuts and the upper levels of beaches, from sea-level to sub-alpine.
How to tell them apart? For starters, if a plant is way taller than you are, it’s most likely giant hogweed. Cow parsnip is seldom more than 2 m tall; giant hogweed can reach 4 meters (although the size ranges overlap).
The stem-bases of giant hogweed can be more than 10 cm in diameter, although 3-8 cm is more common. Stems have diffuse or patchy purple pigmentation.
Giant hogweed stem and leaves. The basal (lowest) leaves of giant hogweed are crazily multi-lobed, and can be more than a metre across.
Cow parsnip stems and leaves.
Cow parsnip has green, somewhat hairy stems, 1-3 cm in diameter. The basal leaves are three-lobed, with each lobe bearing additional minor lobes. Upper leaves may be simpler, somewhat maple-like.
Cow parsnip occurs from Alaska to California and is found throughout British Columbia. In BC, Giant hogweed is known only from isolated localities on eastern Vancouver island and the Lower Mainland (Vancouver area). Most or all instances have origins in intentional plantings, likely meant to produce spectacular specimen plants. Pity the gardeners assigned to prune them.
If you want a big, leafy carrot-thing to accompany your water feature, go with cow parsnip. It’s spectacular in its own right, and a lot friendlier.
Reference: Page, N. 2004. Giant Hogweed, Heracleum mantegazzianum: a nasty invasive plant species in British Columbia. Menziesia 9(2): 1,5-8.