Peacock butterfly feeding on Hemp Agrimony

As summer reaches its end Hemp Agrimony, Eupatorium cannabinum, is coming towards the end of its flowering period. It is one of the glories of the summer, with frothy, pinkish flower clusters that appear from July to September and are often covered in insects, especially butterflies and hoverflies.

Hemp Agrimony (sometimes given a hyphen: Hemp-agrimony) is a native of the British Isles and other parts of Europe. It is a perennial herb and is found on base-enriched soils in a wide range of damp or wet habitats. Hemp Agrimony grows along the edges of ponds, lakes, canals and rivers and in fens, damp meadows and wet woodland. In some places it can also be found in dry woods, on hedge banks or on waste ground. It is more coastal further north but its range extends to Ireland and parts of Northern Scotland (see map).

A member of the Daisy family, Asteraceae, Hemp Agrimony is a bushy plant with flat-topped heads of numerous tiny pink flowers. (There are some great photographs of the plant on the Wildflower Finder website.) The flowers are followed by fluffy white seeds in autumn, which are spread by the wind. Hemp Agrimony’s trifoliate leaves, which have long, toothed leaflets, are attached in pairs to a reddish stem, which can grow between one and two metres tall. The name ‘Hemp Agrimony’ comes from the leaves’ resemblance to those of Hemp (Cannabis sativa). This resemblance is only superficial and Hemp Agrimony does not contain the cannabinoids that are found in Hemp (a member of a separate family, the Cannabaceae, which also contains Hops). Nonetheless, Flora Britannica relates the story of a raid on the Sussex Trust for Nature Headquarters by the Drugs Squad, because someone mistakenly thought the plant was Cannabis.

Hemp Agrimony has sometimes been used medicinally and the Modern Herbal and The Herbal Resource websites list uses including purifying the blood and treating jaundice, fevers and influenza. However, the plant contains pyrrolizidine alkaloids and these can cause liver damage, so beware! (Also see my post about Coltsfoot, Tussilago farfara, from March 2012.)

Eupatorium cannabinum has several other English names as well as Hemp Agrimony and Hemp-agrimony, including Raspberries and Cream (from the appearance of the flowers), Ague Weed (from its use in treating fevers), Holy Rope, St. John’s Herb, Sweet Mandulin, Sweet-Smelling Trefoil, Thoroughwort, Waterhemp and Water Maudlin.

If you have a damp and sunny or partly shaded area in your garden, Hemp Agrimony is worth growing. The related Eupatorium purpureum, from North America, known as Joe Pye Weed, has darker flowers and is also a good choice for gardens. It looks especially good with other late-flowering perennials, such as Rudbeckia and Helenium.

Purple Hairstreak butterflies usually stay up at tree top level, but this one has been tempted down by Hemp Agrimony.