Hierochloe odorata (sweet grass)
Hierochloe odorata, in Swinoujscie, NW Poland (Photo: Licensed under CC BY 3.0)
Hierochloe odorata (L.) P.Beauv.
sweet grass, holy grass, vanilla sweetgrass
Not assessed according to IUCN Red List criteria, but considered to be rare in Britain.
Wetlands, mountain slopes, floodplains, marshes and roadsides.
Strewn on church floors, burned as incense, basketry, local medicine, distilled beverages, ceremonial.
About this species
Hierochloe odorata is a member of the grass family (Poaceae). It is also known by the alternative name Anthoxanthum nitens, as used in the Flora of China and Flora of North America. The common name, sweet grass, refers to the fragrance emitted when fresh plants are crushed or burned to release the vanilla-scented compound coumarin, which it contains. The common name holy grass relates to its use in church festivals by early Europeans.
Anthoxanthum nitens (Weber) Y. Schouten & Veldk.
Geography and distribution
Native to Europe, Asia and North America, Hierochloe odorata is also widely naturalised. In North America it grows along the eastern coast from Labrador to New England.
Overview: Hierochloe odorata is a perennial, hairless or sparsely hairy, tufted plant with slender, creeping underground stems (rhizomes) and grows up to 55 cm tall.
Leaves: The aromatic leaf blades are 18–30 cm long and 0.04–0.10 cm wide. The edges of the leaf blades are slightly rough.
Flowers: The flowering parts are held in an open panicle (branched flowering structure), which is 4–11 cm long. The fertile spikelets (structures within which the flowers are held) are borne on hairless stems (pedicels) 2–4 mm long. The spikelets are composed of two sterile florets and one fertile floret.
Fruits: The fruit is a small, dry, thin-walled fruit with a single seed fused to the ovary wall (this fused product found in most grass species is termed a caryopsis).
Sweet grass has been used by Native Americans as incense, medicine for colds, analgesic and insecticide and in basketry; they also soaked it in water and used the infusion to wash their hair, skin and eyes.
Strewn on church floors by early Europeans, sweet grass was in some places dedicated to the Virgin Mary. Hierochloe odorata has also been used as an ingredient in strong alcoholic drinks in Eastern Europe. The Swedish botanist Carl Linnaeus reported that it was sold in Sweden to be hung over beds to induce sleep.
The distinctive, sweet scent of H. odorata is due to the presence of the chemical compound coumarin, which is also used to manufacture warfarin, used as a drug in surgery to prevent blood clotting and also as a rat poison.
Mouldy hay containing Hierochloe odorata should not be fed to cattle as Aspergillus species (fungi) turn coumarin into dicoumarol, which induces vitamin K deficiency and makes wounded animals more susceptible to bleeding.
Millennium Seed Bank: Saving seeds
The Millennium Seed Bank Partnership aims to save plant life worldwide, focusing on plants under threat and those of most use in the future. Seeds are dried, packaged and stored at a sub-zero temperature in our seed bank vault.
There are six collections of Hierochloe odorata held in Kew’s Millennium Seed Bank based at Wakehurst in West Sussex.
This species at Kew
Hierochloe odorata can be seen growing in the Grass Garden at Kew.
Pressed and dried specimens of sweet grass are held in Kew’s Herbarium, where they are available to researchers by appointment.
A specimen of Hierochloe odorata is held in Kew’s Economic Botany Collection in the Sir Joseph Banks Building, where it is available to researchers by appointment.
Kew at the British Museum - North American Landscape
Sweet grass (Hierochloe odorata) was one of the 12 star plants featured in the 2012 North American Landscape - the fifth in the series created by Kew for the British Museum’s West Lawn.
North American plants have global ecological and economic importance and have been utilised by native peoples for thousands of years. Many were introduced to Europe following the colonisation of North America in the early 1600s. Grown for their medicinal uses, as food crops and for other economic purposes, some species have also become familiar ornamental garden plants.
The landscape was designed to evolve throughout the seasons - from a carpet of colourful daisies in the summer to spectacular orange and red maple leaves in the autumn. Other plantings included cypress, echinacea and carnivorous pitcher plants.
Allred, K. W. & Barkworth, M. E. (eds) (2007). Anthoxanthum L. In: Flora of North America Volume 24. (Accessed 16 April 2012). Available online.
Clayton, W. D., Vorontsova, M. S., Harman, K. T. & Williamson, H. (2006 onwards). GrassBase - The Online World Grass Flora. (Accessed 10 April 2012). Available online.
Cope, T. & Gray, A. (2009). Grasses of the British Isles (BSBI Handbook No. 13). Botanical Society of the British Isles.
Mabberley, D. J. (2008). Mabberley’s Plant-book: a Portable Dictionary of Plants, their Classification and Uses. 3rd edition. Cambridge University Press, Cambridge.
World Checklist of Selected Plant Families (2010). The Board of Trustees of the Royal Botanic Gardens, Kew. (Accessed 10 April 2012). Available online.
Kew Science Editor: Emma Tredwell
Kew contributors: Maria Vorontsova
Copyediting: Emma Tredwell
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