Hypericum perforatum – September 29th 2025 – St John’s-wort
Attribution: Prof. Dr. Thomé, Otto Wilhelm, Public domain, via Wikimedia Commons
The New Flora of the British Isles lists as many as 22 species and hybrids of Hypericum in Britain, some of them being rare and hard to distinguish, but this one is common and can be identified by holding it up to the light. With back-lighting, the leaves appear perforated as if with pin-pricks. How unusual. I have often wondered “why?”. We’ll return to that question later.
Hypericum has recently been placed in a Family of its own, the Hypericaceae. The two common native species in Britain are H. androsaemum (called Tutsan) and this week’s plant, H. perforatum, the Perforate St. John’s-wort.
The flowers measure about 1.5–2.5 cm across, with five petals anf five sepals. Image, Chris Jeffree.
Hypericum perforatum is a perennial plant up to 60 cm tall, flowering from June to September and shedding its seeds from August onwards. There can be as many as 15,000 seeds per plant. Some may remain dormant in the soil for many years, but most are likely to germinate in the following spring. The old shoots die back in autumn, but young shoots and buds remain green over winter.
Back-lit image of the leaf, showing veins, perforations and black dots. Image: Chis Jeffree.
It can be found in many open habitats. Grime et al (1988) say “Frequent on calcareous wasteland and limestone quarries, on both spoil and ledges in the quarry face itself…frequent on cinders and ballast beside railways”. We somtimes see it beside roads. Last week I found masses of it, still flowering in mid-September, on a newly cleared site in Girvan (South Ayrshire, Scotland). There were huge piles of stones from an ancient wall (held together with lime mortar), much rubble and many stones. I believe the land clearance earlier this year exposed buried seeds to light, triggering germination. Perhaps next year this place will be a superstore or caravan park, like much of the land nearby.
A cleared derelict site at Girvan (South Ayrshire) with young flowering plants. Clearing was done in early 2025, and the photographs are 26.09.25. Image: John Grace.
St. John’s-wort has a long history as a medicinal plant. One legend links the healing power to the perforations as follows: “in his anger about the extraordinary healing powers of the plant the devil is said to have attacked it with a needle and perforated it thousands of times”. It was supposed to drive away evil spirits and protect against witchcraft. One modern herbal mentions its use for treatment of sunburn, bruises, sores and minor injuries (Hensel 2008). I am not qualified to judge the claims made by herbal practitioners, but up-to-date, well-informed reports speak positively about one particular aspect of its traditional use: the 2022 article by the European Medicines Agency authorises it for “treatment of mild to moderate depressive episodes… short-term treatment of symptoms in mild depressive disorders”. Consistent with this article, I found several offers on Amazon.com for pills containing St. John’s-wort, including ‘Good Mood Tablets’. I like the idea, and Amazon’s users are mostly delighted with their purchases1.
This ‘worm’s eye view’ shows the black dots along the edges of the petals and on the leaves, as well as the parallel tubular glands on the petals (appearing grey). Image: Chris Jeffree.
Putting aside the legends of Devils and Witches, is there really a link between the ‘perforations’ and the medicinal power? The ‘perforations’ are not perforations at all, but glands. Each one is a spherical structure formed within the leaf, sandwiched in between the upper and lower epidermis, forming a translucent chamber filled with an oily substance. Images to show the arrangement of this structure may be found in the article by Curtis and Lersten (1990). The flat cells lining the chamber secrete various chemicals, presumable to ward off grazing animals and/or pathogenic fungi and bacteria. One of these is a red fluorescent pigment, probably unique to Hypericum, called hypericin. There are other glands which appear black; they can be either spherical or tubular and are seen on petals and other parts of the plant. These have not been studied as much as the translucent ones, but they too contain active ingredients.
Section of leaf to show the location and size of spherical chamber (x). From Curtis and Lersten (1990) Internal secretory structures in Hypericum (Clusiaceae): H. perforatum L. and H. balearicum L.” New Phytologist 114, 571-580.
It is well known that hypericin causes photosensitization when ingested by grazing animals including cattle, sheep, goats and horses (Crompton et al 1988). In sunlight, these animals are prone to sunburn and may have blistering of the muzzle, causing them to refuse food. Hypericin is a large molecule (C30H16O8), made up of conjoined benzene rings; it has considerable biological activity, potentially useful for treating depression, cancer, and coronavirus infections.
As well as hypericin (and closely related compounds) there are many essential oils2, most of which are sesquiterpenes. These are a class of diverse natural chemicals with anti-inflammatory and antimicrobial properties. Concentrations of active constituents in the overall chemical ‘cocktail’ are likely to vary with age of the plant and growing conditions.
Global distribution of Hypericum perforatum, from GBIF.
Hypericum perforatum now has a wide global distribution, having been transported by European settlers who regarded fondly it as a spiritual, magical or medicinal plant. It was introduced to North America as early as 1696, and it came to Australia and New Zealand in the middle of the 19th Century. In these countries it appears to be more vigorous than in Europe, becoming invasive if unchecked, and in as many as 20 countries they call it a ‘noxious weed’. In Australia for example it infests hillsides, roadsides, river banks, railways and pasture lands.
The name Hypericum comes from the Greek Hyper = above and Eikon = picture, referring to the tradition of hanging the plants above religious pictures to ward off evil. The link to St John refers to the habit of harvesting the plant on St John the Baptist’s day, 24th June. The other common species Hypericum androsaemum gets the name Tutsan from the French phrase ‘toute-saine’ which literally means ‘all-healthy’ referring to traditional medicinal uses.
Footnotes
1This is not intended as a recommendation, either by the author or by the Botanical Society of Scotland.
2The term ‘essential oil’ is sometimes misunderstood. ‘Essential’ refers to the essence of the plant and does not indicate that it is nutritionally essential in the human diet.
References consulted
Campbell MH (1985) Germination, emergence and seedling growth of Hypericum perforatum. Weed Research 25, 259-266.
Campbell MH and Delfosse ES (1984) The biology of Australian weeds 13. Hypericum perforatum J. Aust. Inst. Agric. Sci. 50, 63-73.
Crompton CN et al. (1988) The biology of Canadian weeds. 83. Hypericum perforatum L. Can. J. Plant Sci. 68, 149-162
Curtis JD and Lersten NR (1990) Internal secretory structures in Hypericum (Clusiaceae): H. perforatum L. and H. balearicum L.” New Phytologist 114, 571-580.
Hensel W (2008) .Medicinal Plants of Britain and Europe. A&C Black, London.
Pan, X-G et al. (2024) New polycyclic polyprenylated acylphloroglucinols with antidepressant activities from Hypericum perforatum L. Bioorganic Chemistry 151, 107657.
Stace CA (2014) New Flora of the British Isles, 4th edition. C&A Floristics.
Internet sites
click for bugwomanlondon
https://en.wikipedia.org/wiki/Hypericum_perforatum
©John Grace
