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Hypericum perforatum L., Perforate St John's-wort

Account Summary

Native, rare or very occasional, probably under-recorded. Eurosiberian southern-temperate, but widely naturalised in both hemispheres.

1882; Stewart, S.A.; Carrick Td.

June to September.

Growth form and preferred habitats

This rhizomatous, much-branched, erect herbaceous perennial can reach 75 cm in height, although habitat factors often restrict its growth and typical plants rarely achieve more than 30 cm. Some taproots penetrate deeply in suitable soil, while other roots remain superficial. It overwinters as an underground rhizome. It is only very occasionally recorded in Fermanagh and in other parts of NW Ireland. Typically it is a herb of rather shallow, dry or well-drained, infertile, open or moderately disturbed, rocky calcareous grassland, wood margins, lakeshores and artificial habitats including quarries. It prefers warm ground and therefore tends to avoid shade and wet or strongly acidic soils (lower than about pH 5.0) (Grime et al. 1988). These particular environmental requirements naturally restrict the occurrence of this species to some extent in the prevailing climate of W & NW Ireland.

The presence of many translucent dots scattered over the leaf (best seen when the leaves are held up against the light) gives H. perforatum both its scientific name and its most frequent English common name. The glandular dots are oil sacs which extend almost the entire depth of the leaf blade from upper to lower epidermis. When bruised the leaves release an aromatic scent from the oil glands. The rosin-like smell and the stickiness of the oil on the many-flowered, branched inflorescence, gives the species an alternative name in Yorkshire and the USA, 'Rosin Rose' (Salisbury 1964, p. 209).

Variation and apomictic reproduction

H. perforatum is a very variable species in terms of its physical form, size, vigour and degree of 'weedy' behaviour. A number of varieties, subspecies or separate species have been recognised by European taxonomists (N.K.B. Robson, in: Tutin et al. 1968). The subdivision appears to be based mainly on leaf size and shape.

To a large extent, H. perforatum does not set seed in the normal sexual manner, ie meiosis (reduction division) to form haploid male and female gametes which fuse to form a diploid zygote embryo that develops into the next generation. Pollen formation is straightforward, the sex cell undergoing normal meiosis (reduction division), but the resultant pollen can sometimes be up to 30% sterile. In the formation of the female ovules, 97% of the time meiosis fails to occur and the embryo-sac chromosome complement remains unreduced. The ovaries containing the unreduced ovules require pollination, but not fertilisation, in order to set seed. In this way, the normal reproductive cycle is short-circuited.

The fact that H. perforatum reproduction is not entirely apomictic means we should describe it a 'facultative apomict' species (Crompton et al. 1988). The remaining 3% of ovules set seed normally after meiosis, pollination and fertilisation. Despite these reproductive abnormalities, flowers appear to form seed equally well either by cross-pollination or by selfing. This unusual pattern of sexual reproduction strongly suggests that H. perforatum has originated as the result of hybridisation, and one of the parent species very probably is the closely related H. maculatum subsp. maculatum Crantz (Imperforate St John's-wort) (Robson 1990).

In their critical Flora, Sell & Murrell (2018) regard H. perforatum as a species aggregate and they subdivide it into as many as four species. The three additional species are named: H. lineolatum Jord. (Narrow-leaved St John's-wort), H. densifolium P.D. Sell (Dense-leaved St John's-wort) and H. microphyllum Jord. (Small-leaved St John's-wort). All four of these forms or species are apomictic.

Flowering reproduction

The yellow flowers, around 2 cm in diameter, are borne in many-flowered branched cymes from June to September. The flower contains many stamens in three bunches or fascicles and the superior ovary is topped by three long styles that spread outwards between the stamens. Although the rather showy flowers do not contain any nectar, they attract many kinds of insect visitors that collect the abundant pollen. As the flower ages, the pollen-covered anthers bend inwards and make contact with the stigmas to achieve self-pollination, although as mentioned above, almost all reproduction in this species is apomictic and agamospermous, so that seed set is automatic after pollination, without any actual fertilisation taking place (Proctor et al. 1996). However, since pollination is a necessary trigger for seed development in agamospermous species, this phenomenon is not easily detected. It is thus possible that agamospermy may occur in many other species, and be much more widespread than we know about at present.

All the seeds produced by agamospermy will usually be genetically identical to the parent species (apart from rare mutations), so they are effectively a clone formed and dispersed by seeds (Proctor et al. 1996).

Seed production, dispersal and longevity

An average-sized plant produces about 360 seed capsules and has a seed output of c. 30,000 per year. The seeds are the heaviest of any British terrestrial species, weighing 0.0001 gm (Salisbury 1942). The seed capsule ripens and splits but there is no specialised seed dispersal mechanism. It is imagined that the seed, which has a somewhat gelatinous seed-coat, is merely blown by wind, carried on animal coats or flushed along by rainwater. The species can sometimes be found growing on walls at some height (Ridley 1930, p. 29), and in areas like California where it has become a major, widespread weed, the initial infestations appeared to often reflect animal movement (Crompton et al. 1988). Although some seed is only transient, other samples can survive and germinate after more than 45 years burial in soil (Thompson et al. 1997). Seed germinates readily in the spring after production.

Vegetative reproduction

H. perforatum plants also reproduce very freely by vegetative means. Even the finest of the more superficial horizontal roots can produce adventitious shoots. Animal browsing or any other check to aerial shoot growth stimulates profuse propagation by this means. This allows the species to extend in relatively dense vegetation, whereas seedlings are restricted to more open, better illuminated conditions (Salisbury 1942).

Weediness

In Britain & Ireland, H. perforatum essentially is a poorly competitive, but stress-tolerant species, rather than a successful weedy pioneer coloniser of disturbed, open habitats. Grime et al (1988) described it as being intermediate between two of their categories: competitive-ruderal and their so-called intermediate C-S-R strategist. In western N America and in Australia, however, a taller and more vigorous form of the species has been introduced, or has developed, and there it has become a serious economic weed of rangelands, poorly managed pastures, roadsides, waste places, forest clearings and other non-arable sites (Crompton et al. 1988).

Toxicity

All members of the genus Hypericum contain a poisonous red, fluorescent glycoside pigment called hypericin. It is associated with the visible black glands that occur on the petals, leaves and stems. Hypericin is a polyphenolic compound structurally similar to Fagopyrin, the photosensitising agent found in buckwheat (Fagopyrum esculentum). Hypericin has been found to have antiviral and antidepressant properties. Animals eating plants containing hypericin may develop lesions on unpigmented skin exposed to bright sunlight (ie photosensitisation occurs). This is most likely to occur on hairless areas, such as eyelids, muzzles and udders. The skin reaction can take one to two weeks to develop in sheep, cows, pigs and horses, and established lesions are slow to heal, perhaps taking months.

Lesions cause the animals to rub and scratch and open lesions can become scabbed and infected. Other symptoms reported in horses include loss of appetite, diarrhoea, debility, staggering and even coma. Post-mortem examination of affected rabbits showed liver and kidney damage had occurred. Animals can recover, but once affected by photosensitisation, the condition more quickly reappears after further consumption of the pigment (Cooper & Johnson 1998).

Other toxins present in Hypericum include a polyphenolic flavonoid, called hyperoside, plus tannins and carotenes. Given adequate forage, most livestock avoid H. perforatum, although significant grazing may occur when plants are young and succulent. Mild poisoning reduces livestock performance, but the major significance of H. perforatum on N American rangelands, where it is an aggressive introduced alien weed, is that it reduces the carrying capacity of the land, rather than being a dangerously poisonous plant (Crompton et al. 1988).

Fossil record

There is only a very meagre fossil record of three separate stages for H. perforatum listed by Godwin (1975); one (rather tentative) seed record from the Late Bronze Age, one from the Roman era and one from the much earlier than the present (Ipswichian) interglacial.

Fermanagh occurrence

There are records of H. perforatum in the Fermanagh Flora Database from a total of 13 tetrads (2.5%), nine of which have post-1975 records. As the distribution map indicates, it is very thinly scattered around Lough Erne and on the western limestones.

The comparative rarity of recent H. perforatum records in Fermanagh suggests that it is overlooked to some extent or mistakenly identified as another Hypericum species. Five Fermanagh records are pre-1955 and the only records made by Meikle and his co-workers are from two quarries: Silverhill Quarry on the outskirts of Enniskillen (recorded 1953) and E.N. Carrothers's record of the same year from Clonmackan Quarry in the far SE of the county, near Clones town.

H. perforatum is distinguished from H. tetrapterum (Square-stalked St John's-wort) (the species in Ireland most like it) by its cylindrical as opposed to four-angled stem, which does, however, have two raised lines or ridges on opposite sides. In addition, Perforate St John's-wort has black streaks on some of the petals and leaves with intramarginal black or dark glands beneath. These features, plus variable quantities of the translucent leaf oil glands, separate H. perforatum from all Britain & Ireland species except H. humifusum and forms of the rare H. linariifolium (Toadflax-leaved St John's-wort), which anyway does not occur in Ireland (Robson 1990).

A considerable number of the very much more numerous H. tetrapterum records in Fermanagh are from rather drier, shaded, more ruderal habitats than might normally be the case for this species in other parts of these islands, eg on cliffs, in quarries and on roadsides. Some confusion may therefore exist between these two species and conceivably this might also involve H. maculatum (Imperforate St John's-wort), which is equally seldom found in Fermanagh (see below).

Irish and British occurrence

In Ireland, apart from the western limestones of the Burren, Co Clare (H9), E Connemara (H16 or H17?) and the Ben Bulbin mountains in Co Sligo (H28) and Co Leitrim (H29), H. perforatum has a quite definite eastern predominance, reflecting lower rainfall and less acidic soils. In Britain, it is much more widespread in lowland southern England and Wales than in Scotland, where it becomes rare N of the Solway Firth (Preston et al. 2002).

European and world occurrence

Abroad, a larger and very much more aggressively invasive form of this species is a major pasture weed in temperate areas of N America, Australia and New Zealand. Mowing and over-grazing reduced the very large, facultative apomictic seed production of the species, but promoted vegetative reproduction of fresh shoots from shallow, spreading roots and the rhizome. Rather successful biological control, however, has been achieved using chrysomelid beetles (Burdon & Marshall 1981; Crompton et al. 1988).

Uses

In herbal medicine, St John's Wort was used to treat all forms of pulmonary complaints, bladder troubles, dysentery, diarrhoea, worms, hysteria, nervous depression, bleeding and jaundice. In children, a drink of tea made with the leaves was used before bed to treat or prevent bed-wetting (Grieve 1931).

The main use of St John's Wort was as a white magic token, active against the powers of evil, and linked to St John the Baptist through his annual Saint's Day in the Christian calendar (24 June), when the plant was generally in flower. There are a number of folk traditions associated with the virtues of the plant, which involved lighting fires and smoking the leaves to further purify and strengthen their magical and medicinal powers. They were used to protect stables, cow-stalls, horses, animals or men against elves, devils, witchcraft, sickness and all evils. The plant is sometimes called an 'elf-chaser' or a 'devil-chaser', eg in France (chasse-diable). Undoubtedly some of this belief is a hangover from pre-Christian pagan times when similar ceremonies were invoked to protect the harvest, farm animals and people from storms, fires and devils.

The perforations observed in the leaves (the glandular dots), also became a 'signature' of wounds, reinforcing the signature of the red juice squeezed from the fresh stems and leaves, which is likened to the blood of St John at his beheading (Grigson 1987).

Names

There appears to be some confusion as to the origin and derivation of the genus name 'Hypericum'. The Classical Greek form of the name is 'hypereikon', and it was used by Dioscorides (a medic in the Roman army) for an unknown medicinal herb. Differing spellings and pronunciations occur: eg Gilbert-Carter (1964) says that in England the 'i' is wrongly treated as short. Some derive the name from the Greek 'hyper', meaning 'over or above', and 'ereike', 'a heath', possibly referring to the natural habitat of some species in the genus (Johnson & Smith 1946).

Another suggestion is that the second element of the name derives from 'eikon', meaning 'a picture', and thus 'Hypericum' means 'over (or above) a picture', which might refer to the belief in the magic properties of the plant, which was supposed to have power to dispel evil spirits, and is why the Devil pierced the leaves with a needle, ie a reference to the translucent glands which when the leaf is viewed against the light, make it look pierced with multiple pinholes. The flowers of some Hypericum species were therefore placed above religious images or shrines, to ward off evil at the ancient midsummer festival of Walpurgisnacht, which later became the feast of St John (24 June), when several species of the genus are in flower, and hence the origin of the name 'St John's-wort' (Stearn 1972; Gledhill 1985).

The Latin specific epithet 'perforatum' means 'pierced', or 'apparently pierced with small round holes' (Gledhill 1985), an obvious reference to the transparent oil glands in the leaves.

Seven English common names are listed by Grigson (1987), including two from North America where the species is a widespread and significant weed; 'Amber' and, as mentioned above, 'Rosin Rose'. The name 'Amber' is said to derive from the scent given off by the dried leaves, which is reminiscent of ambergris (Grigson 1987). Two English names refer to the leaves being used to dress and heal wounds, 'Balm of the Warrior's Wound' and 'Touch and Heal' (Grigson 1987). In Wales, the plant was called 'Mary's Ladder' or 'Christ's Ladder', possibly a reference to the opposite leaves and its devil chasing properties. Similar traditions and names occur in an Irish context, with the Virgin Mary, St Colum Cille and St Columba linked to the plant. It was sometimes worn under the left armpit to ward off evil spirits and death (Grigson 1987).

Threats

None.