St John's-worts
What are they?
The bright yellow, five-petalled flowers with prominent stamens of St John's-worts are rather distinctive and set this group apart from other families of plants. The genus contains both woody and herbaceous perennials, with a number of species showing distinctive dark spots actually stalkless glands) on the leaves and flowers, while the leaves also show translucent marks when held up to the light. Some of these plants have been used medicinally in the past (hence the presence of the term 'wort'), while others are popular as showy and long-flowering garden ornamentals.
Where are they found?
There seems to be a St John's-wort for almost every habitat, so habitat choice can be a useful part of the identifcation process. Some favour acid wetlands, others prefer dry, chalky areas, while some are more typically generalists.
Identification
The St John's-worts are a fairly easy group to identify to family, but a little trickier to get to species. You should note whether the leaves have translucent marks (hold up to the light) or black gland spots, and check too for black glands on the sepals and even the petals. Length of the stamens relative to the petals is useful, as well as whether the stems are smooth or hairy and rounded or square.
Perforate St John's-wort Hypericum perforatum
Native. Our one plentiful species, found throughout the region in grassy places and sometimes forming extensive colonies in sunny, grassy places. Flowers June to September. Sepals, backs and edges of petals and leaf edges all with stalkless black glands. Leaves also with many translucent spots. Stems rounded with two small ridges.
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Square-stalked St John's-wort Hypericum tetrapterum
Native. Widespread in wet places in damp meadows, marshes and riversides. Flowers June to September. Sepals, petal and leaf edges sometimes with a few stalkless black glands or sometimes without. Leaves with a few translucent spots. Stems four-sided with winged corners.
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Slender St John's-wort Hypericum pulchrum
Native. A plant of acid soils so rather local in East Anglia and found on both sunny and shady banks and heathy places. Flowers June to August. Petals strongly red tinged on the back, especially in bud. Sepals and petals with stalked black glands along the margins. Early leaves ovate, but later stem leaves triangular, sometimes with overlapping bases. Stems rounded.
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Imperforate St John's-wort Hypericum maculatum
Native. Widely scattered but uncommon in damp, grassy places, often beside ditches or woodland tracksides. Flowers June to August. Sepals less than half the length of the petals. The petals and sepals both have black, stalkless glands but these tend to be short lines rather than rounded dots. Leaves without translucent spots. Stems weakly four-sided but not winged.
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Hairy St John's-wort Hypericum hirsutum
Native. Widespread on boulder clay through the middle of the region, becoming commoner on chalkier soils to the south and west. Typically found in wooded locations, especially older, species-rich woodland. Flowers July to August. Stalked black glands on sepals and occasionally on the pale yellow petals. Leaves strongly veined without translucent spots. Stems rounded and distinctly hairy.
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Marsh St John's-wort Hypericum elodes
Native. Rather rare in East Anglia and confined to good quality, acidic sphagnum bogs in East Suffolk and a handful of sites in Norfolk. Flowers June to September. A very distinctive species that forms creeping mats, sometimes extending out onto the surface of open pools. Leaves and stems with white hairs. Small, pale yellow flowers have red, glandular hairs on the sepal margins.
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Trailing St John's-wort Hypericum humifusum
Native. Quite widespread though rarely common on acidic, sandy soils in short grass on tracks and dry banks. Flowers June to September. A distinctive species that forms creeping mats. Leaves with translucent dots and often a few black glands. Sepals about 2/3 length of petals, both with just a few black glands. Stems hairless, rounded with two ridges.
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Olympic St John's-wort Hypericum olympicum
Introduced as a garden ornamental from SE Europe. Recorded from single sites in Norfolk and Cambridgeshire. Flowers June to August. Distinctive for its slender stems with small, glaucous-grey leaves and its large, overlapping sepals. Leaves have translucent dots but no black glands.
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Rose-of-Sharon Hypericum calycinum
Introduced as a garden ornamental from SE Europe. Commonly planted as an amenity groundcover plant and regularly spreading onto neighbouring roadsides, tracksides and into shady places. Flowers June to September. A low-growing plant that spreads vegetatively from underground stems. Flowers large (5-8cm across) and carried singly on unbranched stems. Leaves tough and evergreen.
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Common Tutsan Hypericum androsaemum
Native in western Britain but an introduction in East Anglia and spreading readily from bird-sown seeds. Common in shady churchyards, gardens and cemeteries and occasionally found naturalised in woodland. Flowers June to September. A woody, open-branched perennial to almost a metre in height. Leaves relatively large, semi-evergreen to deciduous. Flowers in branched heads and followed by conspicuous berries that change from green through red to black as they ripen.
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Tall Tutsan Hypericum x inodorum
A garden ornamental but may also occur as a natural hybrid in southern Europe. Occasionally planted in parks and amenity areas but only rarely spreading to the wider countryside. Flowers June to August. A well-branched shrub to 2 metres in height. Flowers 1.5-3cm across with stamens longer than the petals. Deciduous and with two-ridged stems. Fruits a hard capsule but turning red when ripe. The leaves and stem carry the unpleasant smell of Stinking Tutsan (one of its parents), though not as strongly. Intermediate between its parents, with the leaves and fruits similar to Common Tutsan and the flowers more like Stinking Tutsan.
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Stinking Tutsan Hypericum hircinum
Introduced as a garden ornamental from southern Europe. Occasionally planted but rarely spreading. Flowers May to August. A well-branched shrub to 1.5 metres in height. Flowers 2.5-4cm across with stamens much longer than the petals; sepals dropping early as the flowers mature. More or less deciduous with a few leaves overwintering on four-angled stems. Fruits a hard capsule not a berry. The whole plant has a strong and unpleasant smell. Unfortunately this plant has been allowed to aggressively colonise the north end of Holkham Park, due to misidentification as another species and a presumption that it is native!
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Hidcote Tutsan Hypericum x hidcoteense
A hybrid of garden origin that is popular and very widely planted. Occasionally found surviving from plantings on old garden sites or from discarded garden waste. Flowers May to August. A well-branched shrub to nearly two metres in height. Flowers large 3.5-8cm across with stamens only about half as long as the petals; sepals persistent. Semi-evergreen with leaves carried on rounded or only weakly four-angled stems. Fruits a hard capsule not a berry.
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