A Guide to Britain's Rarest Plants

A Guide to Britain's Rarest Plants

by Christopher Dixon


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For centuries, botanists have been drawn to the rarest species, sometimes with dire consequences for the species' survival. In this book, Great Britain's rarest flowering plants are discussed in turn, including the stories behind their discovery, the reasons for their rarity, and the work being done to save them from dying out. It is hoped that it will help to throw light on some of the species that normally gain little attention, and foster an appreciation of our most threatened plants. This guide describes 66 native species of plants that have the most narrowly restricted ranges in Great Britain. These range from continental, warmth-loving species in the south of England to those found only on the highest Scottish mountains. Each species is shown together with its habitat to allow the reader to better understand the ecological context. Other scarce plants in the same area are indicated.

Product Details

ISBN-13: 9781784271466
Publisher: Pelagic Publishing
Publication date: 09/29/2017
Pages: 160
Product dimensions: 5.50(w) x 8.40(h) x 0.40(d)

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Creeping marshwort

Apium repens

Creeping marshwort is a low-growing herb in the same family as carrots, parsnips, parsley and celery, with tiny white flowers less than 2 mm across. It is closely related to celery, which grows wild in many coastal parts of England and Wales. It is even more closely related to fool's water-cress, Apium nodiflorum, which is usually a medium-sized plant, but can adopt a low-growing habit when it is heavily grazed, and can occur alongside creeping marshwort. The two can even interbreed to produce a hybrid. The main flowers-talk of creeping marshwort is longer than the secondary stalks, and the segments of each compound leaf are not noticeably longer than they are wide, both of which separate creeping marshwort even from short forms of fool's watercress.

Creeping marshwort is widespread, but not common, in Central and Southern Europe. In Britain, it is restricted to a few sites on the flood plains of the River Thames around Oxford, chiefly the ancient Port Meadow, where it was first found by the botanist John Sibthorp in 1794. These sites are often covered with water for long periods over the winter, and are heavily grazed by cattle and horses. As well as reproducing via seeds, creeping marshwort can spread vegetatively, with pieces of the plant floating on the floodwaters to find new habitat downstream.

A population of creeping marshwort has been introduced further downstream, although a proposed new channel that would reduce the risk of flooding in Oxford may require that population to be re-transplanted.


At the northern end of Port Meadow lie the ruins of Godstow Abbey, a former Benedictine nunnery. The nuns' herb-garden included birthwort, Aristolochia clematitis, which survives in the grounds of the abbey.

Alpine rock-cress

Arabis alpina

Alpine rock-cress is a mat-forming perennial plant that produces flowering stalks up to 40 cm (16 in) tall. It is classified in the same family as mustard, cress and cabbages – Brassicaceae. This family also includes a number of similar plants, and Alpine rock-cress can be told apart from its relatives only by a combination of several factors.

Alpine rock-cress has an arctic–alpine distribution, meaning that it is found at high latitudes in Scandinavia and elsewhere, and also in the similar climate of high mountains further south, including the Alps and the Pyrenees, but not in the areas in between. In Britain, it sometimes appears as a garden escape, but occurs natively only on the Isle of Skye.

Alpine rock-cress was discovered on Skye by Henry Chichester Hart, a colourful Irishman of independent means. Hart was an indefatigable field botanist, and happy to explore areas that were too difficult for almost anyone else. (He once bet a friend that he could walk the 69 miles – 111 km – from a tram stop in Dublin to the highest point of the Wicklow Mountains and back in a day; he won the bet.) This may be why he was the first to come across Alpine rockcress, given the steepness of the Black Cuillin range, where it grows at altitudes of 820–850 m (2,700–2,800 ft). The plants' precise locations are kept secret to save the population from harm. The extreme conditions of the Cuillin also hinder research into Alpine rock-cress, including tasks as simple as surveying the population size. Plants cultivated from the native population were re-introduced in 1975 in an attempt to bolster the population. In 1993, only three colonies were found, totalling 83 plants, and it is not known how the species has fared since.


Another Arctic plant, Iceland purslane (Koenigia islandica) from the dock family, occurs on the Trotternish peninsula of Skye as well as in some locations on Mull. It is very inconspicuous, and was not noticed in Britain until 1934.

Bristol rock-cress

Arabis scabra

Bristol rock-cress is closely related to Alpine rock-cress, Arabis alpina(p. 8), and is similar in appearance, although it forms compact tufts up to 25 cm (10 in) high instead of sprawling mats, and has shiny leaves with a sparse covering of thick bristles. It grows on open parts of rocky limestone slopes, and is readily smothered by competition. Each stem produces up to a dozen flowers, each 5–6 mm in diameter.

In the wild, Bristol rock-cress grows in the mountains of northern Spain and southern France – just extending over the border into Switzerland near Geneva – and at one site in Britain. That site is the Avon Gorge, where it was first found in 1686 by James Newton, assistant to the parson–naturalist John Ray, on St. Vincent's Rock – a site now better known as the foundation for the Clifton Suspension Bridge. Bristol rockcress grows chiefly on south-facing cliffs on either side of the River Avon, with smaller populations in quarries further downstream at Shirehampton. The populations by the bridge may have been briefly harmed by toxic heavy metals that were present in the copper slag used to shot-blast the bridge in 1995. A greater threat to the plant's continued survival may come indirectly from the road at the bottom of the gorge. In order to prevent rock-falls onto the road, strong nets have been strung across some of the slopes, trapping leaf-litter and allowing more vigorous plants to grow and outcompete the rather retiring Bristol rock-cress.

Bristol rock-cress has been introduced to similar sites nearby, but few of the populations have survived. One exception is a population at Combwich on the tidal reaches of the River Parrett in Somerset.


The Avon Gorge contains a number of rare species, including honewort (Trinia glauca) and several endemic or near-endemic whitebeam microspecies (Sorbus leighensis, S. eminentiformis, S. whiteana,S. wilmottiana and S. bristoliensis).

Norwegian mugwort

Artemisia norvegica

Norwegian mugwort is a small herb related to other mugworts and wormwoods, in the tremendously diverse daisy or sunflower family. The family relationship becomes clear when you examine the tiny drooping flower-heads, which resemble miniature sunflowers. It differs from other Artemisia species in its tiny size – only reaching 8 cm (c. 3 in) tall – and by its small number of flower-heads, typically only 1 or 2 per stem.

Norwegian mugwort grows in the northern Ural Mountains of Russia, in Norway, and in western Scotland. A closely related species (sometimes considered part of the same species) occurs in western North America and the Russian Far East. The Scottish populations are restricted to three mountains around Ullapool, where they grow along the high ridges above 700 m (2,300 ft). The first of these was found by the historian Sir Christopher Cox in 1950, the year he was knighted for services to education. Despite being such a recent discovery, the Scottish plants are unlikely to be a recent arrival, as they differ consistently from plants in the Urals and Norway by their shorter stature and less divided leaves. They have even been recognised as a separate variety, Artemisia norvegica var. scotica. Even such a seemingly small amount of evolution is likely to have taken hundreds or thousands of years. The fact that the Scottish populations grow so high up on the mountains also means that they will struggle to cope with climatic warming, because there is nowhere higher that they could migrate to in order to reach colder conditions. Indeed, they may already be struggling; it is reported that the plants rarely produce much viable seed.


Dactylorhiza incarnata subsp. cruenta, a subspecies of the early marsh orchid (sometimes treated as a separate species, Dactylorhiza cruenta) grows in the mires east of Lochinver.

Pedunculate sea-purslane

Atriplex pedunculata

Pedunculate sea-purslane is a shrubby, mealy plant that grows up to 30 cm (12 in) tall. It is classified in the family Amaranthaceae (formerly Chenopodiaceae), and is related to the much more widespread sea-purslane (Atriplex portulacoides), and more distantly to the oraches, goosefoots, spinach and beet. It can be immediately told apart from all its British relatives by its long-stalked fruits with two conspicuous bulges on the sides, a bit like the fruits of shepherd's purse, Capsella bursa-pastoris.

Worldwide, pedunculate sea-purslane is found in coastal areas from the Gulf of Bothnia to France, as well as around the Black Sea and at saline sites inland. In the past, it has occurred at sites from Lincolnshire to Kent, but was not found anywhere in Britain from 1938 to 1987, when a new population was discovered in southern Essex. Pedunculate sea-purslane is most abundant around the coasts of Denmark, and it has been speculated that it was unwittingly reintroduced to Britain by migratory brent geese.

The abundance of pedunculate sea-purslane is known to vary wildly from one year to the next, making local extinction a very real risk if few seeds are produced one year, or fail to settle in suitable positions. To improve its chances of persisting in the longer term, pedunculate sea-purslane has therefore been introduced to other sites in the area, including some on military land, where it can be protected more easily. It could also reappear at any time at any suitable sites along England's east coast that are visited by migrating geese.


Saltmarsh goosefoot, Chenopodium chenopodioides, is largely restricted in Britain to the drier parts of salt-marshes the Thames Estuary. See also least lettuce (Lactuca saligna, p. 72).

Small hare's-ear

Bupleurum baldense

Small hare's-ear is a member of the carrot and parsnip family, but differs from most members of that family in having simple, rather than deeply divided, leaves. Because of that, and its tiny yellow flowers surrounded by yellow–green bracts, it can look rather like the dwarf spurge, Euphorbia exigua. It can grow up to 25 cm (10 in) tall but is typically only a few centimetres tall, and flowers from May to July; fruiting finishes by September.

Several other species in the same genus occur sporadically in Britain, but among them only the slender hare's-ear, Bupleurum tenuissimum, is native here. It differs from the small hare's-ear in having narrower bracts that cannot conceal the flowers, and warty fruits.

Small hare's-ear was first found in Britain around 1801 by the Rev. Aaron Neck near Torquay, where it has since died out. It now grows in coastal grassland grazed by rabbits at two sites in southern England. One, containing up to a few hundred plants, is at Beachy Head in Sussex; the other is over 150 miles to the west near Brixham in Devon, and may boast 2,000 individuals in a good year. These are the species' northernmost outposts: on the continent it occurs across Italy, Spain, France and the Channel Islands. Small hare's-ear generally grows over calcareous rocks, and on the continent it is not limited to coastal locations.

The greatest threat to the small hare's-ear in Devon may be from people trampling the plants underfoot. In Sussex, the crumbling cliffs recede by 25 cm (10 in) a year and remove a large part of the population of small hare's-ears in the process, leaving only seeds that were fortuitously blown a short distance inland to produce the next year's plants.


The eastern end of the South Downs houses the only British localities of the spiked rampion, Phyteuma spicatum.

Club sedge

Carex buxbaumii

Club sedge is one of the more than 70 species of sedge (genus Carex) growing in the British Isles. Sedges are a difficult and much overlooked group, and the various species can be difficult to tell apart, even for experienced botanists. At first glance, club sedge resembles the common sedge, Carex nigra, but its flowering spikes are structured quite differently: they are all of similar appearance, with male flowers at the base of each spike, and female flowers thereafter. (Common sedge has one or two purely male spikes above up to four purely female spikes, sometimes with one transitional spike that is female towards the base and male towards the tip.) Its stems are 30–70 cm (1.0–2.5 ft) tall, with flower-spikes 7–15 mm (0.3–0.6 in) long.

Club sedge grows around the edges of lakes in areas that are under water at some points during the year. It is found across eastern Europe and Scandinavia, and in parts of Asia, as well as across much of North America. It was present on an island in Lough Neagh, Northern Ireland, until it died out in 1886 due to drainage and grazing. In Britain, club sedge is restricted to four sites in Scotland. The first location was discovered in 1895 near Arisaig, and a larger population was later found at Balnagrantach near Inverness. More recently, populations were discovered in Argyll in 1986, and at a second site near Arisaig in 1989. Each of these four populations varies in number from a few hundred to about 1,500, or up to 4,000 in the case of the largest population.

Little research has been carried out into Carex buxbaumii in Britain, so the reasons for its scarcity are not well understood. It is reported to be thriving in the sites where it occurs, and its patchy distribution suggests that other populations could yet come to light.

Starved wood-sedge

Carex depauperata

Starved wood-sedge is a rare and relatively unassuming sedge of deciduous woodlands. It occurs from Ireland south to Spain and across Europe to the Middle East, but appears to be very patchily distributed throughout that area; it is extinct throughout Germany, for instance. In Britain, it has been recorded at around a dozen sites, but only survives at two; a single site is known in County Cork, Ireland.

Starved wood-sedge forms large evergreen tussocks that produce flowering stems up to a metre tall. In this respect, it resembles the very common wood sedge, Carex sylvatica, except that its female flower-spikes only produce up to six rather large fruits each. Its leaf-sheaths are flushed red, somewhat like those of the spiked sedge, Carex spicata.

Starved wood-sedge was included in Plantlife's Back from the Brink campaign, and at one point it was indeed on the brink of extinction in Britain. By the 1950s, it was reduced to two sites in southern England. At one of these (near Axbridge, Somerset) there was just a single plant, and at the other (near Godalming, Surrey) the species had been lost by the early 1970s. At the Somerset site, one man, R. S. Cropper, took it upon himself to monitor and restock the last remaining population, and seemed to have single-handedly kept the species alive in Britain for some time. Meanwhile, after an absence of 15 years, starved wood-sedge made a reappearance in Surrey, after the 'Great Storm' of 1987 felled a large branch from a lime tree at the site where the plant had last been seen. It appears that the disturbance allowed the species to germinate from the seed bank. To supplement that natural population, plants have also been introduced to woodland in the grounds of Charterhouse School, just across the River Wey.


Excerpted from "A Guide to Britain's Rarest Plants"
by .
Copyright © 2017 Chris Dixon.
Excerpted by permission of Pelagic Publishing.
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Table of Contents

Introduction, 1,
Species (ordered alphabetically by scientific name),
Creeping marshwort, 6,
Alpine rock-cress, 8,
Bristol rock-cress, 10,
Norwegian mugwort, 12,
Pedunculate sea-purslane, 14,
Small hare's-ear, 16,
Club sedge, 18,
Starved wood-sedge, 20,
Large yellow sedge, 22,
Bristle sedge, 24,
Perennial centaury, 26,
Slender centaury, 28,
Red helleborine, 30,
Wood calamint, 32,
Lundy cabbage, 34,
Strapwort, 36,
Pigmyweed, 38,
Leafless hawk's-beard, 40,
Lady's-slipper orchid, 42,
Starfruit, 44,
Cheddar pink, 46,
Diapensia, 48,
Yellow whitlow-grass, 50,
Ghost orchid, 52,
Irish spurge, 54,
Radnor lily, 56,
Snowdon lily, 58,
Alpine gentian, 60,
Fringed gentian, 62,
Fringed rupturewort, 64,
Esthwaite waterweed, 66,
Land quillwort, 68,
Pygmy rush, 70,
Least lettuce, 72,
Teesdale sandwort, 74,
Holly-leaved naiad, 76,
Least adder's-tongue, 78,
Military orchid, 80,
Monkey orchid, 82,
Bedstraw broomrape, 84,
Oxtongue broomrape, 86,
Yellow oxytropis, 88,
Childing pink, 90,
Blue heath, 92,
American pondweed, 94,
Suffolk lungwort, 96,
Adder's-tongue spearwort, 98,
Sand crocus, 100,
Scottish dock, 102,
Drooping saxifrage, 104,
Triangular club-rush, 106,
Brown bog-rush, 108,
Round-headed club-rush, 110,
Perennial knawel, 112,
Viper's-grass, 114,
Cambridge milk-parsley, 116,
Fen ragwort, 118,
Moon carrot, 120,
Alpine catchfly, 122,
Downy woundwort, 124,
Water germander, 126,
Twin-headed clover, 128,
Upright clover, 130,
Spring speedwell, 132,
Dwarf pansy, 134,
Fen violet, 136,
Critical groups, 138,
Image sources, 143,
Index, 145,

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