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.

ALSO IN THE AREA

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.

ALSO IN THE AREA

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...