A bulbous perennial herb found as a possible native at only two localities: on dry, rocky S.- and W.-facing slopes in the Avon Gorge (W. Gloucs.), and on rough, sandy ground by the sea at St. Aubin`s Bay, Jersey. Both populations are very small. Lowland.
or alien. A. sphaerocephalon was first cultivated in Britain in 1759, and was first recorded in the wild in Jersey in 1836 and in the Avon Gorge in 1847, where it is normally thought to be native but may be alien (Lovatt, 1982). Recreational pressure and safety works within the Avon Gorge may have contributed to a gradual decline in recent years. It appears to be stable in Jersey. As it is now widely grown in gardens, it can be expected to spread as an escape.
European Southern-temperate element.
Count of 10km squares in Great Britain: 1
Count of 10km squares in Ireland: 0
Count of 10km squares in the Channel Isles: 2
RDB Species Accounts
Allium sphaerocephalon L. (Liliaceae)
Round-headed leek, Cenhinan Bengrwn
Status in Britain: ENDANGERED. WCA Schedule 8.
Status in Europe: Not threatened.
A. sphaerocephalon occurs on the wooded Carboniferous limestone cliffs of the Avon Gorge. It grows on shallow soil on ledges and slopes, most of which face south to west, are open to direct sunlight, and consequently can become very hot in the summer (Lovatt 1982). It grows in a community where the plant cover is incomplete because of the exposure of bedrock or the presence of rock fragments in the soil. Associated species include Bromopsis erecta, Crataegus monogyna, Dactylis glomerata, Festuca ovina, Geranium sanguineum, Hedera helix, Leucanthemum vulgare, Scabiosa columbaria, Sedum album, and sometimes the other onions A. roseum, A. vineale and A. carinatum, the last locally becoming a troublesome competitor.
It is a perennial, reproducing vegetatively and by seed. Flowers appear in June to August, and are pollinated by insects. The flowers are normally protandrous, and the plants are normally out-breeders, but can be self-pollinated. Vegetative propagation is by offsets (bulblets) and by bulbils.
The earliest record of this species in Britain was made in 1847, when H. O. Stevens discovered it in the Avon Gorge near Bristol, and this remains its only mainland site. The first record in the British Isles, however, pre-dates the Avon one, the species having been recorded in Jersey in 1833, where it still just survives on sandy ground in St Aubyn's Bay. In the Avon Gorge, populations have apparently always been relatively small and localised, and the plant is now restricted mainly to two small areas about 1.5 km apart. Flowering is variable from year to year, ranging from a few hundred to several thousand flowering heads. There is some indication of a general population decline, and in 1989 only 79 plants flowered after an exceptionally dry autumn and wet spring. Plants in the two main populations show slight morphological differences, and may be of different genetic stock. Both colonies lie within the Avon Gorge SSSI.
The Avon Gorge is heavily used for recreation and this undoubtedly has a major impact, particularly on the smaller of the two populations. In the past, large quantities of flowers were collected here, as mentioned by several early authors (e.g. White 1912). Picking still continues, despite legal protection, though to a much lesser extent. Works, aimed at reducing the risk from rock-falls to traffic on the road below, have in the past damaged the main colony (Taylor 1990f), but it seems to have recovered reasonably well. A threat is posed by encroaching scrub, particularly the alien species Quercus ilex and Cotoneaster spp., and regular cutting back is required. Some control of the alien A. carinatum, whose distribution overlaps that of A. sphaerocephalon, has been effected by the selective removal of whole plants (Frost, et al. 1991). A severe threat to A. sphaerocephalon has recently arisen from the cleaning, in 1995, of the Clifton Suspension Bridge by shot-blasting with copper slag containing high levels of other heavy metals toxic to plants. Spent slag, which fell into the Avon Gorge below, formed in heavy deposits on ledges and slopes, and it was estimated that 80% of the A. sphaerocephalon population may be affected (Rich, et al. 1996). Some clean-up works have been carried out.
In mainland Europe it is widespread and has a sub-Mediterranean distribution pattern, though it extends north to Belgium, and eastwards to Poland, south-central Russia, Turkey and Israel. In the Mediterranean region, it is typical of garrigue on rocky limestone and igneous mountainsides, but also occurs in vineyards, on waste ground and roadsides.
A. sphaerocephalon is generally regarded as a native species, though its status has been questioned, and the possibility of an ancient introduction cannot be entirely dismissed. Lovatt (1982) discusses its status in some detail.
M. J. Wigginton
PLANTATT - Attributes of British and Irish plants. (.zip 1455KB) This dataset was compiled and published in 2004, and last updated in November 2008. Download includes an Excel spreadsheet of the attributes, and a PDF explaining the background and nomenclature. Note that the PDF version is the booklet as published, whereas the Excel spreadsheet incorporates subsequent corrections. A hardcopy can be purchased from the Centre for Ecology and Hydrology.