A summer- or occasionally winter-annual found in open, sunny sites that are droughted in summer and relatively frost-free in winter. It grows with other therophytes on steep S.-facing banks, on compacted shingle or sand, in bulb-fields and gardens and at the base of roadside walls. Lowland.
P. tetraphyllum has been known in Dorset since 1770 and S. Devon since 1778. Populations can fluctuate dramatically in numbers, and it has been rediscovered at some sites after an apparent absence of many years. Comparison with the 1962 Atlas shows little change at the 10-km scale.
Count of 10km squares in Great Britain: 16
Count of 10km squares in Ireland: 0
Count of 10km squares in the Channel Isles: 14
Atlas Change Index: -0.04
RDB Species Accounts
Polycarpon tetraphyllum (L.) L. (Caryophyllaceae)
Four-leaved allseed, Gorhadog
Status in Britain: LOWER RISK - Near Threatened nationally, but VULNERABLE in mainland Britain.
Status in Europe: Not threatened.
P. tetraphyllum occurs in both semi-natural and artificial habitats, the former including steep therophyte-rich south-facing banks with high levels of insolation on the Lizard peninsula, West Cornwall, and in South Devon, and compacted shingle on Chesil Beach, Dorset. Man-made habitats include bulb-fields, gardens, and the base of roadside walls. In all its situations it favours open conditions with low levels of competition, subject to summer droughting and with a low incidence of frost. Its associates include a high proportion of annuals and biennials such as Anagallis arvensis, Aphanes inexpectata, Arenaria serpyllifolia, Bromus hordeaceus, Cerastium glomeratum, Erodium moschatum, Trifolium ornithopodioides, T. scabrum, T. subterraneum and Verbascum virgatum.
In Britain, this plant is normally a summer annual. Flowering can extend from April until as late as November or December and, unlike many annuals, it is apparently highly tolerant of drought. However, it may also behave as a winter annual, germinating in late summer or early autumn, the germination time varying according to the prevailing weather conditions.
In mainland Britain, P. tetraphyllum is very rare, and is currently known from only about six regular sites, in West and East Cornwall, South Devon and Dorset. Notwithstanding its habit of reappearing after long absences, this species does seem to have undergone a severe decline. Even in the 1920s it was becoming very scarce on the south coast. Many of its extant localities are long-standing ones (for instance, its Chesil Beach locality dates from 1774, whilst on the Lizard it was first found in 1872), yet populations are often very limited in extent, numbering only a few hundred plants annually, and have never spread. This scarcity on the mainland contrasts markedly with its status in the Isles of Scilly, where the plant is generally widespread in ruderal habitats and in bulb fields. The plant was not discovered in the Isles of Scilly until 1928, despite relatively high levels of botanical survey, and during the period 1928-1940 the plant expanded its range markedly (Lousley 1971).
In the Isles of Scilly, P. tetraphyllum seems reasonably secure, and only on the mainland can the plant be regarded as seriously threatened. A number of populations have been lost to urban expansion, and because of excessive overgrowth by coarse grasses and scrub brought about by the cessation of grazing and lack of disturbance.
As a native species, P. tetraphyllum is found in southern and western Europe and the Middle East, northwards to Britain and the Channel Islands, and eastwards to Turkey, Georgia, Syria, northern Iran, Arabia, and the Sinai peninsula. It is abundant around the Mediterranean. Elsewhere, it is a widely naturalised weed species, occurring in Asia, Africa, Australia, and South America (Davis 1967; Chater & Akeroyd 1993).
A. J. Byfield
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.