Thymus serpyllum

Thymus serpyllum L. (Lamiaceae)

Breckland thyme

Status in Britain: LOWER RISK - Near Threatened.

Status in Europe: Not threatened.

T. serpyllum is confined in Britain to the Breckland, where it is more or less restricted to dry, sandy soils overlying chalky drift or on inland dunes (Pigott 1955). It grows in areas of short, open grassland, particularly on heaths grazed by rabbits or sheep, and frequently on bare patches between rabbit-grazed bushes of Calluna vulgaris. It is tolerant of acidic sands and is frequently seen in association with Filago minima, Ornithopus perpusillus, Teesdalia nudicaulis and Cladonia species, together with Festuca ovina, Galium verum, Koeleria macrantha and Pilosella officinarum. It is light-demanding and intolerant of competition. 

It is a slow-growing mat-forming perennial, extending by runners. Flowering is in July and August, later than T. polytrichus, which also has non-flowering runners, but at the same time as T. pulegioides, which lacks them. Reproduction is by vegetative spread and by seed. The rather woody runners root at the internodes, and in suitably open habitats may form extensive and profusely flowering tracts in late summer. Identification of this species can be difficult, as plants are often stunted by drought, nutrient-deficiency and grazing (Pigott 1954).

Sites for T. serpyllum were lost as heathland was ploughed for cultivation or forestry. Furthermore, the decline in rabbit and sheep-grazing also reduced the areas of short, open turf. Surveys undertaken in 1991 and 1993 (Leonard 1993) have shown that heaths and roadside verges in West Suffolk support fifteen stations for T. serpyllum. It occurs in three sites in West Norfolk, but no longer occurs in Cambridgeshire. At the present time, the closely mown turf surrounding the runways at RAF Lakenheath make this its most extensive known site. The recovery of the rabbit population and increase in sheep-grazing in Breckland should ensure the creation and maintenance of bare ground which it requires for germination and vigorous growth (Pigott 1955).

Unlike the British populations, T. serpyllum is variable in Europe, where several subspecies and varieties are recognised. The type subspecies ranges from England, north-east France and the Netherlands, eastwards to Germany, southern Scandinavia and north and central European Russia. Its habitats in Europe are similar to those of Breckland, sharing such species as Herniaria glabra, Silene conica and Veronica spicata.

Y. Leonard