In July 2023 four of us visited the Norfolk Brecks to look for insects and plants. We found several Breckland specialities but the best plant we found was Basil Thyme, Clinopodium acinos, which was growing in gravel at the side of a forestry track. It was a new species for me.

Basil Thyme

Basil Thyme, Clinopodium acinos. Norfolk Brecks, 30th July 2023.

Basil Thyme, Clinopodium acinos, is a member of the Mint family, Lamiaceae (note 1). It’s a pretty annual or short-lived perennial plant with stems to 25cm (10 inches) tall, though often much less. Its leaves are oval-elliptical and scented (note 2). It has whorls of flowers from May to September, which are normally violet with a white horseshoe-shaped mark at the centre.

Close up: Basil Thyme, Clinopodium acinos. Norfolk Brecks, 30th July 2023.

Basil Thyme grows on disturbed soils with not too much competition, where it can spread by seed.

Basil Thyme is a native plant in Britain and the Channel Islands. It’s usually found on calcareous soils, in dry grassland, on rocky ground and in arable fields. It also occurs as a casual on waste ground, in quarries and pits, on banks and beside roads and railways. In East Anglia Mike Crewe describes it as frequent on chalky soils in Breckland but scarce and declining elsewhere. The BSBI Species Account for Basil Thyme recommends that management of its habitat should aim for a short sward by the end of the growing season. Depending on the habitat, this can be achieved by grazing with sheep, cutting and removing the arisings, grazing by feral rabbits, or sometimes a mixture of all three.

Basil Thyme has declined substantially since the 1960s as more efficient methods of weed control on arable land have taken their toll. There is only one recent record from Scotland, from a golf course near Elgin in Moray (but see note 3). In Surrey, the plant has been recorded at Banstead Downs. In Leicestershire and Rutland the plant is now restricted to sparsely vegetated limestone quarries. In Wales, one of the places Basil Thyme grows is on the Great Orme, as pictured on the UK Wildflowers website (note 3).

In Ireland Basil Thyme is a neophyte which grows in sandy and gravelly places and some of these have been damaged or destroyed by gravel extraction.

Outside the British Isles, Clinopodium acinos is native in most European countries (but not Portugal) and its range continues east into Turkey, Iran and western Siberia. It is extinct in Morocco but introduced into Kazakhstan, parts of eastern Siberia, New Zealand’s South Island and parts of the United States (note 4).

If you can find a supplier, Basil Thyme makes a good garden plant but it doesn’t like competition from other plants and hates shade. It needs well drained, alkaline soil in full sun. It is very hardy and tolerates temperatures down to at least -15°C. Plants are short-lived but should self seed. The Useful Temperate Plants website says it makes a good, temporary ground cover. If you grow it, you could try using it as a herb for flavouring food. The Useful Temperate Plants website also lists some medicinal uses. The Celtic Wildflowers website lists pot grown plants, but these were out of stock at the time of writing.

Basil Thyme seed can be sown in early spring in a cold frame. Seedlings should be pricked out and potted up individually once they are large enough to handle and then planted out during the summer. Seed can also be sown direct in April or May. Existing plants can be divided by basal cuttings in late spring.

Also Available In White

Although my first photos in this blog post are of Basil Thyme with typical violet flowers, the first plants we found had white flowers.

Basil Thyme, Clinopodium acinos, with white flowers. Norfolk Brecks, 30th July 2023.

Basil Thyme Case-Bearer

Basil Thyme is the food plant of a rare moth, the Basil Thyme Case-bearer, Coleophora tricolor. The moth lays her eggs in August on Basil Thyme flowers and the larva spins a silk case over a single calyx of Basil Thyme and feeds within its protection. It overwinters on nearby grasses then makes a new case from hollowed out grass leaf-blades in late spring. Here it pupates and adult moths emerge in July and August.

The moth was first recorded in Norfolk in 1899 but after 1914 there were no records for over fifty years. The Norfolk Moths and Suffolk Moths websites show the current distribution in Norfolk and Suffolk, but understandably they keep exact locations of records confidential. There are photos of the moth on the Norfolk Moths website and in the Butterfly Conservation factsheet for the species. Norfolk and Suffolk are the only locations for the moth in the British Isles but it has been recorded in France and Greece. The moth can be attracted to light and flies on sunny days but the easiest way to find it is to search for the larval cases in autumn.

Two Other Finds

We didn’t find the moths but it was still a good day for insects. Highlights included our first Median Wasps (Dolichovespula media) and the striking tachinid fly, Ectophasia crassipennis. Both species are moving their ranges north as the climate warms.

The first British Median Wasps were recorded in 1980 in East Sussex and by 1995 the species had spread north as far as Cumbria and County Durham. The species has now reached Scotland. It is our second largest species of social wasp. (The Hornet, Vespa crabro, is the largest.)

Median Wasp, Dolichovespula media, on Snowberry flowers. Norfolk Brecks, 30th July 2023.

Ectophasia crassipennis is common in the Channel Islands. In 2019 it was recorded from several sites on the south and east coast of England. 2023 was the first year with records from the Norfolk Brecks.

A male Ectophasia crassipennis on a Wild Carrot (Daucus carota) flower. Norfolk Brecks, 30th July 2023. We had seen a female of the same species nearby four days earlier.

Notes

Note 1 – The BSBI uses the name Clinopodium acinos, as does Clive Stace in his New Flora (“New Flora of the British Isles“ by Clive Stace, Fourth Edition, 2019). Prior to a revision of the Lamiaceae in 2004 the plant was known as Acinos arvensis. The older name for the Lamiaceae, which I learnt as a child and used at university in the early 1980s, was the Labiatae.

Note 2 – The BSBI species account says the leaves are “faintly aromatic“, while Mike Crew says they are “strongly aromatic“. (The pungency will depend on the weather and perhaps growing conditions, as well as the observer’s sense of smell.)

Note 3 – https://plantnetwork.org/wordpress/wp-content/uploads/4714/clinacin.pdf lists the number of native sites for Basil Thyme in each county in Scotland, England and Wales. The document is undated. The only Scottish site listed is in East Lothian, rather than Moray. Overall, Norfolk leads with 28 sites, with Wiltshire next with 16 sites. There are seven sites listed for Suffolk, where Basil Thyme is a Suffolk Biodiversity Information Service priority species.

Note 4 – For the United States, Plants of the World Online lists New York, Vermont and Wisconsin but the Native Plant Trust lists Connecticut, Maine, Massachusetts and Vermont in New England. A BONAP (Biota of North America Program) map on the Native Plant Trust website shows a wider distribution for Clinopodium acinos in the United States.