Bupleurum falcatum

Bupleurum falcatum L. (Apiaceae)

Sickle-leaved hare's-ear

Status in Britain: CRITICALLY ENDANGERED.

Status in Europe: Not threatened.

In 1831, when first found at Norton Heath, Essex (Sowerby 1934), B. falcatum was well-established and in great abundance in hedges between fields to a considerable distance on both sides of the road. It remained abundant until at least 1883 (Crompton 1974-86), but road improvements and changes in land use destroyed most of the population by 1943 when only about 50 plants remained. Despite low numbers, the population survived for the next twenty years. In 1962, during hedge cutting and ditch clearance, a fire was lit on the site (Jermyn 1974), which seems to have quickly led to the plant's extinction there. In 1979, a small colony was discovered near to the last. However, bearing in mind the short-term viability of the seed, it seems unlikely that seed or plants had survived since 1962 without being reported. Therefore, these new plants almost certainly arose from seed deliberately sown in 1978. Ironically, shortly afterwards, scrub was burnt on the very spot and, as if to make certain of its demise, the verge was sprayed all the way from Epping to Ongar with herbicide in 1980.

The segment of road along which the plant formerly grew was finally bypassed in a road-straightening operation in 1985/6. A site between the old and new roads was landscaped out of the chalky boulder clay, and this was sown in 1988 (Birkinshaw 1990e) with large quantities of B. falcatum seed from plants in the author's garden and from the Cambridge Botanic Garden (derived from pre-1962 Norton Heath plants). Although still extant, the colony is small and vulnerable. There were 32 plants in 1991, but just 25 in 1994. In July 1995, 51 plants were present, but browsing by rabbits had reduced the number to 24 by early August. The latter plants survived because they were protected from grazing by abundant Cirsium arvense, C. vulgare and Picris echioides that surrounded them. Numerous small plants and seedlings occurred in uncountable clusters around the larger plants. By July 1996, however, the population had been reduced to three flowering plants and a small number of seedlings. Unless rabbit-proof fencing is installed around the boulder clay mounds, it is unlikely that B. falcatum will persist at Norton Heath. It has been reported in the British Isles, as a casual only, from a very few other places.

B. falcatum is a biennial or short-lived perennial with umbels of conspicuous bright-yellow flowers. It is quite widely grown in botanic and private gardens throughout the British Isles, where it will grow luxuriantly unless grazed by rabbits. Only some plants have the asymmetric leaves that give the plant its name. That feature seems likely to be caused by unequal growth of the two half-laminas, either side of the midrib, owing to damage inflicted at the bud stage by frog-hoppers, which often infest the plants. Seed is copiously produced, but is viable for only about a year. Seedlings are produced in large numbers around parent plants, but are unable to complete in a closed sward, being favoured by dry, bare, calcareous mineral-soils, with minimal humus.

Although recently found in Britain as a sub-fossil in deposits from the Flandrian interglacial (Field 1994), it is extremely unlikely that the Norton Heath population was a relict from a more widespread distribution in the Flandrian. Such a showy plant is unlikely to have appeared at Norton Heath much before 1831 without someone reporting it. Its persistence there must also have gone hand-in-hand with rigorous control of the local rabbit population, a practice only relaxed in the area following the myxomatosis epidemic.

On the continent B. falcatum frequents dry sunny locations on slopes and ridges, and the scrubby southern fringes of woods on calcareous clayey and sandy soils. It is widely distributed in southern, central and eastern Europe, extending northwards to Belgium, Germany, Poland and Central Russia. Although plentiful in north-west France, its distribution elsewhere in northern Europe is patchy.

K. J. Adams