STATUS, DISTRIBUTION
and IDENTIFICATION
Notes on Essex Specialities. 8: the fifty year history of Orobanche crenata
Forskal, the Carnation-scented (Bean) Broomrape in Essex
KEN ADAMS
School of Health and Biosciences, University of East London E15 4LZ
Abstract
This magnificent plant has been present in the area around Cranham, Upminster in south Essex for
at least 50 years, the only place in the British Isles that it seems to have become established. An
estimated half a million plants parasitized three fields of peas at Cranham in 1997 thus enabling it to
put down an enormous seed bank locally and to disseminate millions of its minute seeds via the
wind. With an estimated viability of 10-12 years this plant could become a major crop parasite on
peas and beans or carrots in south east England in future decades.
In late July 1975, while surveying the fen at Cranham Marsh, the author detected a strong rather
pungent carnation/clove-like scent on the damp evening air and tracked it down to the fallow margins
of an arabic field bordering a reed bed, too wet to grow a successful crop, that had become colonised
by a large colony of Smooth Tare Vicia tetrasperma. Scattered among the Vicia some 80 spikes of a
strange new broomrape were in full flower, and it was these that provided the powerful carnation
scent [sadly, most commercial carnation varieties these days have lost their scent]. Digging down
underneath a plant indicated a close association between the root systems of the broomrape and the
Vicia. Broomrapes have no chlorophyll of their own and are totally parasitic on the root systems of
other plants. The minute seeds, comparable to the dust-like seeds of orchids, are produced in vast
numbers of up to several hundred thousand per plant. They lie dormant in the soil until a chemical
signal exuded from the root system of a suitable host triggers their germination. Despite their minute
size, and therefore restricted food reserves, the seeds can retain theirviability for l()-15yrs. Though
most species take months or years to appear above ground, O. crenata can germinate along with its
host, flowering and setting seed before a crop of peas or beans (its main hosts) has been harvested.
Broomrapes can also persist for at least a year (and probably longer) underground after flowering.
The fresh flowers of O. crenata arc white with crinkly lobes and delicate lilac veins, and have a pale
sulphur yellow throat (inside) (see Plates 4a. 4b). They rapidly go over however, the white corolla
lobes soon turning a patchy brown. The bilobed stigmas are also initially white, but rapidly him
orange-brown. The markedly hairy stems are very7 sturdy and can reach 120cm, though the largest
we have recorded was 58cm. O. crenata is distinguished from all our oilier broomrapes by the 2 upper
lobes and 3 lower lobes of the corolla being bent outwards, and by the two lobes of the calyx, which are
free from each other at the base, and are each bifid almost to the base. The flowers are large, some 20-
30mm in length in well grown plants, and the scent is unmistakeable. Broomrapes produce nectar in
patches at the base of the stamens and are largely pollinated by bumblebees and other bees, the scent
Essex Naturalist (New Series) 20 (2003)
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