Notes on Essex Specialities. 8: the fifty year history of Orobanche crenata in Essex
with one plant reaching 116cm!- thus beating our height record. A record from Clehonger, Hereford
of O. rapum-genistae on Vicia faba is also pretty unlikely, and probably constitutes another occurrence
of O. crenata. Other, probably more obvious human introductions are an occurrence on Pelargonium
at Cholsey, Bucks, in 1938 (C. Rea HbOXF); on a potted carrot at the Cambridge Botanic Garden
(date ???); thriving very well on a potted Pelargonium brought to the BSBI exhibition in 1984, and
a single plant in the Natural Order Legume beds at Kew on Vicia bithynica persisted in these beds for
several years up to at least 1999. It also occurred on a plot of Field Beans, Vicia faba in 1985 at one of
tire National Institute of Agricultural Botany's trial sites in Cambs. In that case it was found that the seed,
imported from Italy, was contaminated with Orobanche seed (Flood 1991). None of these occurrences
seem to have survived for any length of time, though of course the Gloucestershire plants may have
been related, the later sightings developing from dormant seed dispersed on the wind several years
previously.
In the same year as the author discovered the Cranham Marsh colony how ever, a Mr Kumar reported
the occurrence of several spikes in his garden, some 3km due north at 71 Peterborough Avenue, as
did his neighbour at 69. Patrick and Mary Smith also had a few spikes turn up in their garden in
Gaynes Park Road. The plot began to thicken when Fred Rumsey, who was studying our British
Broomrapes at Reading University, tracked down a pressed specimen in the Kew Herbarium, collected
by H.C. Denning, from a flower bed in another nearby Upminster garden (13 New Place Gardens)
just 2km NNW of Cranham Marsh, 'host unknown', way back in 1951, the plant having first appeared
in 1950.
Thus it is beginning to look as though O. crenata had become well and truly established in the
Cranham area, probably on a broad bean or pea crop initially, sometime prior to 1950, and had been
tiding itself over on wild Vicias, as well as no doubt remaining dormant in the crop fields. Prior to a
change of tenancy around 1980 the fields around Cranham Marsh had largely been used for market
garden produce (even the drains on the Marsh itself were originally used as watercress beds), the
soil in the area being a rich alluvial silt and classed as Grade 1 laird. Thus O. crenata could have
originally been introduced on one of these crops and put down a sufficient seed bank to keep popping
up whenever the right crop came along. After 1980 the surrounding fields were extensively drained
and put down to cereals, that is until 1997, when the three fields of newly planted peas triggered the
explosive spread of the broomrape.
It is not a particularly fussy parasite and can get by on a variety of potential hosts belonging to a
range of dicotyledon plant families. On the continent its a circum-Mediterranean species forming a
narrow band along the Mediterranean coasts of southern Europe from Portugal, through southern
Spain and France, most of Italy and Greece, and east through Turkey to the Caucasus, as well as
skirting in a narrow band along the north coast of Africa west to the Canary Islands. In these areas it
parasitizes a variety of native and crop legumes as well as cultivated carrots, and is mainly found in
arable fields and on roadsides. As a casual it occurs temporarily in central and northern Europe. In
Sweden it is well established in botanic gardens (Kraft 1979) and has been recorded parasitizing
Pelargonium zonale, Begonia tuberosa, Satureja hortensis, Tropaelium majus, Calendula arvensis
etc., in addition to the Legume genera Lathyrus, Vicia, Lens, Lupinus, Trifolium, Pisum and Cicer
(Chick Pea).
Why then is its native distribution so closely tied to the Mediterranean? Possibly its later flowering
further north results in most of the immature spikes being destroyed when the crops are harvested so
that it never manages to sustain its seed bank for more than few years. Or perhaps it needs a warm
soil to grow fast enough to keep up with its host. Certainly it seems to do best at Cranham in really
Essex Naturalist (New Series) 20 (2003)
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