Orobanche alba Stephan ex. Willd. (= O. rubra Sm.) (Thyme Broomrape)
Orobanche caryophyllacea Sm. (Clove-scented Broomrape)
Its British distribution is something of a mystery, since it implies a plant that requires warm and dry conditions, just gaining a foothold in Britain at a climatic limit. However, it occurs widely in Europe, including the Alps and Scandinavia. Perhaps it was a late arrival across the postglacial land bridge between Kent and France, before the English Channel formed, and since it appears to be obligately outbreeding, this may have limited its further chances of spread. An alternative theory is that it has arrived by wind-blown seed from France. Today it seems secure at least in its main site, though even there, a high grade piece of ground in private hands currently (2002) seems likely to be lost. Its conservation status is summarised by M. Jones (in Wigginton, 1999); it is listed as VULNERABLE and it is a scheduled protected plant under the Wildlife and Countryside Act, 1981.
As indicated by the name, the flowers have a distinctive scent of cloves.
Orobanche elatior Sutton (Tall Broomrape)
It is only locally frequent within its range and shows some evidence of decline, but it remains as our only species other than O. minor that is not rated as nationally scarce or nationally rare.
Orobanche rapum-genistae Thuill. (Greater Broomrape)
In the past, regarded as locally frequent throughout England and Wales, though scarcely reaching Scotland. However, over the past century, it has shown a dramatic decline, vanishing even where habitats seemed to remain suitable, and it appeared it might even be heading for extinction. Even so, it has held on in scattered sites, especially near the coast and in the south-west, and perhaps it is even showing signs of recovery. Its changes of distribution and recent status are described by Foley, in Stewart et al. (1994).
It has to be said that the location where it was photographed was remarkably unremarkable, and it must surely be overlooked elsewhere within uninviting gorse thickets!
Orobanche hederae Duby (Ivy Broomrape)
However, this rather neat native distribution is somewhat belied by the occasional occurrence of this species as an accidental or deliberate introduction on cultivated ivies, notably Hedera colchica, and on other cultivated members of the ivy family (Araliaceae) in inland gardens. In Europe it occurs widely, though sparsely, across much of southern and south-western Europe, evidently on the widespread ivy subspecies, H. helix subsp. helix, that it largely ignores in Britain. Possibly there is some ecotypic variation within the species?
O. hederae is rated a 'nationally scarce' species though not currently considered to be at any risk (Rumsey, in Stewart et al., 1994).
Orobanche picridis F.W. Schultz ex Koch (Oxtongue Broomrape)
In Europe it also (but rarely) parasitises Carrot (Daucus carota). It is widespread, but very rare and scattered, across the whole of southern Europe.
It appears to require dry, sunny slopes on lime-rich soils and the extant sites are on unstable, chalk seacliffs, where population sizes fluctuate from one year to another. Its conservation status is summarised by M.J.Y. Foley (in Wigginton, 1999); it is listed as ENDANGERED and it is a scheduled protected plant under the Wildlife and Countryside Act, 1981.
Nomenclatural note: Recent British authorities have considered this species to be the same as O. artemisiae-campestris (= O. loricata), a very rare and local parasite of Field Mugwort (Artemisia campestris) in southern and central Europe. Kreutz (1995) maintains them as separate species and that view is followed here (though they might be better considered as subspecies).
Other British speciesAs yet I have no photographs of O. purpurea, the Yarrow Broomrape, a very scarce and scattered species in southern England and Wales, or of O. reticulata, the Thistle Broomrape, which occurs, as its subsp. pallidiflora, on the Magnesian Limestone of South Yorkshire. Established introductions in Britain include O. crenata in South Essex (see page 1) and O. lucorum, the Barberry Broomrape, deliberately introduced in St. Andrews, Fife (Ballantyne, 2010).