by Brian Ballinger
Brooomrapes in the genus Orobanche are in the Orobanchaceae family. Broomrapes are totally parasitic, lacking any chlorophyll. They have erect stems with sessile irregular zygomorphic flowers with a 2-lipped corolla. Unlike the closely related toothworts (Lathraea) they lack underground rhizomes.
Broomrapes are familiar to some of us from Southern Europe but are less frequent in Britain and generally scarce in Scotland. Four Scottish species are described, all locally scarce. The differentiation of the species is not always easy, although the presence of the host plant can often help.
Orobanche minor (Common Broomrape). In spite of its name this species is not at all common in Scotland. It is native but has sometimes been introduced accidentally.
It is a root parasite on a variety of plants in Fabaceae (pea) and Asteraceae (daisy) families. The flowering stems are red or sometimes yellowish and the flowers are purple veined. The stigma is usually purple.
O. minor is fairly widespread in England but scarce in Scotland. I first saw it in the Central Belt some years ago where it is recorded in West Lothian. My recent experience of this species has been much further north at Fearn, by Tain in a disused railway goods yard near my flat there. About 11 years ago I found some dead heads and examination of fresh flowers revealed a broomrape, later identified as Common Broomrape.
There are many Red Clover (Trifolium pratense) plants round it and this seems likely to be the host plant. In the following years it has thrived in spite of some interference by rail operations. It is difficult to know how it arrived here, but probably the railway was involved. This site is 100 miles north of any other known location of this species.
Ororbanche hederae (Ivy Broomrape). As its name suggests this species is parasitic on Ivy (Hedera) species. It is rather similar to O. minor but the stigma is usually yellow and the corolla tip is curved down and cream coloured.
Although more frequent in England the only Scottish location has been in Wigtownshire where I saw it some years ago and where it persists. However much to my surprise it appeared in Dundee this year in the grounds of a University building in the west of the city. During my pandemic exercise walks I had noted dead heads and later Broomrape flowering heads have appeared close by a dense patch of ivy. The identification was confirmed by Hamlyn Jones and Fred Rumsey. Again, this site is 100 miles north of any known locations but only 200 metres from my front door. How it got here is a mystery. It is occasionally planted but this site does not look likely for this.
Orobanche alba (Thyme Broomrape). This is the most widely recorded Scottish species growing on the north west coast and islands on base rich sites as well as the Fife coast where I have seen it. It is parasitic on Thyme (Thymus polytrichus). O. alba is purple red and relatively short. It can be vulnerable to grazing.
Orobanche rapum-genistae (Great Broomrape). This species is tall and is parasitic on gorse and broom. It has only been recorded in the Dumfries area in Scotland, but given my recent experience maybe it will appear somewhere else.
The contrasting distribution of the four species is seen on the BSBI distribution maps, shown below. Many questions remain about the reasons for these distribution patterns.
In botanical exploration one always needs to be prepared for the unexpected as unexpected things sometimes happen.