Our Urban Flora team aims to visit all the towns in Scotland. On 5th May we were in Ardrossan (Ayrshire) getting quite wet. We spent the morning at the castle ruins, then we crossed the nearby rocky outcrops and descended to the harbour area, with a welcome coffee break in the Asda Supermarket. Both the rocks and the harbour were species-rich and we obtained many new records (the bryologists were especially excited). By afternoon the rained had ceased and we headed to a derelict site known as the North Shore. We picked our way across a landscape of rough blocks of reinforced concrete. We wondered, had this been part of a war-time military defence, guarding the Firth of Clyde? Perhaps. According to Secret Scotland (undated) it was once an oil depot, storing high-octane aviation fuel for the RAF in World War II. Locals call it ‘the old Shell site’. Secret Scotland states “The Defence of Britain Project gives the location of an anti-aircraft battery close to the depot but there is no other record currently known from RCAHMS, or Royal Artillery records, to support this, and no evidence visible on the ground. This is therefore assumed to be a mobile or light anti-aircraft battery, with carriage mounted guns, rather than a fixed or heavy anti-aircraft battery”. There is speculation that the oil tanks are still there, underground.
I found a good place to rest, a high perch to survey the scene and to eat my peanut butter sandwiches. The others pressed on, heads down, gazing at the vegetation. Suddenly came the cry “Broomrape ! Broomrape !” Sure enough we had found Orobanche, just coming into flower.
Orobanche minor as we first saw it, an emerging shoot. Photo: Chris Jeffree
It’s a totally parasitic plant, with no chlorophyll. It sucks sugars, minerals and water from its host via an underground connection. It is related to the toothwort, Lathraea clandestina which we wrote about in March 2021; both belong to the family Orobanchaceae.
Extending our search of this unusual site we found many individuals, always near clover Trifolium pratense (or in one case, possibly Trifolium hybridum) which we think is the main host. Orobanche minor is a rare plant in Scotland, but we were not the first to find it at Ardrossan. Its BSBI records begin in 1987, then in 2010, 2012, 2014 and it was last recorded in 2018. There are only eight scattered locations in Scotland where it has been recorded in recent times.
Further searching revealed mature individuals. Photo: Chris Jeffree
The Broomrapes in Britain have attracted much attention. An early account found 14 species of Orobanche (Rumsey and Jury 1991). This publication has very useful line drawings and distribution maps. Most of the species are quite local, and distinctly southern, and some have recognised subspecies. The discovery of a new subspecies of one of them was recently hailed as ‘a new vampire plant’ by Oxford University’s press department. You can see the reference to this below, but you might prefer to read the scientific account (Thorogood and Rumsey 2020) or the colourful blog from the BSBI: http://bsbipublicity.blogspot.com/2021/04/.
A mature individual photographed at the same site by Peter Mackie
‘Our’ species appears to be Orobanche minor var. minor but I want to make another visit to the site to be sure.
Orobanche minor seems to have a requirement for a very high pH (its Ellenberg number for the factor Reaction is 8), helping to explain its association with broken-up concrete. I wonder if the thermal character of the site, with subterranean concrete and possibly old oil tanks, provides the higher average temperatures that it may require.
Each species of Orobanche tends to have its own host. There are British species which are more or less specific to Yarrow, Bedstraw, Knapweed, Thyme, Thistle, Beans, and Ivy. In other parts of Europe, America and in Australia, Broomrapes are often serious pests of commercially important crops. The European sunflower crop is severely attacked by Orobanche cumana. The phenomenon of host specificity raises interesting questions about evolution, genetics and biochemistry. Much research has focused on these issues; when I searched for Orobanche on the Web of Science, some 1,700 papers in peer-reviewed journals were revealed covering all aspects although I have so far not found any work on the anatomy of the actual connection of parasite to host. Maybe I need to look at the older, German, work.
Why is the plant called Broomrape? Gerard’s Herbal (of 1597) shows a Broomrape clearly attached to a broom plant. I presume (and hope) that Gerard drew this from a specimen that he had carefully unearthed. However, modern articles do not describe this association with broom. Could it be that Orobanche minor was formerly found on broom but has evolved over a period of a few hundred years to attack other members of the Fabaceae?
We found 42 species of vascular plant on this derelict site. But soon it may be built on. Perusing the papers of the North Ayrshire Council I found the statement “Ardrossan North Shore is a key regeneration opportunity within North Ayrshire and is identified as a Strategic Development Area by the Adopted Local Development Plan”. It seems the plan is about to go ahead. In March 2022, a local newspaper, the Ardrossan Herald said “The North Shore regeneration plans include the creation of a new Ardrossan Academy and Winton Primary School community campus – incorporating an early years facility, leisure pool and library – plus sports pitches, a coastal path and up to 150 houses”. Local opposition focuses on health hazards, especially asbestos.
So we may soon be left with only seven locations of this interesting species.
Distribution of O. minor in the British Isles. Note the three recent records (green) in the East of Scotland. Map from the BSBI.
References
Oxford University (undated) https://www.ox.ac.uk/news/science-blog/botanists-unearth-new-vampire-plant-uk-carpark.
Rumsey FJ and Jury SL (1991) An account of Orobanche L. in Britain and Ireland”. Watsonia. 18: 257–295.
Secret Scotland (undated) https://www.secretscotland.org.uk/index.php/Secrets/MontfodeFuelDepot
Thorogood CJ and Rumsey F (2020) An account of Common Broomrape Orobanche minor (Orobanchaceae) in the British Isles. British & Irish Botany 2(3): 223-239.
©John Grace
Botany in Scotland 