Map of the Month - September 2023

September 2023’s Map of the Month is of Thistle Broomrape (Orobanche Reticulata)!

A map showing records for each 5km grid square containing Thistle Broomrape overlaid on a backdrop of the UK. The map shows records of Thistle Broomrape mapped as 5km grid squares for formal records between 1972 - 2023, as well as the area of Magnesian Limestone character (red). An outline of Yorkshire is shown in black.

NEYEDC assisted in a recent survey of Thistle Broomrape alongside Kay McDowell (local ecological consultant), to survey sections of land along the River Ure and River Wharfe for the Environment Agency. A root parasite of Carduus and Cirsium species, Thistle Broomrape can be found in scrub and grassland overlying Magnesium Limestone, and is considered a riparian species with most populations found within close proximity to the river. Also known as Yorkshire Broomrape, this plant has a highly selective distribution and within the UK can only be found in Yorkshire. Thistle Broomrape is a Schedule 8 protected plant, it’s rarity and complicated lifecycle result in large annual fluctuations in abundance. Unfortunately the year of 2023 appeared to be a year of temporary decline for Thistle Broomrape, with only one plant found within our survey area and many local landowners reporting an unusual absence of the plant this season. The plant requires specific sustained warm temperatures in the previous autumn to germinate, so lower than average temperatures last autumn may be responsible for the observed decline.

You can find out more about the Thistle Broomrape here: Orobanche-reticulata.pdf (bsbi.org). The last complete survey of the plant across Yorkshire remains M. J. Foley’s survey in 1992 which you can read more about in his paper here Wats19p247.pdf (bsbi.org.uk).