Sometimes, in the middle of winter, the only escape is to look forward to long summer days full of plants.
In the middle of June last year we took the train to Sheringham on the North Norfolk coast and walked to Cromer. Descending Beeston Bump we were rewarded with a new species of plant, Purple Broomrape, Orobanche purpurea. This is a very handsome beast, with dark purple flowers on a purplish brown stem. It looked very striking against the greenery of other plants, including grasses, horsetails (Equisetum), Kidney Vetch (Anthyllis vulneraria) and Yarrow.
Mistletoe, which I wrote about in December, is a hemi-parasite: although it takes some of its nutrients from its host, it possesses chlorophyll and makes its own sugars. Broomrapes are holo-parasites: they are utterly dependent on their hosts for food.
Purple Broomrape has no leaves and does not photosynthesise. It has an underground tuber and attaches to its host underground by means of haustoria. It is a member of family Orobanchaceae, which contains about 90 genera and 2000 species of herbs and shrubs distributed throughout most of the world. All, except for the genera Lindenbergia and Rehmannia, are hemi- or holo-parasites on the roots of other plants. See Wildflowers-and-Weeds.com for some lovely photographs of American members of the family.
Fourteen species of Orobanche have been recorded in the British Isles. Although “A Flora of Norfolk” (Gillian Beckett, Alec Bull & Robin Stevenson, 1999) lists five species of Orobanche in Norfolk, Hemp Broomrape (O. ramosa) was only recorded in 1880 and Greater Broomrape (O. rapum-genistae) was last seen in the county in 1986. This leaves three species: Purple Broomrape, Common Broomrape (O. minor) and Tall or Knapweed Broomrape (O. elatior). I have seen the latter once, on Marriott’s Way near Norwich, though it is more common in West Norfolk. In contrast, Common Broomrape is much more widespread and is found with a variety of host plants, including clovers (Trifolium) and various members of the Asteraceae (daisy family). Several years ago it was abundant amongst shrubs by a car park in Westwick Street in Norwich and we found it growing amongst Hyssop in Grapes Hill Community Garden in 2012.
Purple Broomrape is much rarer than its common and widespread host plant, Yarrow. Nationally, Purple Broomrape is a plant of clifftop grasslands and, sometimes, disturbed places, on dry, slightly alkaline soils. It has the habit of disappearing for several years and then reappearing, which suggests that it can persist without flowering for many years, or has long-lived seeds. In the UK it is classed as vulnerable (see map and list of sites), but North Norfolk is one of its hotspots, along with the Isle of Wight and the Channel Islands. It can also be found on sand dunes in the Netherlands and its natural range is across Europe, as far south as Spain, Portugal and Greece, east to central Russia, the Caucasus, Asia Minor, Pakistan and India and north to Sweden. It has also been reported from Canary Islands, Morocco, and North America. (In Iran it has been recorded on a close relative of Yarrow, Achillea wilhelmsii.) However, it is endangered in much of its range as grasslands are destroyed and agriculture intensifies. The paper by Renata Piwowarczyk, “Orobanche purpurea (Orobanchaceae) in Poland: current distribution, taxonomy, plant communities, and preferred hosts” (Biodiv. Res. Conserv. 26: 73-81, 2012) gives a good, if sobering, summary.
At the time of writing, the Plants for a Future website lists ten species of Orobanche, but not O. purpurea and given its rarity it would be criminal (literally) to harvest it. Our Orobanche minor has no known edible uses, but Orobanche ammophyla is used as a food and medicine in China (mind you, so are tigers) and other edible and medicinal species include the North American Orobanche fasciculata.
If you want to see Purple Broomrape on Beeston Bump, you can follow Walk 8 in this walk leaflet. Stick to the paths and go in June or July. Last year there was lots of Purple Broomrape, but be aware that the number of flowers varies from year to year.