“The wonder of the world
The beauty and the power
The shapes of things,
Their colours, light and shades
These I saw,
Look ye also while life lasts.” (note 1).
Common Dodder, Cuscuta epithymum. Bryant’s Heath, Norfolk, mid July 2021. (The purple in the background is Bell Heather, Erica cinerea.)
My Favourite Vampire
For some people it’s Dracula, but my favourite vampire is Common Dodder, Cuscuta epithymum. It is always a pleasure to see it, with its stems twining like pink spaghetti or silly string over gorse and Heather.
Cuscuta epithymum is a member of the Convolvulaceae (Bindweed family) and twines its stems over vegetation like its leafy green relatives Field Bindweed (Convolvulus arvensis) and Hedge Bindweed (Calystegia sepium). But Dodder is a parasitic plant with much smaller flowers and small, scale-like leaves. It lacks chlorophyll and depends on its host plant for its supply of nutrients (note 2).
In Norfolk, Common Dodder grows on sandy, acid heaths, including Kelling Heath, Buxton Heath, Holt Lowes and Bryant’s Heath and parts of Beeston Common. Here, it sprawls low over the ground, but at Incleborough Hill, near West Runton, Dodder it grows to a massive size as it clambers over Common Gorse bushes.
In Norfolk Common Dodder’s hosts are gorse (Common Gorse, Ulex europaeus and Western Gorse Ulex galii) and Ling (Calluna vulgaris) and these are the commonest host plants, according to Stace (note 3). But Cuscuta epithymum will parasitise a wide range of plants, including Common Hawthorn and especially clovers (Trifolium sp.) and other members of the Pea family (Fabaceae) such as Dyer’s Greenweed (Genista tinctoria). It is sometimes called Clover Dodder or Alfalfa Dodder because of its host plants. In the British Isles Cuscuta epithymum sometimes parasitises Wild Thyme (Thymus polytrichus) and in southern Europe it grows on Conehead Thyme (Thymus capitatus), where it apparently takes on the pungent smell of is host. Its specific name, epithymum, comes from growing on thyme.
In the British Isles Common Dodder is most abundant in the south of England but occurs as far north as Fife in Scotland and in parts of Wales and Ireland. As well as heathland, it grows on chalk downland and fixed dune grasslands and sometimes as a casual on field crops and in arable field-borders at the northern and western limits of its range. Dodder has declined since the 1930s as its habitats have been lost, through ploughing of downland and increase in scrub and the destruction of lowland heaths through forestry and house building.
Common Dodder flowers
Common Dodder flowers from July to September in the British Isles, but much earlier in southern Europe. (The First Nature website has photographs of the plant flowering in early April in Crete.) The flowers can be pollinated by insects or self-pollinated. Dodder flowers sometimes smell of rotting fish (perhaps to attract Blowflies as pollinators). In contrast, the Plants For a Future website refers to the “remarkably sweet perfume” of the flowers, which is “especially pronounced towards evening“. I sniff the flowers whenever I remember to, but I’ve never noticed much scent (but see update July 2023).
Common Dodder is a native of Europe, West Asia and northern Africa but has also been introduced into North America, South America, Japan, Australia and New Zealand. It is also found in parts of eastern and southern Africa, either as a native or introduction. Across its range there are at least two subspecies and, within these, several varieties. These are distinguished by differences in their flower structure as well as the number of flowers and how they are grouped.
Common Dodder can grow as an annual or perennial plant.
It has small seeds (about 1 millimetre in diameter) and these can lie dormant for years. But seeds cannot live ever and if an area of heathland remains unmanaged for a long period of time Dodder may be unable to survive.
If the conditions are suitable Dodder seeds will germinate as the weather warms up in spring (from April onwards). When the seed germinates, a swollen, root-like organ emerges from the seed case and seeks out a suitable host (note 4). At this stage the plant is using nutrients stored in its seed and it must find a host plant quickly or it will die.
Once a host is found, Dodder attaches to it with a sucker and forms a haustorium (a structure that penetrates the host’s tissue and draws in nutrients; see my post on Mistletoe). The root-like organ withers and from this point onwards nutrients are taken from the host plant through the haustorium and the Dodder starts to grow very rapidly, twining anti-clockwise around its host (as does bindweed, note 5). It is vital that the plant stays attached to its host and the Dodder produces a kind of glue to ensure this happens.
Common Dodder can also grow as a perennial by forming an overwintering gall within a stem of its woody host. In autumn the twisting stems die back but the Dodder survives and produces new growth in the spring. This strategy removes the risk of not being able to find a host (note 6).
Gerald Durrell refers to Common Dodder in his book “The Amateur Naturalist” (note 7). It’s a moment of high drama: “In the heath communities of the south you can find the innocent-looking common dodder. This has no leaves but a hard red stem and clusters of delicately-shaped pink flowers. But don’t be misled by its appearance, for it is a sort of plant Dracula. It climbs up its victim anticlockwise and the roots from its wiry stem pierce the flesh of its host and suck out the nutrients. In some cases the dodder, like Dracula, leaves its victim dead, drained dry.”
Dodder can undoubtably affect the vigour of its host plant but killing the host is not in a parasite’s best interests and growth is usually dependant on the vigour of the host plant.
The Plants for a Future website gives a number of medicinal uses for Dodder, including problems with the liver and gall bladder, urinary complaints and gout. It warns that the plant should not be used by anyone suffering from haemorrhoids. During medieval times, Dodder was used as a cure for depression, but its consumption apparently causes thirst and dryness of the mouth.
My most recent sighting of Common Dodder was at Bryant’s Heath, near Felmingham in North Norfolk. Most of the Dodder was the usual pink colour, but some of the plants were yellow.
Common Dodder with yellow stems and flowers. (You can see some pink strands as well.)
The pink in wild type Common Dodder stems is due to the presence of anthocyanins (cyanidin glycosides) (note 8). The yellow plants must have a block in the anthocyanin biosynthetic pathway. Stace (note 3) mentions these occasional variants: “stems reddish except yellowish in rare albinos”.
A quite separate plant is Yellow Dodder, Cuscuta campestris. This is a North American plant that is sometimes accidentally introduced to fields (where Carrot is one of its hosts) or in bird food mixes. I saw it growing at Natural Surroundings in North Norfolk a few years ago and it persisted in a friend’s garden on the outskirts of Norwich for several years.
The third species of Cuscuta in the British Isles is Greater Dodder, Cuscuta europaea, which usually grows on Stinging Nettles (Urtica dioica), often near water. It is rare and I have yet to see it.
Mike Crewe’s Flora of East Anglia website has some good pictures of all three species on one page for easy comparison.
Notes
Note 1 – I love this quote. It originally comes from a Cumbrian gravestone. It was used by the naturalist, illustrator and author BB (Denys Watkins-Pitchford) in his preface to “Down the Bright Stream”, the second of his books about the last four gnomes in Britain (the first is “The Little Grey Men“). The gnomes are led by Dodder, the oldest and grumpiest gnome, and this provides my feeble excuse for including it here.
Note 2 – Other completely parasitic plants I’ve written about include Ivy Broomrape, Purple Broomrape and Purple Toothwort.
Note 3 – Clive Stace, “New Flora of the British Isles“, pages 603 – 604. (Fourth Edition, 2019.)
Note 4 – Common Dodder “sniffs out its hosts, by recognising their chemical signature”. https://www.nationaltrust.org.uk/west-runton-and-beeston-regis-heath/features/the-amazing-world-of-dodder-cuscuta-epithymum.
There are some good – and a bit creepy – videos of various species of dodder on You Tube, such as https://www.youtube.com/watch?v=5gPuXtmrP0E.
Note 5 – As mentioned in the Flanders and Swann song “Misalliance”, on their album “At The Drop of a Hat”, although the song is really a commentary on politics and class rather than Botany.
“The fragrant honeysuckle spirals clockwise to the sun,
And many other creepers do the same.
But some climb anti-clockwise, the bindweed does, for one,
Or Convolvulus, to give her proper name.” – Flanders & Swann.
You can listen to the song on You Tube at https://www.youtube.com/watch?v=WhJ1MDfvix4.
Note 6 – The information in the previous four paragraphs mainly comes from the Kew Gardens website, http://powo.science.kew.org/taxon/267419-1. The direct contact between species of Cuscuta and their hosts is one of the reasons why Cuscuta species are the most rapidly growing parasitic plants.
Note 7 – Gerald Durrell with Lee Durrell, “The Amateur Naturalist”, Dorling Kindersley (1982), page 72.
Note 8 – See page 121 in the 1941 paper by Beale, Price & Sturgess, “A survey of Anthocyanins VII. The natural selection of flower colour”, https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.1941.0008.
Update July 2023
On 20th July 2023 I visited Buxton Heath and had another sniff of Dodder. This time the flowers had a distinct not very pleasant scent that combined sweetness and decay.
There were no Blowflies but the flowers were attracting Bee-wolves (Philanthus triangulum). These large, impressive wasps are now common in southern England, having spread rapidly since the 1990s. We now have them visiting our garden (they love Echinops flowers) and they nest on road verges in Norwich. Females catch worker Honeybees to stock their nest holes and feed their larvae.
Bee-wolf (Philanthus triangulum) on Dodder flowers. Buxton Heath, 20th July 2023.
