A-Z of botany: Parasite


P is for parasite.
Parasitic plants, that depend on other plants for their nutrients, are not big in gardens. Apart from some fairly natural aversion to the idea, to grow a parasite you have to first grow a host plant and then introduce the parasite – and garden centres don’t stock them. The best known is mistletoe but, as that is not a true parasite that can wait a few lines and I will deal with a proper parasite first.

The Orobanche family is the most important and true orobanches are rather lovely things with tall spires of rather orchid-like flowers in browns, white and purple (usually) and the most common and easy to accommodate is the handsome O. hederae that is native to the UK and not difficult to establish because the host (ivy) is common. Collect seeds and sprinkle them in a clump of ivy and there you go!

Also in the family are the toothworts (Lathraea), including the native L. squamaria (above). Most commonly a parasite of hazel, it will also grow on other tree roots and the common name comes from the way the flower stems look like a jaw bone set with teeth. It is not often seen because, like all true parasites, there are no leaves and the plant is only visible when the plant is in bloom (usually March to May). It can be difficult to photograph because, since the plant needs no light, the flowers can emerge in very gloomy places. More common in gardens is the exotic Lathraea clandestina which has crocus-like, purple flowers in spring in tight clusters. The largest flower in the world is produced by a parasite, Rafflesia arnoldii, from Indonesia which has blooms that can weigh 10kg and be 1m across and is only visible when the buds emerge – though the smell is more than capable of drawing attention to it.


Rather less exotic is mistletoe. In the UK we blithely go on about mistletoe but our native Viscum album, is just one of the many mistletoes (members of the Loranthaceae family) that are found across the world, all growing on, and in, the tissues of host plants. Our version is only a semi-parasite because it has pairs of green leaves on its branches that can manufacture food for the plant. The idea of parasites suggests that the mistletoe will kill the host but that is never in the interest of the parasite because then it will die, along with the host. But mistletoe will damage a host plant and as the plant gets bigger the load on the host increases as it needs more sap and it is possible for the end of the branch to decline and even die.


Mistletoe can grow on a wide range of plants and is most common on poplar, lime (above)  and apple though I have seen it on other Rosaceae such as chaenomeles and crataegus (below) and acer. The most ‘magical’ is from oaks but that is not common.


It is often, rightly, written that the seeds are spread by birds, but they do not always pass through the digestive system. Mistle thrushes and blackcaps treat them in different ways. The thrushes eat the berries and excrete the seeds in sticky strings while blackcaps wipe. They eat the sticky white flesh (Viscum album means, literally, ‘sticky white) and wipe the seeds off their beaks onto the bark of the branches. It is here, pushed into the crevices of the bark, that the seeds germinate and push their haustoria into the cambium (active tissue just below the bark) and, after a year or two, send out the first pair of leaves. The plants grow very slowly, producing just one pair of leaves and a stem each year to increase the length of each stem, though each does divide in two so the clump gets wider and wider. Mistletoe is dioecious, meaning that male and female flowers are produced on separate plants. If you have just one clump on a tree it may not have berries if it is a male or a lonely female. Of course, we all want berried twigs at Christmas.


Cutting pieces will not harm the plant and it will control growth so may be beneficial for the host plant. It is often stated that the seeds grow best if planted on the same tree that they came from and most commercial mistletoe is grown either on apples or poplars. A bigger problem is that mistletoe is usually cut before the berries are fully ripe so your Christmas sprig may not be any good for establishing your own clumps. But you have nothing to lose so in the New Year take your withered sprig and either make some cuts in the bark of your chosen tree and push the berries into them and hope for the best or just push the berries into natural fissures. You may have your own plants in a few years.


Long time, no see

For regular visitors, I apologise for the lack of posts over the past month. I was going to write about what was bothering me but it all seemed to pointless. Apart from some personal circumstances, the world was getting me down! When factual events are more unlikely than fiction and satire loses its sting because it is more real than reality I am lost for words. I managed to avoid making any comments, which is something in itself, but I could not bring myself to write anything about gardening either! Normal service has been resumed on this tiny piece of the web (I hope) even if nowhere else.



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6 Comments on “A-Z of botany: Parasite”

  1. derrickjknight
    December 10, 2016 at 11:00 am #

    Good to see you back, Geoff

  2. Anne Cullen
    December 10, 2016 at 12:52 pm #

    You were missed.
    Good to have you back
    Take care

  3. Kathy Larson
    December 10, 2016 at 2:35 pm #

    Glad to have you back.Believe me that your American cousins are just as devastated-at last count 2.8 million more of us voted Democrat.A dark road ahead,but the opposition is strong and united!

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