The parasitic European Mistletoe, Viscum album, thrives on fruit trees such as the domestic apple tree and also other hosts such as lime, poplar, and hawthorn. Its heartland is the counties of Somerset, Gloucestershire, Herefordshire, and Worcestershire. However, since the mistletoe’s main habitat, the traditional orchards, have declined dramatically in the past 60 years, there is a looming threat that, in twenty years, yuletide revellers would have to import mistletoe from mainland Europe (a trend which has been, nonetheless, slightly increasing over the past few years). The solution offered by the National Trust is to purchase mistletoe from ‘sustainable home or local’ sources. The charity, in association with Natural England, had also launched a project last year which aims at restoring traditional orchards supporting small cottage industries. It must be mentioned that a common end effect of mistletoe infestation (apart from reduced growth) is death for the host and it remains to be seen how many traditional orchard owners would be keen on not excising the mistletoe bunches in their trees.
Mistletoe has a degree of ecological importance for it is an ecological keystone species (Watson, 2001). Since the plant provides food (especially during winter) and habitat for wildlife, it could be considered as having a positive effect on biodiversity.
The plant is also believed to have medicinal properties: lowering blood pressure and heart rate, easing anxiety, relieving headaches, improving concentration ability, and in the treatment of cancer (Ernst et al, 2003). In Germany, more than US $30 million is spent on mistletoe extracts, with a yearly sales increase of 20%.
Mistletoe’s anti-cancer properties remain a bone of contention (Ernst et al, 2003; Horneber et al, 2008). For instance, there are positive results (such as Hajto et al demonstrating that mistletoe’s ß-Galactoside-specific Lectin activated monocytes in the peripheral human blood, resulting in the secretion of Tumor Necrosis Factor a, Interleukin 1, and Interleukin 6, all of which can inhibit tumour growth; or, Büssing et al’s results which suggests that it could be used in the treatment of lymphoma and lymphocytic leukemia due to its property of inducing apoptosis in human lymphocytes), as well as negative (Steuer-Vogt et al, 2001; Gabius et al 2001). An exhaustive review of all randomised clinical trials (Ernst et al, 2003) illustrated that the published work had failed to demonstrate the efficacy of this therapy in cancer patients –in fact, it even had the potential to cause harm (as seen in Gabius et al’s study in which clinically relevant low doses of mistletoe lectin where shown to stimulate tumour proliferation in cell lines and histotypic cultures). Furthermore, there are grave concerns since lectins tend to sediment the erythrocytes.
Reverting to the gist of this post, our mango trees (here in Trivandrum, Kerala) have mistletoes (Loranthus sp) as well. And despite the unwelcome visitor’s virtues, we tend to care more about the potential mangoes, and hence excise the sprigs- and never fail to admire its tenacity when it springs back to life. In any case, due to the lack of a market for mistletoes in the country, there isn't any utility in retaining/cultivating these except during the Advent tradition of hanging up the mistletoe (and are probably a minority in following this tradition in the region). Ergo, I would to like to know the stance of the ‘traditional orchard’ owners. And, admittedly, during my years in Oxbridge (+London), I've noticed far more mistletoe in other trees than in apple.
Nonetheless, one does hope that the National Trust’s information on the mistletoe’s impending doom in the UK isn’t a case of crying wolf. Or is it indeed a legitimate concern?
Photo credit: sumeja
Horneber MA, Bueschel G, Huber R, Linde K, & Rostock M (2008). Mistletoe therapy in oncology. Cochrane database of systematic reviews (Online) (2) PMID: 18425885
Ernst E, Schmidt K, & Steuer-Vogt MK (2003). Mistletoe for cancer? A systematic review of randomised clinical trials. International journal of cancer. Journal international du cancer, 107 (2), 262-7 PMID: 12949804
Gabius HJ, Darro F, Remmelink M, André S, Kopitz J, Danguy A, Gabius S, Salmon I, & Kiss R (2001). Evidence for stimulation of tumor proliferation in cell lines and histotypic cultures by clinically relevant low doses of the galactoside-binding mistletoe lectin, a component of proprietary extracts. Cancer investigation, 19 (2), 114-26 PMID: 11296616
Steuer-Vogt MK, Bonkowsky V, Ambrosch P, Scholz M, Neiss A, Strutz J, Hennig M, Lenarz T, & Arnold W (2001). The effect of an adjuvant mistletoe treatment programme in resected head and neck cancer patients: a randomised controlled clinical trial. European journal of cancer (Oxford, England : 1990), 37 (1), 23-31 PMID: 11165126
Watson, DM (2001), Mistletoe-A Keystone Resource in Forests and Woodlands Worldwide, Annual Review of Ecology and Systematics 32, pp.219-249.
Büssing A, Suzart K, Bergmann J, Pfüller U, Schietzel M, & Schweizer K (1996). Induction of apoptosis in human lymphocytes treated with Viscum album L. is mediated by the mistletoe lectins. Cancer letters, 99 (1), 59-72 PMID: 8564930
Hajto, T., Hostanska, K., Frei, K., Rordorf, C., and H-J Gabius (1990). Increased Secretion of Tumor Necrosis Factor a, Interleukin 1, and Interleukin 6 by Human Mononuclear Cells Exposed to ß-Galactoside-specific Lectin from Clinically Applied Mistletoe Extract1. Cancer Res 50, pp. 3322