Some similarities to :
Witches' Broom which is a gall on
Hornbeam and also on Wild Cherry (Gean) trees trees usually caused by the fungus Taphrina betulina which look rather like birds nests, but they are usually more dense than is Mistletoe.
Uniquely identifiable characteristics
Distinguishing Feature :
Mistletoe is dioecious, with male and female flowers on separate plants, the sticky white berries only appearing (between November to December) on female plants. The berries are eaten by Mistle Thrush birds as well as by other birds, but they are so sticky that they also stick to the birds beak as they try to eat them from where they are ready to be implanted on the next high branch of a tree that the bird visits. Because birds prefer to be high up in the trees, Mistletoes is to be mostly found near the top of the tree. But Mistletoe will only take on first or second year tree growth, and even then can take a whole year to 'root' and establish a connection with the host tree before it can obtain nutrients and fluids. Before that first year is up, it is on its own.
Mistletoe is Hemi-parasitic and grows on, obtaining some nutrients from, deciduous trees, especially Malus (
Apple), Populus (especially
Black Poplar), Tilia (
Lime) and Crataegus (
Hawthorn). Only rarely ever on Quercus (
Oak). It is grown commercially on mainly Apple Trees in orchards for the Christmas trade in mistletoe for kissing under. It is capable of photosynthesis itself but draws water and minerals from its host vascular system at distinct swellings or gall where the two conjoin.
Out of several sub-species found in the World, only the 'parent' grows in the UK, Viscum album. It contains a toxic protein and lectin called
Viscumin which has a high molecular weight. Other sources make mention of
viscotoxin as one of the toxins. They are, like Ricin, a RIP, a Ribosome Inactivating plant Protein which is another poisonous lectin, although the two target and bind to differing sites. Although Mistletoe is poisonous, fatalities are rare. It is concentrated in the white berries but is said to be present in the whole plant.
Mistletoe does, of course, contain other chemical compounds, but because Mistletoes can grow on a wide variety of differing trees and is hemi-parasitic on them, obtaining some nutrients from them, the composition and proportions of these secondary metabolites can vary. However, any toxicity of these compounds will probably pale into insignificance compared to the toxicity of the viscotoxins. A new acyclic monoterpene diglycoside has been found in Mistletoe, but it lacks a common name and the chemical name is very long.
Its greatest population density in the UK is in Somerset and Devon with a very broad spread around the home counties and a smaller outbreak on the Mid-Wales border. Virtually no presence north of South Yorkshire apart from one or two hectads.