Viscum album is a species of mistletoe in the family Santalaceae, commonly known as European mistletoe, common mistletoe or simply as mistletoe (Old English mistle). It is native to Europe and western and southern Asia.
Viscum album is a hemiparasite on several species of trees, from which it draws water and nutrients. It has a significant role in European mythology, legends, and customs. In modern times, it is commonly featured in Christmas decoration and symbology. (V. album is found only rarely in North America, as an introduced species; its cultural roles are usually fulfilled by the similar native species Phoradendron leucarpum.)
Description
It is a hemi-parasitic evergreen shrub, which grows on the stems of other trees. It has stems long with dichotomous branching. The leaves are in opposite pairs, strap-shaped, entire, leathery textured, long, broad and are a yellowish-green in colour. This species is dioecious and the insect-pollinated flowers are inconspicuous, yellowish-green, diameter. The fruit is a white or yellow berry containing one (very rarely several) seed embedded in the very sticky, glutinous fruit pulp.
It is commonly found in the crowns of broad-leaved trees, particularly apple, lime (linden), hawthorn and poplar.
European mistletoe is the only multicellular organism to not have a functioning respiratory complex I in its electron transport chain, a protein that's essential for the creation of useful energy for its cells. It is believed to survive by obtaining adenosine triphosphate and energy-rich compounds from its host as well as reorganizing its other respiratory complexes and slowing its growth and energy requirements.
Classification
The mistletoe was one of the many species originally described by Linnaeus. Its species name is the Latin adjective albus "white". It and the other members of the genus Viscum were originally classified in the mistletoe family Viscaceae, but this family has since been sunk into the larger family Santalaceae.
Subspecies
Several subspecies are commonly accepted. They differ in fruit colour, leaf shape and size, and most obviously in the host trees utilised. Viscum album subsp. abietis (Wiesb.) Abromeit. Central Europe. Fruit white; leaves up to . On Abies. Viscum album subsp. album. Europe, southwest Asia east to Nepal. Fruit white; leaves . On Malus, Populus, Tilia, and less often on numerous other species, including (rarely) Quercus. Viscum album subsp. austriacum (Wiesb.) Vollmann. Fruit yellow; leaves . Central Europe. On Larix, Pinus, Picea. Viscum album subsp. meridianum (Danser) D.G.Long. Southeast Asia. Fruit yellow; leaves . On Acer, Carpinus, Juglans, Prunus, Sorbus. Viscum album subsp. creticum has recently been described from eastern Crete. Fruit white; leaves short. On Pinus brutia. Viscum album subsp. coloratum Kom. is treated by the Flora of China as a distinct species Viscum coloratum (Kom) Nakai.
Toxicity
European mistletoe is potentially fatal, in a concentrated form, and people can become seriously ill from eating the berries.
The toxic lectin viscumin has been isolated from Viscum album. Viscumin is a cytotoxic protein (ribosome inactivating protein, or RIP) that binds to galactose residues of cell surface glycoproteins and may be internalised by endocytosis. Viscumin strongly inhibits protein synthesis by inactivating the 60 S ribosomal subunit. The structure of this protein is very similar to other RIPs, showing the most resemblance to ricin and abrin.
Some birds have immunity to the poison and enjoy the berries, especially the mistle thrush which is named for its favourite food.
Culture, folklore and mythology
European mistletoe features in many myths and legends from early written sources, into the modern period. In cultures across pre-Christian Europe, mistletoe was often seen as a representation of divine male essence (and thus romance, fertility and vitality).
Ancient Greek and Roman
Mistletoe figured prominently in Greek mythology, and is believed to be the Golden Bough of Aeneas, ancestor of the Romans. Also in Greek mythology mistletoe was used by heroes to access the underworld. The Romans associated mistletoe with peace, love and understanding and hung it over doorways to protect the household.