Viscum album

Viscum album is a species of mistletoe in the family Santalaceae, commonly called European mistletoe, common mistletoe, or simply mistletoe (Old English mistle). It is native to Europe, as well as western and southern Asia. V. album is found only rarely in North America, as an introduced species. 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 among Christmas decorations and symbology. In North America its cultural roles are usually fulfilled by the similar native species, Phoradendron leucarpum. Long used in alternative medicine traditions without any academic basis, mistletoe now is under study for pharmaceutical uses in modern medicine.

Description It is a hemi-parasitic evergreen shrub, which grows on the stems of other trees. The plant contains a haustorium that connects it to the host tree by connecting the xylem and phloem of the mistletoe to that of the host tree, which allows it to receive nutrients and water. It has stems 30–100 centimetres (12–39 in) long with dichotomous branching. The leaves are in opposite pairs, strap-shaped, entire, leathery textured, 2–8 centimetres (0.79–3.15 in) long, 0.8–2.5 centimetres (0.31–0.98 in) broad and are a yellowish-green in colour. This species is dioecious and the insect-pollinated flowers are inconspicuous, yellowish-green, 2–3 millimetres (0.079–0.118 in) diameter. The fruit is a white or yellow berry, and except for very rarely, containing one 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 known to lack a functioning respiratory complex I in its electron transport chain, a protein that is 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 the Swedish scientist 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 reclassified 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 used.

Viscum album subsp. abietis (Wiesb.) Abromeit. Central Europe. Fruit white; leaves up to 8 centimetres (3.1 in). On Abies. Viscum album subsp. album. Europe, southwest Asia east to Nepal. Fruit white; leaves 3–5 centimetres (1.2–2.0 in). On Malus, Populus, Tilia, and less often on numerous other species, including (rarely) Quercus. Viscum album subsp. austriacum (Wiesb.) Vollmann. Fruit yellow; leaves 2–4 centimetres (0.79–1.57 in). Central Europe. On Larix, Pinus, Picea. Viscum album subsp. meridianum (Danser) D.G.Long. Southeast Asia. Fruit yellow; leaves 3–5 centimetres (1.2–2.0 in). 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.

Distribution and habitat

Genetics The European mistletoe has one of the largest genomes of all organisms, at about 90 billion base pairs (compared to ~3 billion bp in the human genome). It encodes 39,092 distinct open reading frames encoding 32,064 proteins.

Toxicity

If ingested in a concentrated form, such as a herbal tea infusion, European mistletoe is potentially fatal. Otherwise, people have been known to 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 toxin and enjoy the berries, especially the mistle thrush that is so named because mistletoe is their favourite food. Birds are especially important in distributing the seeds of the plant to new locations in the trees in which it will grow.

Cultural 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. In Ancient Greek mythology, mistletoe was used by heroes to access the underworld. The Romans associated mistletoe with peace, love, and understanding. They hung mistletoe over doorways to protect the household.

Celtic

Pliny the Elder makes an account in his Natural History about the Celtic religious Ritual of oak and mistletoe, in which druids would climb oak trees to cut down the mistletoe growing on it where it would then be turned into an elixir said to cure infertility and the effects of poison

… excerpt ends here. Continue reading the full article.