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Viscum album
- European mistletoe
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. (Viscum 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.)
It is a hemi-parasitic evergreen shrub, which
grows on the stems of other trees. It has stems 30-100 cm. (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 cm.
(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 mm. (0.079-0.118 in.) 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.
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 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.
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
Uses
Mistletoe is an ingredient of pomace brandy based
liquor biska, a type of
rakija made in
Istra, Croatia. The sticky juice of mistletoe berries was used to make birdlime,
an adhesive to trap small animals or birds.
Mistletoe leaves and young twigs are
used by herbalists, and preparations made from them are popular in
Europe, especially in Germany, for attempting to treat circulatory
and respiratory system problems. Use of mistletoe extract in the
treatment of cancer originated with Rudolf Steiner, the founder of
Anthroposophy. Although laboratory and animal experiments have
suggested that mistletoe extract may affect the immune system and be
able to kill some kinds of cancer cells, there is little evidence of
its benefit to people with cancer.
Bird trapping
The Latin word
viscum, 'mistletoe, birdlime' is
the source of viscous. |