Mistletoe
European mistletoe has smooth-edged, oval, evergreen leaves borne in pairs along the woody stem, and waxy, white berries that it bears in clusters of two to six.
Over the centuries, the term mistletoe has been broadened to include many other species of parasitic plants with similar habits, found in other parts of the world, that are classified in different genera and families such as the Misodendraceae of South America and the mainly southern hemisphere tropical Loranthaceae.
[6] Online Etymology Dictionary claims a similar theory, noting: "The alteration of the ending... is perhaps from a mistaking of the final -n for a plural suffix after tan fell from use as a separate word, but Oxford finds it a natural evolution in West Saxon based on stress.
[11] Mistletoe species grow on a wide range of host trees, some of which experience side effects including reduced growth, stunting, and loss of infested outer branches.
Some species, such as Viscum capense, are adapted to semi-arid conditions and their leaves are vestigial scales, hardly visible without detailed morphological investigation.
Not only do they photosynthesize actively, but a heavy infestation of mistletoe plants may take over whole host tree branches, sometimes killing practically the entire crown and replacing it with their own growth.
It commonly has two or even four embryos, each producing its hypocotyl, that grows toward the bark of the host under the influence of light and gravity, and potentially each forming a mistletoe plant in a clump.
On having made contact with the bark, the hypocotyl, with only a rudimentary scrap of root tissue at its tip, penetrates it, a process that may take a year or more.
[12] Species more or less obligate include the leafless quintral, Tristerix aphyllus, which lives deep inside the sugar-transporting tissue of a spiny cactus, appearing only to show its tubular red flowers,[13] and the genus Arceuthobium (dwarf mistletoe; Santalaceae) that has reduced photosynthesis; as an adult, it manufactures only a small proportion of the sugars it needs from its own photosynthesis, but as a seedling actively photosynthesizes until a connection to the host is established.
Of the many bird species that feed on them, the mistle thrush is the best-known in Europe, the phainopepla in southwestern North America, and Dicaeum flowerpeckers in Asia and Australia.
[17] Once a mistletoe plant is established on its host, it usually is possible to save a valuable branch by pruning and judicious removal of the wood invaded by the haustorium, if the infection is caught early enough.
[20][21] The primary active toxic compounds in American mistletoe are phoratoxins (in Phoradendron) and their effects can include blurred vision, diarrhea, nausea, and vomiting, although these rarely occur.
[25] A broad array of animals depend on mistletoe for food, consuming the leaves and young shoots, transferring pollen between plants and dispersing the sticky seeds.
In western North America their juicy berries are eaten and spread by birds (notably the phainopepla) while in Australia the mistletoebird behaves similarly.
When eaten with the fruit, some seeds pass unharmed through their digestive systems, emerging in extremely sticky droppings which the bird deposits on tree branches, where some may stick long enough to germinate.
[citation needed] The dense evergreen witches' brooms formed by the dwarf mistletoes (Arceuthobium species) of western North America also make excellent locations for roosting and nesting of the northern spotted owl and the marbled murrelet.
[34] In the advent of the Christian era, mistletoe in the Western world became associated with Christmas as a decoration under which lovers are expected to kiss, as well as with protection from witches and demons.
[35] Mistletoe continued to be associated with fertility and vitality through the Middle Ages, and by the eighteenth century it had also become incorporated into Christmas celebrations around the world.
