"In the case of the mistletoe, which draws its nourishment from certain trees, which has seeds which must be transported by certain birds...Its is therefore, of the highest importance to gain a clear insight into the means of modification and coadaptation."
Darwin (1859) - Origin of species
Mistletoes are aerial parasitic plants of shrubs and trees. To be more precise, they belong to the Sandalwood order (Santalales) in which only part (5) of the eighteen families developed the aerial parasitism (Nickrent, 2011). All species of mistletoe invade the xylem of hosts using a modified root called haustorium, being able to photosynthesize. Because of that, they are only half parasites - hemiparasites.
In Brazil, mistletoes are called “ervas-de-passarinho”. Something likes bird’s herb. Birds, indeed, are their main seed dispersers, eating the fruits and regurgitating, defecating of bill wiping the seeds onto tree branches. Mistletoes may also be dispersed through autochory (as in Arceuthobium), or by mammals, as in Tristerix corymbosus, solely dispersed by the marsupial Dromiciops gliroides in Argentina and Chile (Amico and Aizen, 2000).
As parasitic plants, unsuspecting people may think mistletoes are ugly creatures, which exists only to cause harm to their hosts. However, according to Dr. David Watson (Charles Sturt University, Australia), they are more Dryad than Dracula, acting as facilitators for other plants and offering food and shelter for fauna, including insects, spiders, birds, mammals and many others (Watson, 2009, 2001). Besides that, recent studies have shown that mistletoes also produce a nutrient-enriched litter, which is a precious source of minerals for plants in some soil-poor ecosystems (March and Watson, 2007).
Complexity is in the details. A host infected by a mistletoe, which hosts the eggs of a butterfly, which are being infected by a tiny parasitoid wasp.
Amico, G., Aizen, M.A., 2000. Mistletoe seed dispersal by a marsupial. Nature 408, 929–930.
March, W.A., Watson, D.M., 2007. Parasites boost productivity: Effects of mistletoe on litterfall dynamics in a temperate Australian forest. Oecologia 154, 339–347.
Nickrent, D.L., 2011. Santalales (Including Mistletoes), in: Encyclopedia of Life Sciences. John Wiley & Sons, Ltd, Chichester, UK, pp. 1–6.
Watson, D.M., 2009. Parasitic plants as facilitators: More Dryad than Dracula? J. Ecol. 97, 1151–1159.
Watson, D.M., 2001. Mistletoe—A keystone resource in forests and woodlands worldwide. Annu. Rev. Ecol. Syst. 32, 219–249.