Monday, December 23, 2013

Mistletoe...About It

I've been working on my photo collection and came across this mistletoe image (below) I'd taken about a year and half ago. It took quite a while to identify this plant (had some help). Since I know of, but never decorated with mistletoe during the Christmas season, I did some investigating to discover some natural history and culture behind this plant.
American Dwarf-mistletoe (Arceuthobium americanum)

My photo is of an American Dwarf-mistletoe (Arceuthobium americanum); it's not the species that folks traditionally associate with Christmas. In Europe, it's European mistletoe (Viscum album...the only species there) or here in North America, American Mistletoe (Phoradendron serotinum...is one of ~240 species in North America!). Tropical and subtropical areas of the planet have many more "mistletoe" species. All mistletoe species are parasitic on shrubs and trees; they are dependent on moisture and minerals from the host. They are photosynthetic and produce seeds. Many species are specific to a certain species as host.
The species I photographed is usually only found on Lodgepole pine (Pinus contorta). The four species of Dwarf-mistletoe in Montana are all very small, only 1-8 cm in length, as the name implies, and each occur on different species of conifer (USFS publication on conifer mistletoes). Conversely, American Mistletoe is not tied to a specific species of deciduous or coniferous plant for a host and it is much bigger, basketball sized in some cases. It can really be evident in winter when going through a leafless, oak forest. In cases it looks very unhealthy for the tree. According to references most trees are not killed outright by mistletoe, but productivity of the tree suffers. A pdf leaflet from the University of Georgia Warnell School of Forestry and Natural Resources has extensive information on mistletoe infection in trees.
David M. Watson (publication title: MISTLETOE—A KEYSTONE RESOURCE IN FORESTS AND WOODLANDS WORLDWIDE) found that mistletoe may in fact be a keystone species: "Species from 66 families of birds and 30 families of mammals have been recorded consuming mistletoe, spanning 12 and 10 orders..."  Over 240 species of Australian birds nest in mistletoe. So, it does not appear to be so bad ecologically.
For people, mistletoe has real and/or mythic properties. According to Wikipedia, herbalists use mistletoe for circulatory and respiratory ailments. Vitality and fertility are ascribed to the plant because it was once not understood how the plant spread, i.e. it would "magically" sprout on different trees without a seen process. It is guessed this is how the cultural tradition of "kissing" under the mistletoe evolved...this behavior noted in a 1808 newspaper ad!