by Bob Thomas
The leafless winter season typically elevates one’s awareness of mistletoe. Our local species is Phoradendron tomentosum.
Mistletoe and Christmas have a long tradition that extends back to ancient civilization in Europe, with the Druids having many customs associated with their mistletoe species. Our mistletoe tradition is that one gets a kiss if one stands under the plant. It is common for people around the world to hang it in their homes, especially during the Christmas season.
The origin of the name appears to be from the Anglo-Saxon words mistel (meaning dung) and tan (meaning twig). It was called “misteltan” and was believed to magically emerge where birds’ droppings appear on limbs.
The entire plant is green and somewhat leathery, with tiny white hairs covering its leaves and its brittle stems. The plant anchors to a host plant and its roots invade the host.
True parasitism is a form of symbiosis in which one species benefits to the detriment of its host species. Mistletoe extracts water and minerals from its host, but it manufactures its own sugars via photosynthesis. Over infestation can kill the host plant, but that is rare. Usually mistletoe’s presence simply reduces the vitality of the host. This combination of partial parasitism and partial self-reliance makes mistletoe a hemiparasite.
Mistletoe flowers are not showy, and are found in the forks of the mistletoe’s branches. Its white fruit are drupes. Just like a peach, cherry or plum, the mistletoe drupe has an outer skin (the exocarp), a fleshy zone (mesocarp), and a hard container that contains the seed (endocarp). The endocarp protects the seed as it passes through a bird’s digestive system.
Birds, notably Cedar Waxwings, American Robins, Hermit Thrushes, and Eastern Bluebirds in our area, are known to eat the fruit. Birds are very important in distributing seeds of mistletoe by either anointing limbs with their seed bearing droppings or by wiping the sticky seeds onto a limb as they cleanse their beaks. This sticky material that surrounds the seeds, called viscin, hardens in the air and firmly attaches the seed to its new home.
It seems to be common knowledge that “mistletoe berries are poisonous to humans,” but they are not so dangerous to humans that we should be overly concerned.
Mistletoe juices of various types have long figured in biochemical research. Some interesting proteins, called phoratoxins, show promise as a possible treatment for such human maladies as breast cancer. A review of the medical literature suggests that mistletoe is emerging as something more than an excuse for a kiss.