One of the most well known plants associated with the Druids is the Mistletoe (Viscum Album), yet what do we really know about this plant and it's connection to the Celts and their priests?
Well, the main source of our knowledge connecting the two is Pliny the Elder who writes about it in his Natural History. For the sake of completeness I am going to include everything Pliny said about the Mistletoe here:
"Chapter 95: Historical Facts Connected with the Mistletoe.
Upon this occasion we must not omit to mention the admiration that is lavished upon this plant by the Gauls. The Druids--for that is the name they give to their magicians -- held nothing more sacred than the mistletoe and the tree that bears it, supposing always that tree to be the robur. Of itself the robur is selected by them to form whole groves, and they perform none of their religious rites without employing branches of it; so much so, that it is very probable that the priests themselves may have received their name from the Greek name for that tree. In fact, it is the notion with them that everything that grows on it has been sent immediately from heaven, and that the mistletoe upon it is a proof that the tree has been selected by God himself as an object of his especial favour.
The mistletoe, however, is but rarely found upon the robur; and when found, is gathered with rites replete with religious awe. This is done more particularly on the fifth day of the moon, the day which is the beginning of their months and years, as also of their ages, which, with them, are but thirty years. This day they select because the moon, though not yet in the middle of her course, has already considerable power and influence; and they call her by a name which signifies, in their language, the all-healing. Having made all due preparation for the sacrifice and a banquet beneath the trees, they bring thither two white bulls, the horns of which are bound then for the first time. Clad in a white robe the priest ascends the tree, and cuts the mistletoe with a golden sickle, which is received by others in a white cloak. They then immolate the victims, offering up their prayers that God will render this gift of his propitious to those to whom he has so granted it. It is the belief with them that the mistletoe, taken in drink, will impart fecundity to all animals that are barren, and that it is an antidote for all poisons. Such are the religious feelings which we find entertained towards trifling objects among nearly all nations."
So from this we can learn that the Gaulish Druids that Pliny was writing about considered the oak sacred and the mistletoe which grew upon it to be divinely given, possibly because of its rarity. Whenever mistletoe in oaks was found it would then be gathered with due ceremony on the next appropriate day, which appears to be just before the first quarter of the moon, when, as Pliny says, the moon has power and influence. To me this is another interesting celestial connection with the mistletoe. The misteltoe would then be gathered with great ceremony, including a feast and the sacrifice of two bulls. Pliny also mentions the use of a golden sickle, however gold is far too soft to be used in a cutting tool - many people assume then that the sickle must have been of iron but since there were also prohibitions in later Celtic folklore about cutting herbs with cold iron I rather think it is more likely that the sickle was bronze, perhaps inlaid or coated with gold. (Incidently Pliny notes, as does Caesar in his Gallic Wars, that the Celts measured time by nights instead of days and began months and years also in such a way.)
The Mistletoe itself is a parasitic plant that grows in trees, rooting from seeds usually spread by birds. It grows to form a mass of twigs and leaves about 2 to 3 feet wide, flowers in May and produces berries between late Novemeber and December which are a waxy white in color. There is some debate about when the Druids may have collected Mistletoe, as some folkloric accounts mention it being gathered around new years (although whether this means Samhain or January 1st is unclear) although it would seem logical that the easiest time to gather it would have been in the fall or winter. As the book The Trees of Old Engalnd says "In summer we seldom notice that mistletoe is concelaed within the foilage of the tree it inhabits, not until autumn has stripped all away, and winter has rendered the woods transparent...do we discover its presence." Our only firm account of Druids harvesting mistletoe is Pliny and he makes no mention at all of the time of year or season, but does say that it was gathered whenever it was found, leading me to believe that there was no specific seasonal rite relating to it. I think it is possible that the later idea of the Druids collecting mistletoe at new years may have been a confusion of Pliny including a reference to the Celtic days, months and years beginning with the new moon with his discussion of the mistletoe being collected. Folklore associates Mistletoe with protection from all evil influences and it is also a symbol of fertility, something that is mentioned in Pliny's account, and may lend itself to the folk belief of kissing under the mistletoe. Additionally the stem and leaves had a wide variety of medicinal uses that can be documented back at least 500 years, and in folklore and practice longer. Culpepper's herbal from the 1600's mentions "Tragus saith, that the fresh wood of many mistletoe bruised, and the juice drawn forth and dropped in the ears that hath imposthumes in them doth help to ease them within a few days". According to Grieve's Modern Herbal mistletoe has been written about as a folk remedy in France and Britain since at least 1682. The stem and leaves - collected before the berries form - are used and it was believed to treat epilepsy and calm nervous disorders and treat heart conditions. It is noted that the berries have the opposite effect and are not recommended for use, although external use of the berries as a paste is mentioned. The berries are toxic and produce extreme intestinal discomfort, seizures, delirium, and heart problems in high doses.
The true connection between the Druids and mistletoe may always be something of a mystery, but it does seem that it played a role in Gaulish and possibly British belief and practice (not existing in Ireland). Examining the evidence we do have, thin as it may be, is none the less interesting and enlightening and shows us the possible reverence of a plant that was born of the sky and blessed by the gods, connected to a sacred tree, and with known healing applications.