Mistletoe

1. Mistletoe A Special Lesson Produced by: Joan Jackson & Dr. Frank B. Flanders Georgia Agricultural Education Curriculum Office April 2002 Teachers should view notes pages for additional information on certain slides. View note pages by clicking on ‘View’ and then ‘Notes Page’ Click HERE for more information about the authors.

2. Introduction to Mistletoe • Mistletoe is one of our best-known, but least understood plants. Although, familiar to everyone at Christmas, with a history in folklore and legend, little is known about this strange plant other than kissing under the mistletoe as a Christmas tradition.

3. Mistletoe is a Vampire • It survives by sucking nutrients from the host tree, sometimes killing the tree although mistletoe has a vested interest in keeping the tree alive. For this reason, mistletoe is sometimes known as “the vampire plant.”

4. Mistletoe is a Freeloader • It is parasitic on the stems of woody plants, from which it derives water, mineral nutrients, and organic compounds carried in xylem sap.

5. Mistletoe is a Thief • It’s scientific name, Phoradendron, means “thief of the tree” in Greek. The mistletoe plant puts its roots down into tree limbs in order to steal water and nutrients. Mistletoe is semi parasitic; that is, it has green leaves that provide some energy meets many of its energy by sucking the life blood from its host, usually oaks, elms, and poplars.

6. What is Mistletoe? • The well-known Mistletoe is an evergreen parasitic plant, growing on the branches of trees, where it forms pendent bushes, 2 to 5 feet in diameter.

7. What is Mistletoe cont. • Evergreen clumps of mistletoe are readily observed on deciduous trees in winter when leaves are off the trees.

8. What is Mistletoe cont. • Mistletoe is especially interesting botanically because it is a partial parasite (a “hemi parasite”). As a parasitic plant, it grows on the branches or trunk of a tree and actually sends out roots that penetrate into the tree to take up nutrients. But mistletoe is also capable of producing its own nutrients by photosynthesis.

9. What is Mistletoe cont. • American mistletoe (Phoradendron species) can be found growing in deciduous trees from New Jersey and southern Indiana southward to Florida and Texas. It is also the state flower of Oklahoma.

10. What is Mistletoe cont. • Most of the mistletoe sold during the holiday season is gathered in the wild. Most mistletoe is harvested in Oklahoma and Texas.

11. How did Mistletoe get its Name? • The common name of mistletoe is derived from the ancient belief that mistletoe was propagated from bird droppings. This belief was related to the then-accepted principle that life could spring spontaneously from dung.

12. How did Mistletoe get its Name? cont. • It was observed in ancient times that mistletoe would often appear on a branch or twig where birds had left droppings. “Mistel” is the Anglo-Saxon word for “dung,” and “toe” is the word for twig. So, mistletoe means “dung-on-a-twig.”

13. The Sex of Mistletoe • Mistletoe plants are either male (produce only pollen) or female (produce berries).

14. The Sex of Mistletoe cont. • All species of mistletoe in the United States are dioecious meaning they have male and female flowers on separate plants. Male plants produce only pollen, and female plants produce flowers and fleshy, white seed pods. Each pod is filled with a slimy and sticky clear fluid and one seed covered with a tough greenish membrane (see photos below).

15. Why is mistletoe green if it is parasitic? • Technically speaking, mistletoe is a semi-parasite, although it steals water and nutrients from a host plant. It has green leaves from chloroplasts used in photosynthesis. • Mistletoe plants develop well in full sunlight and reach most extensive development high in the crowns of large trees where it can obtain the light needed for photosynthesis.

16. Legends and Traditions • The traditions, which began with the European mistletoe in ancient times, were transferred to the similar American plant with the process of immigration and settlement.

17. Legends and Traditions cont. • In the Middle Ages and later, branches of mistletoe were hung from ceilings to ward off evil spirits. In Europe they were placed over house and stable doors to prevent the entrance of witches.

18. Legends and Traditions cont. • In Scandinavia, mistletoe was considered a plant of peace, under which enemies could declare a truce or disagreeing spouses could kiss and make-up.

19. Legends and Traditions cont. • In some parts of England the Christmas mistletoe is burned on the twelfth night lest all the boys and girls who have kissed under it never marry.

20. Legends and Traditions cont. • Kissing under the mistletoe is first found associated with the Greek festival of Saturnalia and later with primitive marriage rites. Mistletoe was believed to have the power of bestowing fertility, and the dung from which the mistletoe was thought to arise was also said to have “life-giving” power.

21. Legends and Traditions cont. • And for those who wish to observe the correct etiquette: a man should pluck a berry when he kisses a woman under the mistletoe, and when the last berry is gone, there should be no more kissing!

22. Legends and Traditions cont. • In the first century, the Druids in Britain believed that mistletoe could perform miracles, which ranged from providing fertility to humans and animals to healing diseases and protecting people from witchcraft.

23. Legends and Traditions cont. • The Druids believed mistletoe could influence human fertility and was prescribed to individuals who had problems bearing children. Mistletoe has also been used in medicine as treatment of pleurisy, gout, epilepsy, rabies, and poisoning.

24. Traditions of Mistletoe cont. • Plastic mistletoe has become a fairly common substitute in recent years because real mistletoe has poisonous berries.  It's all part of the fun of Christmas, but some consider it a shame to devalue traditions by using fake material.

25. Traditions of Mistletoe cont. • Because of its association with pagan ceremonies, mistletoe was banned from Christmas ceremonies by the Church in Medieval times.

26. Traditions of Mistletoe cont. • A common medieval belief held that mistletoe was the wood used to make the crucifix.Cursed, mistletoe was no longer welcome on earth and was doomed to live as a parasite growing on trees. It was not until the 17th century that people became more open about their fondness for mistletoe.

27. What Genus/Species is Mistletoe? • The mistletoe that is commonly used as a Christmas decoration, genus Phoradendron flavescens, is native to North America.

28. What Genus/Species is Mistletoe? cont. • Phoradendron (American mistletoes) • There are some 1500 species of mistletoes worldwide. • Phoradendron is a large genus (perhaps 170 species) of primarily tropical and subtropical evergreen plants restricted to the Americas. Twelve species occur in the United States.

29. Seed Dispersal • The small, sticky, whitish berries are produced from October to December. American mistletoes are most often distributed by birds. Birds avoid the immature fruits which are bitter, hard and contain poisonous compounds. Instead, they eat mature fruits, however, they are still hard to digest.

30. Seed Dispersal cont. • The birds ingest the fruit and digest the pulp, but the seeds quickly pass through the intestinal tract, retaining a sticky covering of hair-like threads that serve as glue to adhere them to the surface on which the remaining seeds fall.

31. Seed Dispersal cont. • Another way birds spread seeds is when the birds clean their bills by rubbing them against the branches or bark of trees because the sticky seeds of mistletoe tend to cling to the bills of birds.

32. Seed Dispersalcont. • In most cases, the initial infestation occurs of mistletoe on larger or older trees because birds prefer to perch in the tops of tall trees.

33. Seed Dispersal cont. • While broadleaf mistletoe seeds are dispersed by birds, dwarf mistletoe seeds are spread mostly by their random forcible discharge from fruit, which can propel seeds horizontally into trees up to 30 to 40 feet away.

34. Seed Dispersal cont. • Seeds are capable of germinating anywhere if temperature and moisture are suitable, but only seeds that lodge on thin bark of twigs and small branches of a suitable host will cause infection.

35. Seed Dispersal cont. • A heavy buildup of mistletoe often occurs within an infested tree because birds are attracted to the berries, and may spend a significant amount of time feeding on them and depositing their droppings. In addition, seeds may fall from mistletoe plants in the upper part of the tree, creating new infestations on the lower branches.

36. Germination • Seeds are rapidly defecated by birds while they still have their slimy, sticky coating. This allows the seeds to cling to a branch, sprout and insert its root-like "haustoria" into the water-conducting system of the tree.

37. Germination cont. • Upon germination, the radical flattens itself against the bark, forming an attachment disc or holdfast. A multicellular projection called the primary haustorium grows from the undersurface of the holdfast and penetrates the bark, often through lenticels or auxiliary buds.

38. Germination cont. • It takes many years for mistletoe to grow large enough to produce flowers and seeds. The haustoria in mistletoe both penetrates the water-conducting tissue of the trees (water transport) and infiltrate in between the cells where they absorb most nutrients.

39. Germination cont. • Once beneath the periderm in living cortical tissue or secondary phloem, the primary haustorium produces a radiating system of branches termed cortical strands or cortical haustoria. Wedge-shaped projections called sinkers grow from the cortical strands and pass through the cambium to the outer surface of the lignified xylem.

40. Germination cont. • Certain cells within the sinker differentiate into water-conducting tracheids and vessels. Some of these come into intimate contact with vessels or tracheids of the host such that open pits and perforations connect the water-conducting systems of the two plants. This assures transport of water and minerals to the parasite.

41. Germination cont. • Activity of this meristem is synchronized with that of the host so that the sinker elongates as the host stem increases in radius.Aerial shoots begin to grow after the system of cortical stands and sinkers is initiated. The first shoots arise from buds on the holdfast, and they grow only a few millimeters during the first year.

42. Is Mistletoe Poisonous? • Some mistletoes are poisonous to humans, especially some of the true or leafy mistletoes of hardwood trees, but it typically takes ingestion of numerous leaves or shoots of a mistletoe plant to affect an adult. Children and pets on the other hand, are much smaller and are affected by much less of a plant.

43. Is Mistletoe Poisonous? cont. • Although mistletoe has been used in the treatment of several ailments, the berries are poisonous. Individuals using mistletoe during the holiday season should keep the sprigs out of the reach of children. For safety reasons, many companies have replaced the berries with artificial, plastic berries.

44. How does Mistletoe invade a tree? • After arriving on a host, a typical mistletoe seed's first exploratory root grows away from light, and into the crevices of the bark of a limb or tree trunk. Once inside the bark, the mistletoe sends in special wedge tissue in search of the plumbing.

45. How does Mistletoe invade a tree? cont. • Hitting the host's network of water-carrying cells deep inside the plant, the mistletoe builds its own system of ducts to steal water and nutrients. After the mistletoe seed germinates, it grows through the bark and into the tree's water-conducting tissues, where root-like structures called haustoria develop.

46. How does Mistletoe invade a tree? cont. • The haustoria gradually extends up and down within the branch as the mistletoe grows. Initially, the parasitic plant grows slowly; it may take years before the plant blooms and produces seeds. Broadleaf mistletoes have succulent stems that become woody at the base.

47. How does Mistletoe invade a tree? cont. • Initial infection usually occurs on a small branch and is followed by multiple infections on the same tree after the initial plant produces fruit. The dominant symptom caused by mistletoe is atrophy (meaning wither) and dieback of branch ends beyond the point of attachment of the parasite.

48. How does Mistletoe invade a tree? cont. • Mistletoe may increase dramatically within a single tree where birds roost, feed on berries, and deposit seeds on twigs and branches. Multiple infections result in loss of vigor, dieback, and often death (to the tree).

49. How does Mistletoe invade a tree? cont. • Bark tissues of host and parasite meet in a convoluted line at the swollen union. Dissection shows continuity of xylem of host and parasite.

50. How does Mistletoe invade a tree? cont. • Mistletoe has developed a very specialized tissue with the shape of a bell (called a haustorium). This bell-shaped structure grows into the host tree and combines with the living tree.