Intriguing World of Weeds Mistletoe-the Christmas Weed1

LARRY W. MITICH2

INTRODUCTION flavescens (11) throughout the U.S. and P. serotinum in Mistletoe is unusual among the east (1). weeds: it is not often thought of as a The other U.S. genus, Arceuthobium, grows mostly 'weed' in the vernacular sense, and on pines. This genus was named by Friedrich August it is not listed in the WSSA's Com­ Marschall von Bieberstein (1768-1826) from the Greek posite List of Weeds. However, it arkeuthos, juniper, and bios, life (10). The arceutho­ fits our definition-a plant growing bia-commonly called dwarf mistletoes-have a seri­ where it is not wanted- and it fits ous impact on the American soft wood industry. the requirements of this column, The mistletoe of European fable is Viscum album L. (1). Viscum is Latin for 'bird-lime' (9), a sticky sub­ meaning it has a long and fascinat­ ing relationship with man. stance made from mistletoe berries and smeared on branches to catch small birds. Many Latin words sprang from this root, among them the forerunners of our TAXONOMY AND NAME HISTORY 'viscous' and 'viscosity.' Album is Latin for 'white,' Barlow defirtes "mistletoes" as shrubby parasites the usual color of this species' fruit. This plant was which grow attached to tree branches (3). Taxonomical­ described by Carolus Linnaeus in 1753. · ly, mistletoes are flowering plants which belong to one The word 'mistletoe' originated as misteltan in An­ of three families-Loranthaceae, Viscaceae, or glo-Saxon, from the diminutive of Gennan mist (dung) Eremolepidaceae (4). Representatives of two other fam­ and the Anglo-Saxon tan (twig). Apparently it was ilies have also independently adopted the mistletoe life observed early on that berry-eating birds play a crucial habit (4). part in distributing the seed of this plant (7). (The In traditional taxonomy, all mistletoes were placed in taxonomic name for the Mistie Thrush is Turdus vis­ the Loranthaceae - a name conjugated from the Latin civorus. As mentioned, Viscivorus means sticky. Any lorum, a thong or strap, and the Greek anthos, a flower guesses about the genus name?) Lestrange suggests that (9). Some authorities still take the view that other the prefix evolved from the Old Dutch mist (birdlime) mistletoe groups are merely subfamilies of the Loran­ or mistle (different-Le., different from the host tree) thaceae (4). (12). We are perhaps most familiar with species of the Viscaceae (named from the Latin word viscum, dis­ FOLKLORE AND MEDICINE cussed below). In this family are placed the two genera Viscum album was sacred to the Druids of northern native to the U.S. as well as the .genus Viscum, the Europe, the Ainos of Japan, and certain African tribes 'traditional' mistletoe used by ancient herbalists, wor­ (7). shipped by Druids, and ultimately described by Lin­ One story has it that the True Cross was made from naeus. mistletoe wood, and as punishment the plant was The genus Phoradendron comprises the mistletoes banned from the earth. Mistletoe is still called Herbe de found on deciduous trees in the United States. Thomas la Croix in parts of Brittany, and it has also been known Nuttal (1786-1859) named this genus from the Greek as lignum-crucia (12). (This reminds me very much of a phor, a thief, and dendron, a tree (10), in reference to similar story featuring dogwood.) the plant's parasitic habit. The mistletoes which sprout Other common names of the mistletoe include mislin in American doorways during the holiday season are P. bush, kiss and go, and churchman's greeting (12). Viscum album was the only mistletoe commonly used in medicine (12), but it appeared in the herbals of 1 No. 34 of the series "Intriguing World of Weeds." Contn'butions are western and central Europe, China, and the Middle welfme and will be acknowledged. Send contributions to Larry W. Milich. Bxt, Weed Sci,, I>ep, Bot,, VDiv, Calif,, Davis, CA 9S616, East. The Greek herbalist Dioscorides recommended

692 Weed Technology. 1991. Volume 5:6~94 WEBD TECHNOLOGY

pounding and moistening, or chewing, adhere to the feathers of birds nesting in mistletoe the fruit of Viscum album to make a plants and are carried about. Some birds eat the whole paste which would reduce swellings mistletoe fruits and regmgitate the seeds in pellets, but and infections (6). Pliny said mistletoe the seeds seldom, if ever, become established. Seed of was a cure for sterility and epilepsy, but fruits falling onto lower branches of trees is believed to to be effective it must not be allowed to be another form of dissemination (4). touch the ground (12); presumably he Mistletoe seed lack a seed coat, but instead are perceived the plant as charged with di­ covered with viscin, a mass of cellulolytic strands in a vine curative powers which could easily matrix of pectic substances (4). Viscin bonds the seed be discharged through casual handling. to the host and absorbs moisture. The seed of most species germinates in the spring, with the penetration DISTRIBUTION AND ECONOMIC IMPACT process requiring up to 6 weeks; the germinating radi­ cles (embryo tips) are negatively phototropic and ge­ Worldwide, mistletoe is represented by about 900 otropically neutral. Once contact is made with a host species in 65 genera of Loranthaceae, and 400 species surface, the radicular tip cells divide to form a in 7 genera of Viscaceae (3). The U.S. has only two haustorial disk (or holdfast), a loosely organized mound native genera. of tissue. The parasitic cells that come in contact with Mistletoes cause a great deal of damage in forests, the host surface have dense contents and large nuclei orchards, plantations, and omamen~ls worldwide. (4). They adhere to the host tissue, pulling apart host Hawksworth (8) states that mistletoes impair growth, peridenn and exposing living host cells. Abundant se­ lower host vigor, reduce wood quality and quantity, cretions harden eventually to form an air tight seal reduce fruiting, and predispose trees to attack by in­ between the host and parasite. Concurrently the sects, disease, and fungi. meristem of the parasite develops, becoming the In North America, the dwarf mistletoes (Arceutho­ penetration structure, which secretes a substance into bium spp.), which parasitize conifers, are responsible the cavity, enabling the endophyte to pass into the host. for most of the mischief. Estimates suggest these spe­ Tissue penetration undoubtedly involves enzymes and a cies cause annual wood losses of about 500 million mechanical force produced by growing and expanding cubic feet in the U.S. (13) and 150 million cubic feet in (4). British Columbia (2). Most, if not all, of the familiar mistletoe species are poisonous, containing the amines beta-phenylethyla­ BIOLOGY AND HABITAT mine and tyramine (11). Documented cases of poison­ Mistletoe is parasitic on trees----our native Phoraden­ ing include Phoradendron villosum killing 13 cattle of a dron mostly on deciduous trees, Arceuthobium on herd of 30 in California (14), though livestock usually conifers. It gains much of its mystique from the fact avoid the plant. Berries of Phoradendron species are that it is evergreen, often showing the only green in the usually considered poisonous, though Kingsbury (11) dead of winter in deciduous forests. reports only one confirmed fatality-a death following Mistletoe leaves are opposite, simple and entire, and consumption of tea brewed from the berries of P. leathery, sometimes reduced to scales. Its flowers are flavescens (5). greenish, inconspicuous, and without petals. The fruit is Viscum album, the mistletoe of European legend, is a berry with gluey fluid inside (10). also known to be poisonous (11). Mistletoe seed is disseminated by various methods and widely diverse agents. In Australia the major means LITERATURE CITED of dissemination is the defecation of mistletoe seed by 1. Bailey, L. H., and E. Z. Bailey. 1976. Hortus 'lbild. Macmillan birds (4). In some speci~s, the birds eat the fruits after Publishing Co., Inc., NY. discarding the epicarps, and then defecate the seeds on 2. Baranyay, J. A., and R. B. Smith. 1972. Can. Por. Serv. Rep. BC-X72. 3. Barlow, B. A. 1983. Biogeography of Lorantbaceac and Viscaceac. In their perch. Also some birds eat only the viscid pulp The Biology of Mistletoes, D. M. Calder and P. Bemhanlt, eds. and do not swallow the seeds. Many species of birds Academic Press Inc., NY. that feed on mistletoe remove the viscid seeds sticking 4. Calder, D. M. 1983. Mistletoes in focus: an introduction. In The Biology of Mistletoes, D. M. Calder and P. Bembardt, eds. Academic to their bills by wiping them off on a branch (4). Seeds Press Inc., NY.

Volume S, Issue 3 (July-September) 1991 693 MITICH

5. Cann, H. M., and H. L. Verhulst 1959. Toxic Hazards at Christmas. 10. Jepson, W. L. 1951. A Mauual of the Flowering Plants of California. Nat. Clearinghouse Pois. Contr. Cent. Univ. of Ca1ifomia Press, Berkeley. 6. Dioscorides. 1933. The Greek Herbal of Dioscorides. R. T. Gunther, 11. Kingsbury, 1. M. 1964. Poisonous Plants of the United States and ed. Hafner Publishing Co., Inc., NY. Canada. Prentice-Hall, Inc., Englewood Cliffs, NJ•. 7. Durant. M. 1976. Who Named the Daisy? Who Named the Rose? 12. LcStrange, R. 1977. A History of Herbal Plants. Angus and Robertson, Dodd, Mead and Co., NY. London. 8. Hawkswortb, F. O. 1980. Crop loss assessment Proc. B. C. Stakman 13. Shea, IC. R., and B. Howard. 1969. In Western forest pest conditions. Commemorative Symp. Univ. Minn. Bxp. Stn. Misc. Publ. 7. Proc. 59th Wcat. Por. and Conscrv. Assoc., p. 25--32. 9. Jaeger, B. C. 1944. A Source-book of Biological Names and Terms. 14. Wicktor, C. E. 1952. Poisonous Plants. In Annual Report 23, Los Charles C. Thomas, Springfield, IL. Angeles County Livestock Dep.

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ABSTRACTS (78 papers) $10.00 ea. Second International Symposium on Adjuvants for Agrichemicals

BIBLIOGRAPHY (approx. 65 pages) $20.00 ea. Formulations and Applications of Adjuvants for Agrichemicals: A selected Bibliography of World Literature in English (revised and updated, May 1989)

Individuals, agrichemical companies or other organizations who are interested in purchasing single or multiple copies of either or both of these publications may order directly from:

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694 Volume 5, Issue 3 (1ul)'-September) 1991