''Phoradendron'' is a genus of

mistletoe Mistletoe is the common name for obligate parasite, obligate parasitic plant, hemiparasitic plants in the Order (biology), order Santalales. They are attached to their host tree or shrub by a structure called the haustorium, through which they ...

, native to warm temperate and tropical regions of the

Americas The Americas, sometimes collectively called America, are a landmass comprising the totality of North America and South America.''Webster's New World College Dictionary'', 2010 by Wiley Publishing, Inc., Cleveland, Ohio. When viewed as a sing ...

. The center of diversity is the

Amazon rainforest The Amazon rainforest, also called the Amazon jungle or Amazonia, is a Tropical and subtropical moist broadleaf forests, moist broadleaf tropical rainforest in the Amazon biome that covers most of the Amazon basin of South America. This basin ...

.Coder, K. D
American mistletoe (''Phoradendron serotinum'' var. ''serotinum'') infection in trees.
WSFNR08-25. Tree Health Series. University of Georgia. 2008. ''Phoradendron'' is the largest genus of mistletoe in the Americas, and possibly the largest genus of mistletoes in the world. Traditionally, the genus has been placed in the family

Viscaceae Viscaceae is a taxonomic family name of flowering plants. In this circumscription, the family includes the several genera of mistletoes. This family name is currently being studied and under review as in past decades, several systems of plant tax ...

, but recent genetic research acknowledged by the Angiosperm Phylogeny Group shows this family to be correctly placed within a larger circumscription of the

sandalwood Sandalwood is a class of woods from trees in the genus ''Santalum''. The woods are heavy, yellow, and fine-grained, and, unlike many other aromatic woods, they retain their fragrance for decades. Sandalwood oil is extracted from the woods. Sanda ...

family,

Santalaceae The Santalaceae, sandalwoods, are a widely distributed family of flowering plants (including small trees, shrubs, perennial plants, perennial herbs, and epiphyte, epiphytic climbersHewson & George t al.'Santalaceae'' taxonomy, 1984, pp. 191-1 ...

. They are woody hemi-parasitic

shrub A shrub or bush is a small to medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees by their multiple ...

s with branches long, which grow on other

tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, e.g., including only woody plants with secondary growth, only ...

s. The foliage is dichotomously branching, with opposite pairs of

leaves A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...

; these are fairly large, long, green and

photosynthetic Photosynthesis ( ) is a Biological system, system of biological processes by which Photoautotrophism, photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical ener ...

in some species (e.g. ''P. leucarpum''), but minimal in some others (e.g. ''P. californicum''). Although they are able to photosynthesize the plant relies on its host for some nutrients. The plant draws its mineral and water needs, and some of its energy needs, from the host tree using a haustorium which grows into the stems of the host. The

flower Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...

s are inconspicuous and incomplete, no petals and 3-4 greenish-yellow sepals, diameter. The

fruit In botany, a fruit is the seed-bearing structure in flowering plants (angiosperms) that is formed from the ovary after flowering. Fruits are the means by which angiosperms disseminate their seeds. Edible fruits in particular have long propaga ...

is a

berry A berry is a small, pulpy, and often edible fruit. Typically, berries are juicy, rounded, brightly colored, sweet, sour or tart, and do not have a stone or pit although many pips or seeds may be present. Common examples of berries in the cul ...

, white, yellow, orange, or red when mature, containing one to several

seed In botany, a seed is a plant structure containing an embryo and stored nutrients in a protective coat called a ''testa''. More generally, the term "seed" means anything that can be Sowing, sown, which may include seed and husk or tuber. Seeds ...

s embedded in very sticky juice, called viscin. The flowers are

unisexual Dioecy ( ; ; adj. dioecious, ) is a characteristic of certain species that have distinct unisexual individuals, each producing either male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproduction is ...

, and depending on the species, the plant will be monoecious or dioecious (both male and female flowers on a single plant or male and female plants with only one sex of flowers). The seeds are dispersed when

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

s eat the fruit and remove the sticky seeds from their bills by wiping them on tree branches where they can germinate. The foliage and berries of some species are toxic. Leafy mistletoes seldom kill but they cause stress reducing crop productions in fruits and nut trees. ''Phoradendron'' plants can be distinguished from mistletoes in other genera in Viscaceae by their

inflorescence In botany, an inflorescence is a group or cluster of flowers arranged on a plant's Plant stem, stem that is composed of a main branch or a system of branches. An inflorescence is categorized on the basis of the arrangement of flowers on a mai ...

s, which lack leaves and come from a single branching point or apical meristem. However, it can be difficult to identify species within ''Phoradendron,'' because leaf shape and color can vary greatly even within species. Phoradendron sp

Host and symptoms

''Phoradendron'' species can infest many taxa of plants including hackberry (''Celtis spp.'') mesquite (''Prosopsis spp.''), cedar, elm (''Ulmus spp.''), and Osage-orange.Turner, M. W. ''Remarkable Plants of Texas: Uncommon Accounts of our Common Natives''. University of Texas Press. 2009. pg. 261. Certain species of ''Phoradendron'' are host-specific; for example, in Arizona, ''Phoradendron tomentosum'' infests cottonwood (''Populus fremontii''), sycamore (''Platanus wrightii''), ash (''Fraxinus'' spp.), walnut (''Juglans'' spp.) and willow (''Salix'' spp.).Geils, B. W., et al
Mistletoes of North American conifers.
Gen. Tech. Rep. RMRS-GTR-98. Ogden, Utah: USDA, Forest Service, Rocky Mountain Research Station. 2002. ''P. californicum'' infests shrubs and trees such as acacia (''Acacia'' spp.) and blue palo verde (''Parkinsonia florida''). Some species infest junipers (''Juniperus'' spp.) and oaks (''Quercus'' spp.).Hine, R
Diseases of Urban Plants.
Adapted by M. Olsen. Plant Disease Publications. University of Arizona Cooperative Extension. Revised 1999. Branches often become swollen and distorted, forming

burl A burl (American English) or burr (British English) is a tree growth in which the grain has grown in a deformed manner. It is commonly found in the form of a rounded outgrowth on a tree trunk or branch that is filled with small knots from d ...

s and making the tree more susceptible to insect attack. ''Phoradendron'' presents serious problems along rivers, streams, parks, and golf courses with large cottonwood trees. Deciduous trees can be mistaken for evergreens during the winter if infection is heavy. Other common symptoms include swelling formations of witch's broom, dieback, and weakened branches.

Life cycle

''Phoradendron'' species are hemiparasites which produce their own chlorophyll but rely on the host plant to provide water, minerals, and other nutrients.Watson, W. T. and T. Martinez-Trinidad. (2006)
Strategies and treatments for leafy mistletoe (''Phoradendron tomentosum'' (DC.) Engelm ex. Gray) suppression on cedar elm (''Ulmus crassifolia'' Nutt.).
''Arboriculture and Urban Forestry'' 32(6) 265-70. Birds are the primary means of dispersal of the parasite. Birds consume the

drupe In botany, a drupe (or stone fruit) is a type of fruit in which an outer fleshy part (exocarp, or skin, and mesocarp, or flesh) surrounds a single shell (the ''pip'' (UK), ''pit'' (US), ''stone'', or ''pyrena'') of hardened endocarp with a seed ...

s of the mistletoe and excrete or regurgitate the seeds onto the branches of the host plant. The seeds do not need to be ingested to germinate. Germinating seeds produce a radicle, a holdfast, and eventually the germinated seeds produce haustoria. The haustorium is a root-like structure that penetrates the host plant's bark and cambium, reaching the xylem and phloem where it extracts water and minerals, primarily carbon and nitrogen compounds. A study on the nutrient ratio between ''Phoradendron'' and their hosts found that the parasite have higher concentrations of nitrogen and minerals, especially in leguminous hosts. This suggests that the parasite actively draws nutrients from the host plant through both the xylem and phloem, challenging the alternative theory of the passive uptake of nutrients by the parasite from the host xylem only. The most important birds for effective dispersal include the cedar waxwing, euphonias, silky-flycatchers, bluebirds, and thrushes.

Management

Leafy mistletoe can adversely affect trees growing in urban environments and in forests. It is considered a nuisance in urban environments because of its appearance on deciduous trees during winter. Severe colonization of mistletoe can affect the health of an individual tree, and a tree already stressed by other factors can be killed. Forest fragmentation can increase ''Phoradendron'' infection rates in some oak trees, as trees in lower density forests and those closer to the forests' edges are more likely to be colonized by the mistletoe. Control and management regimes include watering the host plant to improve its vigor, and removing infested vegetation. Pruning infested branches is not generally effective because the haustoria can infiltrate deeply. Plucking the mistletoe herbage is a temporary treatment because it easily resprouts, but keeping its herbage sparse can help to reduce its seed production.

Wildlife & human uses

''Phoradendron'' species are larval host plants for a number of

Lepidoptera Lepidoptera ( ) or lepidopterans is an order (biology), order of winged insects which includes butterflies and moths. About 180,000 species of the Lepidoptera have been described, representing 10% of the total described species of living organ ...

. The buckthorn duskywing (''Erynnis pacuvius'') feeds on ''Phoradendron californicum''. ''Phoradendron'' are the preferred food of the Phainopepla, a silky-flycatcher. The male defends territories where fruiting mistletoe is abundant. There may actually be some mutualistic interactions between the parasite and the host in some ''Phoradendron'' species. The presence of ''Phoradendron juniperinum'' on host ''Juniperus'' ''monosperma,'' for example, has been suggested to increase dispersal of the host's seeds by birds. The mistletoe berries may attract frugivorous birds (e.g. thrushes) to eat the host juniper's seeds and disperse them. The net benefit on the hosts is difficult to quantify, however. The birds dispersing the host's seeds and benefiting the host, while at the same time dispersing the mistletoe's seeds and spreading the ''Phoradendron'' infection. '' Phoradendron californicum'' was used by Native American peoples as a food and medicinal remedy. Some ''Phoradendron'' species, such as '' Phoradendron serotinum'' and '' Phoradendron flavescens'', are used in North America as Christmas decoration, substituting for the European mistletoe '' Viscum album''. They are harvested commercially for that purpose.

Etymology

Nuttall named the genus ''Phoradendron'' from the Greek, ''phor'' (a thief) and ''dendron'' (tree), alluding to the genus' parasitic habit.

Taxonomy

There are roughly 235 to 240''Phoradendron''.
The Jepson Manual eFlora 2012. species in the genus. Species include: *'' Phoradendron aequatoris'' Urb. *'' Phoradendron anceps'' (Spreng.) G.Maza – goldenfruit mistletoe *'' Phoradendron argentinum'' *'' Phoradendron barahonae'' Urb. & Trel. – island mistletoe *'' Phoradendron bolleanum'' (Seem.) Eichl. – Bollean mistletoe *'' Phoradendron californicum'' Nutt. – desert mistletoe, mesquite mistletoe *'' Phoradendron canzacotoi'' Trel. *'' Phoradendron capitellatum'' Torr. ex Trel. – downy mistletoe or hairy mistletoe *'' Phoradendron coryae'' Trel. – oak mistletoe *'' Phoradendron crassifolium'' *'' Phoradendron densum'' Torr. ex Trel. – dense mistletoe *'' Phoradendron dichotomum'' (Bertero) Krug & Urb. – Bertero's mistletoe *'' Phoradendron emarginatum'' *'' Phoradendron flavescens'' same as ''Phoradendron leucarpum'' *'' Phoradendron hawksworthii'' (DC.) Griseb. – Hawksworth's mistletoe *'' Phoradendron hexastichum'' (DC.) Griseb. – tropical mistletoe *'' Phoradendron hieronymi'' *'' Phoradendron juniperinum'' A.Gray – juniper mistletoe *'' Phoradendron leucarpum'' (Raf.) Reveal & M.C.Johnst. (syn. ''P. flavescens'', ''P. serotinum'', ''P. tomentosum'') – oak mistletoe, eastern mistletoe; grows in the west as also in a line down the east from

New Jersey New Jersey is a U.S. state, state located in both the Mid-Atlantic States, Mid-Atlantic and Northeastern United States, Northeastern regions of the United States. Located at the geographic hub of the urban area, heavily urbanized Northeas ...

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

. *'' Phoradendron libocedri'' (Engelm.) Howell – incense-cedar mistletoe *'' Phoradendron liga'' *'' Phoradendron macrophyllum'' (Engelm.) Cockerell – Colorado Desert mistletoe or big-leaf mistletoe *'' Phoradendron madisonii'' Kuijt *'' Phoradendron mathiasenii''Wiens, D. and C. L. Calvin. (2011)
Two epiparasitic species of ''Phoradendron'' (Viscaceae) from Honduras: one new and for the other a range extension and host determination.
''Aliso'' 29(2) 119-23. *'' Phoradendron mucronatum'' (DC.) Krug & Urban – needletip mistletoe *'' Phoradendron nickrentianum'' Kuijt *'' Phoradendron olae''Kuijt, J. (1997)
''Phoradendron olae'' Kuijt, a new species from Mexico pivotal in the taxonomy of the genus, with comments on ''P. californicum'' Nutt.
''Brittonia'' 49(2), 181-88. *'' Phoradendron pauciflorum'' Torr. – fir mistletoe *'' Phoradendron piperoides'' (Kunth) Trel. – Piper mistletoe *'' Phoradendron pomasquianum'' Trel. *'' Phoradendron quadrangulare'' (Kunth) Griseb. *'' Phoradendron racemosum'' (Aubl.) Krug & Urb. – bigleaf mistletoe *'' Phoradendron rubrum'' (L.) Griseb. – mahogany mistletoe *'' Phoradendron serotinum'' same as ''Phoradendron leucarpum''. *'' Phoradendron tetrapterum'' Krug & Urb. – fourpart mistletoe *'' Phoradendron tomentosum'' (Lam.) Griseb. – leafy mistletoe; see ''Phoradendron leucarpum'' *'' Phoradendron trinervium'' (Lam.) Griseb. – angled mistletoe *'' Phoradendron tucumanense'' *'' Phoradendron villosum'' (Nutt.) Nutt. – Pacific mistletoe *'' Phoradendron wiensii'' Kuijt

References

External links

Mistletoes on Hardwoods in the United States.
USDA Forest Service. {{Authority control Parasitic plants Santalaceae genera