Arceuthobium
Encyclopedia
The genus
Arceuthobium, commonly called Dwarf Mistletoe
s, is a genus of 42 species of parasitic plant
s that parasitize members of Pinaceae
and Cupressaceae
in North America
, Central America
, Asia
and Africa
. Of the 42 species, 39 and 21 are endemic to North America and the United States, respectively. They all have very reduced shoots and leaves
(mostly reduced to scales) with the bulk of the plant living under the host's bark. Recently the number of species within the genus has been reduced to 26 as a result of more detailed genetic analysis.
In western forest ecosystems of North America
, numerous dwarf mistletoe species are considered to be serious forest-borne disease agents. Severe dwarf mistletoe infection can result in a reduction in tree growth, premature tree mortality, reduced seed and cone development, reduced wood quality, and increase the susceptibility of the host tree to pathogen and/or insect attack. Most of the commercially important conifers in western North America are parasitized by one or more dwarf mistletoes.
The interaction between dwarf mistletoes and their host can be generalized as a source-to-sink relationship. Dwarf mistletoes derive the majority of their nutrition from the host’s vascular tissue
s. Dwarf mistletoes have a root-like endophytic
system, composed of primary and secondary haustoria
, which invade, but do not injure, both the xylem
and phloem
of the host. Because this root-like endophytic system is not soil
-borne, dwarf mistletoes are solely dependent on their host for water. Along a xylem-to-xylem link, dwarf mistletoes draw water from their host due to differences in water potential between dwarf mistletoes and their hosts. Dwarf mistletoes facilitate this water gradient by having greater transpiration rates, thereby producing lower water potentials and allowing water to flow from the hosts to the dwarf mistletoes. The water gradient or transpiration
stream is consistently maintained, even when the host is under moderate water deficits.
In addition to host-water dependence, dwarf mistletoes must acquire carbohydrate
and mineral nutrition from their hosts. Dwarf mistletoes have both chlorophyll
a and chlorophyll b and the necessary mechanisms for photosynthesis, but chlorophyll concentrations in dwarf mistletoes are approximately 1/5 to 1/10 of those found in their host’s foliage, and dwarf mistletoes have low photosynthetic rates as measured by the rate of carbon fixation
. The principal carbohydrate transported from the host to dwarf mistletoe is sucrose
. Dwarf mistletoes are phloem deficient; therefore, dwarf mistletoes draw carbohydrates from their hosts by connections to the host phloem and ray parenchyma
. The rate of carbohydrate transport between dwarf mistletoes varies according to season, but dwarf mistletoes continuously draw carbohydrates from their hosts throughout the year.
They are dioecious
, individual plants being either male or female. The fruit
is unusual in that it builds up hydrostatic pressure internally when ripe and shoots the single sticky seed
up to speeds nearly 50 miles per hour (80.5 km/h), an example of rapid plant movement
. The seeds are enveloped in a hygroscopic
, glue-like substance called viscin. Many fail to land on a suitable host's shoot, but just as many succeed, and in this way they are spread through the forests as a pest front. The spread of dwarf mistletoes in forest stands is greatest from the overstory to the understory (gravity). Advantageous stand conditions for the spread of dwarf mistletoes include an uneven-aged stand structure with severely infected-hosts in dominant and codominant crown classes, species composition dominated by the primary host, and tree densities that are between 175 - 500 trees/ha.
There are also a number of species from Europe
and Asia
including one of the smallest in the genus, A. minutissimum that lives on its host, Pinus wallichiana
in the Himalaya.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Arceuthobium, commonly called Dwarf Mistletoe
Mistletoe
Mistletoe is the common name for obligate hemi-parasitic plants in several families in the order Santalales. The plants in question grow attached to and within the branches of a tree or shrub.-Mistletoe in the genus Viscum:...
s, is a genus of 42 species of parasitic plant
Parasitic plant
A parasitic plant is one that derives some or all of its sustenance from another plant. About 4,100 species in approximately 19 families of flowering plants are known. Parasitic plants have a modified root, the haustorium, that penetrates the host plant and connects to the xylem, phloem, or...
s that parasitize members of Pinaceae
Pinaceae
Pinaceae are trees or shrubs, including many of the well-known conifers of commercial importance such as cedars, firs, hemlocks, larches, pines and spruces. The family is included in the order Pinales, formerly known as Coniferales. Pinaceae are supported as monophyletic by its protein-type sieve...
and Cupressaceae
Cupressaceae
The Cupressaceae or cypress family is a conifer family with worldwide distribution. The family includes 27 to 30 genera , which include the junipers and redwoods, with about 130-140 species in total. They are monoecious, subdioecious or dioecious trees and shrubs from 1-116 m tall...
in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, Central America
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
, Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
and Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
. Of the 42 species, 39 and 21 are endemic to North America and the United States, respectively. They all have very reduced shoots and leaves
Leaves
-History:Vocalist Arnar Gudjonsson was formerly the guitarist with Mower, and he was joined by Hallur Hallsson , Arnar Ólafsson , Bjarni Grímsson , and Andri Ásgrímsson . Late in 2001 they played with Emiliana Torrini and drew early praise from the New York Times...
(mostly reduced to scales) with the bulk of the plant living under the host's bark. Recently the number of species within the genus has been reduced to 26 as a result of more detailed genetic analysis.
In western forest ecosystems of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, numerous dwarf mistletoe species are considered to be serious forest-borne disease agents. Severe dwarf mistletoe infection can result in a reduction in tree growth, premature tree mortality, reduced seed and cone development, reduced wood quality, and increase the susceptibility of the host tree to pathogen and/or insect attack. Most of the commercially important conifers in western North America are parasitized by one or more dwarf mistletoes.
The interaction between dwarf mistletoes and their host can be generalized as a source-to-sink relationship. Dwarf mistletoes derive the majority of their nutrition from the host’s vascular tissue
Vascular tissue
Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue:...
s. Dwarf mistletoes have a root-like endophytic
Endophyte
An endophyte is an endosymbiont, often a bacterium or fungus, that lives within a plant for at least part of its life without causing apparent disease. Endophytes are ubiquitous and have been found in all the species of plants studied to date; however, most of these endophyte/plant relationships...
system, composed of primary and secondary haustoria
Haustorium
In botany, a haustorium is the appendage or portion of a parasitic fungus or of the root of a parasitic plant that penetrates the host's tissue and draws nutrients from it. Haustoria do not penetrate the host's cell membranes.Fungi in all major divisions form haustoria...
, which invade, but do not injure, both the xylem
Xylem
Xylem is one of the two types of transport tissue in vascular plants. . The word xylem is derived from the Classical Greek word ξυλον , meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant...
and phloem
Phloem
In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...
of the host. Because this root-like endophytic system is not soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
-borne, dwarf mistletoes are solely dependent on their host for water. Along a xylem-to-xylem link, dwarf mistletoes draw water from their host due to differences in water potential between dwarf mistletoes and their hosts. Dwarf mistletoes facilitate this water gradient by having greater transpiration rates, thereby producing lower water potentials and allowing water to flow from the hosts to the dwarf mistletoes. The water gradient or transpiration
Transpiration
Transpiration is a process similar to evaporation. It is a part of the water cycle, and it is the loss of water vapor from parts of plants , especially in leaves but also in stems, flowers and roots. Leaf surfaces are dotted with openings which are collectively called stomata, and in most plants...
stream is consistently maintained, even when the host is under moderate water deficits.
In addition to host-water dependence, dwarf mistletoes must acquire carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
and mineral nutrition from their hosts. Dwarf mistletoes have both chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
a and chlorophyll b and the necessary mechanisms for photosynthesis, but chlorophyll concentrations in dwarf mistletoes are approximately 1/5 to 1/10 of those found in their host’s foliage, and dwarf mistletoes have low photosynthetic rates as measured by the rate of carbon fixation
Carbon fixation
In biology, carbon fixation is the reduction of carbon dioxide to organic compounds by living organisms. The obvious example is photosynthesis. Carbon fixation requires both a source of energy such as sunlight, and an electron donor such as water. All life depends on fixed carbon. Organisms that...
. The principal carbohydrate transported from the host to dwarf mistletoe is sucrose
Sucrose
Sucrose is the organic compound commonly known as table sugar and sometimes called saccharose. A white, odorless, crystalline powder with a sweet taste, it is best known for its role in human nutrition. The molecule is a disaccharide composed of glucose and fructose with the molecular formula...
. Dwarf mistletoes are phloem deficient; therefore, dwarf mistletoes draw carbohydrates from their hosts by connections to the host phloem and ray parenchyma
Parenchyma
Parenchyma is a term used to describe a bulk of a substance. It is used in different ways in animals and in plants.The term is New Latin, f. Greek παρέγχυμα - parenkhuma, "visceral flesh", f. παρεγχεῖν - parenkhein, "to pour in" f. para-, "beside" + en-, "in" + khein, "to pour"...
. The rate of carbohydrate transport between dwarf mistletoes varies according to season, but dwarf mistletoes continuously draw carbohydrates from their hosts throughout the year.
Plant sexuality
Plant sexuality covers the wide variety of sexual reproduction systems found across the plant kingdom. This article describes morphological aspects of sexual reproduction of plants....
, individual plants being either male or female. The fruit
Fruit
In broad terms, a fruit is a structure of a plant that contains its seeds.The term has different meanings dependent on context. In non-technical usage, such as food preparation, fruit normally means the fleshy seed-associated structures of certain plants that are sweet and edible in the raw state,...
is unusual in that it builds up hydrostatic pressure internally when ripe and shoots the single sticky seed
Seed
A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
up to speeds nearly 50 miles per hour (80.5 km/h), an example of rapid plant movement
Rapid plant movement
Rapid plant movement encompasses movement in plant structures occurring over a very short period of time, usually under one second. For example, the Venus Flytrap closes its trap in about 100 milliseconds. The Dogwood Bunchberry's flower opens its petals and fires pollen in less than 0.5 milliseconds...
. The seeds are enveloped in a hygroscopic
Hygroscopy
Hygroscopy is the ability of a substance to attract and hold water molecules from the surrounding environment. This is achieved through either absorption or adsorption with the absorbing or adsorbing material becoming physically 'changed,' somewhat, by an increase in volume, stickiness, or other...
, glue-like substance called viscin. Many fail to land on a suitable host's shoot, but just as many succeed, and in this way they are spread through the forests as a pest front. The spread of dwarf mistletoes in forest stands is greatest from the overstory to the understory (gravity). Advantageous stand conditions for the spread of dwarf mistletoes include an uneven-aged stand structure with severely infected-hosts in dominant and codominant crown classes, species composition dominated by the primary host, and tree densities that are between 175 - 500 trees/ha.
There are also a number of species from Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
and Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
including one of the smallest in the genus, A. minutissimum that lives on its host, Pinus wallichiana
Blue Pine
Pinus wallichiana is a pine native to the Himalaya, Karakoram and Hindu Kush mountains, from eastern Afghanistan east across northern Pakistan and India to Yunnan in southwest China. It grows at high altitudes in mountain valleys at altitudes of 1800–4300 m , and is a tree from 30–50 m in height...
in the Himalaya.
Species
- Arceuthobium abietinumArceuthobium abietinumArceuthobium abietinum is a species of dwarf mistletoe known as fir dwarf mistletoe. It is native to western North America from Washington to New Mexico to northern Mexico, where it lives in coniferous forests as a parasite on various species of fir, particularly white fir, giant fir, and red fir...
Engelm. ex Munz - Arceuthobium americanumArceuthobium americanumArceuthobium americanum is a species of dwarf mistletoe known as American dwarf mistletoe and lodgepole-pine dwarf mistletoe. It is a common plant of western North America where it lives in high elevation pine forests. It is a parasitic plant which lives upon the Lodgepole Pine, particularly the...
Nutt. ex Engelm. - Arceuthobium apachecum Hawksworth & Wiens
- Arceuthobium blumeri A. Nels.
- Arceuthobium californicum Hawksworth & Wiens
- Arceuthobium campylopodumArceuthobium campylopodumArceuthobium campylopodum is a species of dwarf mistletoe known as western dwarf mistletoe. It is native to the low to moderate elevation coniferous forests of western North America. It is a common parasite of several species of pine tree, including Jeffrey Pine, Ponderosa Pine, and Coulter Pine...
Engelm. - Arceuthobium cyanocarpum (A. Nels. ex Rydb.) A. Nels.
- Arceuthobium divaricatumArceuthobium divaricatumArceuthobium divaricatum is a species of dwarf mistletoe known as pinyon dwarf mistletoe. It is native to the southwestern United States and Baja California, where it lives in woodlands as a parasite on various species of pine, particularly Colorado Pinyon and Single-leaf Pinyon...
Engelm. - Arceuthobium douglasiiArceuthobium douglasiiArceuthobium douglasii is a species of dwarf mistletoe known as Douglas-fir dwarf mistletoe. It is native to western North America from British Columbia to Texas to California, where it lives in forest and woodland as a parasite on Douglas-fir trees. This is a greenish shrub which is visible as a...
Engelm. - Arceuthobium gillii Hawksworth & Wiens
- Arceuthobium globosum Hawksw. & Wiens
- Arceuthobium laricis (Piper) St. John
- Arceuthobium littorumArceuthobium littorumArceuthobium littorum is a species of dwarf mistletoe known as coastal dwarf mistletoe. It is endemic to the coastline of northern California, where it lives as a parasite on Bishop Pine and Monterey Pine trees. This is a dark brown or greenish shrub which is visible as a network of scaly stems...
Hawksworth, Wiens & Nickrent - Arceuthobium microcarpum (Engelm.) Hawksworth & Wiens
- Arceuthobium minutissimum
- Arceuthobium monticolaArceuthobium monticolaArceuthobium monticola is a species of dwarf mistletoe known as western white pine dwarf mistletoe. It is endemic to the Klamath Mountains of northern California and southern Oregon, where it lives as a parasite on Western White Pine trees. This is a brownish to reddish shrub which is visible as a...
Hawksworth, Wiens & Nickrent - Arceuthobium occidentale Engelm.
- Arceuthobium oxycedri
- Arceuthobium pusillum Peck
- Arceuthobium siskiyouenseArceuthobium siskiyouenseArceuthobium siskiyouense is a species of dwarf mistletoe known as knobcone pine dwarf mistletoe. It is endemic to the Klamath Mountains of northern California and southern Oregon, where it lives as a parasite on Knobcone Pine trees. This is a brownish shrub which is visible as a network of scaly...
Hawksworth, Wiens & Nickrent - Arceuthobium tsugense (Rosendahl) G.N. Jones
- Arceuthobium vaginatum (Humb. & Bonpl. ex Willd.) J. Presl (Syn. Viscum vaginatum Humb. & Bonpl. ex Willd.)