Arceuthobium
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2008-06-24T14:49:32Z
Thijs!bot
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robot Adding: [[pt:Arceuthobium]]
{{Taxobox
| name = Dwarf Mistletoes
| image = Arceuthobium oxycedri.jpg
| image_size = 225px
| image_caption = ''Arceuthobium oxycedri''
| regnum = [[Plant]]ae
| divisio = [[Magnoliophyta]]
| classis = [[Magnoliopsida]]
| ordo = [[Santalales]]
| familia = [[Santalaceae]]
| genus = '''''Arceuthobium'''''
| genus_authority = [[Friedrich August Marschall von Bieberstein|M.Bieb.]]
| subdivision_ranks = Species
| subdivision =
See [[list_of_Arceuthobium_species|list of ''Arceuthobium'' species]]
}}
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<ref name="Nick">{{cite journal | last = Nickrent | first = D.L. | coauthors = M.A. García, M.P. Martín, R.L. Mathiasen | year = 2004 | title = A phylogeny of all species of ''Arceuthobium'' (Viscaceae) using nuclear and chloroplast DNA sequences | journal = American Journal of Botany | volume = 91 | pages = 125–138 | doi = 10.3732/ajb.91.1.125}}</ref>.
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 tissues. 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 dioxide 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.
[[Image:Arceuthobium_vaginatum_subsp._cryptopodum.jpg|thumb|left|Female plant of ''A. vaginatum'' susbp. ''cryptopodum'' on Ponderosa pine.]]
They are [[plant sexuality|dioecious]], individual plants being either male or female. The [[fruit]]s that follow [[fertilization]] are unusual in building hydrostatic pressure internally when ripe and shooting the single sticky [[seed]] up to nearly 50mph, 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, ''[[Blue Pine|Pinus wallichiana]]'' in the [[Himalaya]].
== Species ==
* ''[[Arceuthobium abietinum]]'' <span class="Person">Engelm. ex Munz</span>
* ''[[Arceuthobium americanum]]'' <span class="Person">Nutt. ex Engelm.</span>
* ''[[Arceuthobium apachecum]]'' <span class="Person">Hawksworth & Wiens</span>
* ''[[Arceuthobium blumeri]]'' <span class="Person">A. Nels.</span>
* ''[[Arceuthobium californicum]]'' <span class="Person">Hawksworth & Wiens</span>
* ''[[Arceuthobium campylopodum]]'' <span class="Person">Engelm.</span>
* ''[[Arceuthobium cyanocarpum]]'' <span class="Person">(A. Nels. ex Rydb.) A. Nels.</span>
* ''[[Arceuthobium divaricatum]]'' <span class="Person">Engelm.</span>
* ''[[Arceuthobium douglasii]]'' <span class="Person">Engelm.</span>
* ''[[Arceuthobium gillii]]'' <span class="Person">Hawksworth & Wiens</span>
* ''[[Arceuthobium globosum]]'' <span class="Person">Hawksw. & Wiens</span>
* ''[[Arceuthobium laricis]]'' <span class="Person">(Piper) St. John</span>
* ''[[Arceuthobium littorum]]'' <span class="Person">Hawksworth, Wiens & Nickrent</span>
* ''[[Arceuthobium microcarpum]]'' <span class="Person">(Engelm.) Hawksworth & Wiens</span>
* ''[[Arceuthobium minutissimum]]''
* ''[[Arceuthobium monticola]]'' <span class="Person">Hawksworth, Wiens & Nickrent</span>
* ''[[Arceuthobium occidentale]]'' <span class="Person">Engelm.</span>
* ''[[Arceuthobium oxycedri]]''
* ''[[Arceuthobium pusillum]]'' <span class="Person">Peck</span>
* ''[[Arceuthobium siskiyouense]]'' <span class="Person">Hawksworth, Wiens & Nickrent</span>
* ''[[Arceuthobium tsugense]]'' <span class="Person">(Rosendahl) G.N. Jones</span>
* ''[[Arceuthobium vaginatum]]'' <span class="Person">(Humb. & Bonpl. ex Willd.) J. Presl</span> (Syn. ''Viscum vaginatum'' <span class="Person">Humb. & Bonpl. ex Willd.</span>)
==References and external links==
{{reflist}}
* Hawksworth, F. G., & Wiens, D. (1996). ''Dwarf Mistletoes: Biology, Pathology, and Systematics''. USDA Forest Service, Agriculture Handbook 709.
* Kenaley, S.C., R.L. Mathiasen, & C.M. Daugherty. 2006. Selection of dwarf mistletoe-infected ponderosa pines by ''Ips'' species (Coleoptera: Scolytidae) in northern Arizona. WNAN 66:279-284.
*Mathiasen, R.L. 1996. Dwarf mistletoes in forest canopies. Northwest. Sci. 70:61-71.
* [http://www.parasiticplants.siu.edu/Viscaceae/images/CAM.male.JPEG Maleshoots of ''A. campylopodum'' in California]
* [http://www.parasiticplants.siu.edu/Viscaceae/images/TSU.shorepine.JPEG Fruiting plant of ''A. campylopodum'' on Pine shoot]
* [http://plants.usda.gov/java/profile?symbol=ARCEU PLANTS profile for Arceuthobium (United States) including range maps.]
[[Category:Santalales]][[Category:Parasitic_plants]][[Category:Epiphytes]]
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