Editing Argyroxiphium

{{Short description|Genus of plants}}
{{Automatic taxobox
|image = Argyroxiphium_sandwicense_Haleakala.jpg
|image_caption = [[Haleakalā silversword]]
|display_parents = 3
|taxon = Argyroxiphium
|authority = [[Augustin Pyramus de Candolle|DC.]]
|synonyms_ref = <ref name=c>[https://archive.today/20141107194829/http://dixon.iplantcollaborative.org/CompositaeWeb/default.aspx?Page=NameDetails&TabNum=0&NameId=150854c4-9c16-4321-bfee-e5bd45137169 Flann, C (ed) 2009+ Global Compositae Checklist ]</ref>
|synonyms = ''Argyrophyton'' <small>Hook.</small>
}}

'''''Argyroxiphium''''' is a small genus of plants in the family [[Asteraceae]].<ref>[https://www.biodiversitylibrary.org/page/152103#page/673/mode/1up Candolle, Augustin Pyramus de. 1836. Prodromus Systematis Naturalis Regni Vegetabilis 5: 668]</ref><ref>[http://www.tropicos.org/Name/40019311 Tropicos, ''Argyroxiphium'' DC.]</ref> Its members are known by the common names '''silversword''' or '''greensword''' due to their long, narrow leaves and the silvery hairs on some species. The silverswords belong to a larger [[Adaptive radiation|radiation]] of over 50 species, including the physically different genera ''[[Dubautia]]'' and ''[[Wilkesia]]''. This grouping is often referred to as the [[silversword alliance]].<ref name="B. Baldwin 1998">[B. Baldwin. Age and Rate of Diversification of the Hawaiian Silversword Alliance (Compositae). 1998.]</ref> Botanist [[Peter H. Raven|P. H. Raven]] referred to this radiation as "the best example of adaptive radiation in plants".<ref>[Raven, P. H. Biology of Plants. 1990]</ref>

== Description ==

Species in ''Argyroxiphium'' are [[Perennial plant|perennial]], [[Rosette (botany)|rosette]]-forming [[shrub]]s. They may consist of a single large rosette or a collection of several rosettes.<ref name=":1">{{Cite journal |last1=Robichaux |first1=Robert H. |last2=Carr |first2=Gerald D. |last3=Liebman |first3=Matt |last4=Pearcy |first4=Robert W. |date=1990 |title=Adaptive Radiation of the Hawaiian Silversword Alliance (Compositae- Madiinae): Ecological, Morphological, and Physiological Diversity |url=https://www.jstor.org/stable/2399626 |journal=Annals of the Missouri Botanical Garden |volume=77 |issue=1 |pages=64–72 |doi=10.2307/2399626 |jstor=2399626 |issn=0026-6493}}</ref> In all ''Argyroxiphium'' species, long, narrow leaves contain interstitial gels hypothesized to function as water storage. For some species, leaves are covered with [[trichome]]s that provide protection from frost and create the plants' signature silver sheen.<ref>[S. Carlquist. Anatomy of Tropical Alpine Plants. 1994.]</ref>

A silversword rosette grows for at least five years before flowering, though some species grow for up to 90 years before initiating the [[Bolting (horticulture)|bolting]] process.<ref name=":2">{{Cite journal|last1=Krushelnycky|first1=Paul D.|last2=Loope|first2=Lloyd L.|last3=Giambelluca|first3=Thomas W.|last4=Starr|first4=Forest|last5=Starr|first5=Kim|last6=Drake|first6=Donald R.|last7=Taylor|first7=Andrew D.|last8=Robichaux|first8=Robert H.|date=2013|title=Climate-associated population declines reverse recovery and threaten future of an iconic high-elevation plant|url=https://onlinelibrary.wiley.com/doi/10.1111/gcb.12111|journal=Global Change Biology|language=en|volume=19|issue=3|pages=911–922|doi=10.1111/gcb.12111|pmid=23504847 |bibcode=2013GCBio..19..911K |s2cid=33617236 |url-access=subscription}}</ref> For [[monocarpic]] individuals with a single rosette, this ends in the death of the plant, though some individuals are [[polycarpic]]. The flowering stalks may be up to {{convert|1.5|m|ft|abbr=off}} tall, and are composed of up to 600 [[Capitulum (flower)|capitulae]].<ref name=":0">{{Cite journal |last1=Robichaux |first1=Robert H. |last2=Moriyasu |first2=Patrice Y. |last3=Enoka |first3=Jaime H. |last4=McDaniel |first4=Sierra |last5=Loh |first5=Rhonda K. |last6=Bio |first6=Kealiʻi F. |last7=Bakutis |first7=Ane |last8=Tunison |first8=J. Timothy |last9=Bergfeld |first9=Steven T. |last10=Perry |first10=J. Lyman |last11=Warshauer |first11=Frederick R. |date=2017-09-01 |title=Silversword and lobeliad reintroduction linked to landscape restoration on Mauna Loa and Kīlauea, and its implications for plant adaptive radiation in Hawaiʻi |url=https://www.sciencedirect.com/science/article/pii/S0006320717304706 |journal=Biological Conservation |language=en |volume=213 |pages=59–69 |doi=10.1016/j.biocon.2017.07.001 |bibcode=2017BCons.213...59R |issn=0006-3207}}</ref> These [[flower]] heads range in diameter from {{convert|1|cm|in|abbr=on}} to {{convert|6|cm|in|abbr=on}} and consist of a ring of [[Gynoecium|pistillate]] ray florets around 30 to 600 disk florets. The [[Corolla (flower)|corollae]] vary in color from wine red to yellow or white.<ref>{{Cite web |title=Hawaiian silversword alliance, UH Botany |url=http://www.botany.hawaii.edu/faculty/carr/flowers.htm |access-date=2022-03-02 |website=www.botany.hawaii.edu}}</ref> Because they are [[Self-incompatibility|self-incompatible]] and require [[Pollination#Mechanics|cross-pollination]] by [[Pollinator|insects]], many plants must flower at the same time in relatively close proximity to set [[seed]]. A significant population must exist for enough individuals to flower simultaneously and allow pollination to occur. The [[Achene|single-seeded fruits]] are usually dispersed by wind.<ref name=":0" />

Despite their different appearances, silverswords are very closely related to the genus ''[[Dubautia]]''. Sympatric species in ''Argyroxiphium'' and ''Dubautia'' often naturally produce fertile [[Hybrid (biology)|hybrids]] that run the gamut of morphological characteristics from the two genera. Together, ''Argyroxiphium'', ''Dubautia'', and ''Wilkesia'' make up the silversword alliance.<ref>{{Cite journal |last1=Baldwin |first1=Bruce G. |last2=Wood |first2=Kenneth R. |last3=Freyman |first3=William A. |date=October 2021 |title=Directionally biased habitat shifts and biogeographically informative cytonuclear discordance in the Hawaiian silversword alliance (Compositae) |journal=American Journal of Botany |language=en |volume=108 |issue=10 |pages=2015–2037 |doi=10.1002/ajb2.1757 |pmid=34694624 |s2cid=239766898 |issn=0002-9122|doi-access=free }}</ref>

== Evolution ==

The evolutionary roots of ''Argyroxiphium'' are the tarweeds in subtribe [[Madieae|Madiinae]].<ref name=":3">{{Cite journal |last1=Landis |first1=Michael J. |last2=Freyman |first2=William A. |last3=Baldwin |first3=Bruce G. |date=2018-10-09 |title=Retracing the Hawaiian silversword radiation despite phylogenetic, biogeographic, and paleogeographic uncertainty |url=https://doi.org/10.1111/evo.13594 |journal=Evolution |volume=72 |issue=11 |pages=2343–2359 |doi=10.1111/evo.13594 |pmid=30198108 |s2cid=52178628 |issn=0014-3820}}</ref> DNA analysis has revealed that silverswords form a [[clade]] within the Californian tarweed lineage. The relation is also physically evident—silversword capitulae and the flowers of Californian tarweeds both include sticky bracts that provide adhesion to birds for [[seed dispersal]].<ref>{{Cite journal |last1=Baldwin |first1=Bruce G. |last2=Wagner |first2=Warren L. |date=June 2010 |title=Hawaiian angiosperm radiations of North American origin |journal=Annals of Botany |volume=105 |issue=6 |pages=849–879 |doi=10.1093/aob/mcq052 |issn=1095-8290 |pmc=2876002 |pmid=20382966}}</ref> It is hypothesized that an individual plant from the Californian tarweeds was spread first to Kaua{{okina}}i, then spread to the other islands and developed into the silversword alliance.<ref name=":3" />

== Distribution ==

Silverswords are [[Endemism|endemic]] to [[Hawaii|Hawai{{okina}}i]] and occur only on the islands of [[Maui]] and [[Hawaii (island)|Hawai{{okina}}i]]. They grow primarily over {{convert|1200|m|ft|abbr=on}} above sea level in [[Hawaiian tropical rainforests#Bogs|bogs]], [[Hawaiian tropical high shrublands|alpine shrublands]], or [[Hawaiian tropical rainforests#Wet forests|wet shrublands]].<ref name=":1" /> ''A. sandwichense'' is able to grow at high altitudes between {{convert|2125|m|ft|abbr=on}} and {{convert|3750|m|ft|abbr=on}} on cinder and [[lava]] with relatively little rainfall. The Haleakalā silversword (''A sandwicense'' ssp. ''macrocephalum'') is constrained to [[Haleakalā]] on Maui while the Mauna Kea silversword (''A. sandwicense'' ssp. ''sandwicense'') is specific to [[Mauna Kea]] on Hawai{{okina}}i.<ref name=":2" /><ref name=":4">{{Cite journal |last1=Walker |first1=Lawrence R. |last2=Powell |first2=Elizabeth Ann |date=1999-07-01 |title=Regeneration of the Mauna Kea silversword Argyroxiphium sandwicense (Asteraceae) in Hawaii |url=https://www.sciencedirect.com/science/article/pii/S0006320798001323 |journal=Biological Conservation |language=en |volume=89 |issue=1 |pages=61–70 |doi=10.1016/S0006-3207(98)00132-3 |bibcode=1999BCons..89...61W |issn=0006-3207|url-access=subscription }}</ref> Each of the other species is found primarily at lower altitudes with much higher annual rainfall.<ref name=":1" />

== Conservation ==

The Mauna Loa or Ka{{okina}}ū silversword (''A. kauense'') has been classified as [[Critically Endangered|critically endangered]] and the Mauna Kea and Halekalā silverswords (''A. sandwichense'') have been classified as [[Endangered species|endangered]] in the [[IUCN Red List]].<ref>{{Cite web |last=Bruegmann |first=M. M. |last2=Caraway |first2=V. |date=2003 |title=Argyroxiphium kauense |url=https://www.iucnredlist.org/species/44113/10858069 |access-date=July 6, 2024 |website=The IUCN Red List of Threatened Species}}</ref><ref>{{Cite web |last=Caraway |first=V. |last2=Keir |first2=M. |date=2020 |title=Silversword Argyroxiphium sandwicense |url=https://www.iucnredlist.org/species/44157/78765991 |access-date=July 6, 2024 |website=The IUCN Red List of Threatened Species}}</ref> Direct damage from humans and from [[ungulate]] browsing have significantly damaged silversword populations, but dedicated management efforts have resulted in successful conservation of some species. In particular, the Haleakalā silversword population reached a low of approximately 4,000 plants in the 1920s, but rebounded to over 6,500 individuals by 1970.<ref name=":2" /> On the other hand, the Mauna Kea silversword population was composed of approximately 50 naturally occurring individuals and 500 outplanted individuals in 1999.<ref name=":4" /> The East Maui greensword (''A. virescens'') is apparently [[Holocene extinction|extinct]], but in 1989 plants were discovered that appear to be [[Hybrid (biology)#Hybrid plants|hybrids]] between it and the [[Haleakala silversword|Haleakalā silversword]]. The hybrid is known as the [[Pu'u 'Alaea greensword]].<ref>{{cite web |first=Gerald |last=Carr |url=http://www.botany.hawaii.edu/faculty/carr/avir.htm |title=''Argyroxiphium virescens'' Hillebrand |work=Hawaiian Silversword Alliance |publisher=University of Hawaii |date=1997-03-20 |accessdate=2009-11-01| archiveurl= https://web.archive.org/web/20090918105345/http://www.botany.hawaii.edu/faculty/carr/avir.htm| archivedate= 18 September 2009 | url-status= live}}</ref>

== Species ==

;Accepted species<ref name=c/>
* ''[[Argyroxiphium caliginis]]'' <small>[[Charles Noyes Forbes|C.N.Forbes]]</small> – {{okina}}Eke silversword
* ''[[Argyroxiphium grayanum]]'' <small>([[William Hillebrand|Hillebr.]]) [[Otto Degener|O. Deg.]]</small> – greensword
* ''[[Argyroxiphium × kai]]'' <small>D.D.Keck</small> ''(A. caliginis × A. grayanum)''
* ''[[Argyroxiphium kauense]]'' <small>([[Joseph Rock|Rock]] & M.Neal) [[Otto Degener|O.Deg.]] & I.Deg.</small> – Mauna Loa or Ka{{okina}}ū silversword
* ''[[Argyroxiphium sandwicense]]'' <small>[[Augustin Pyrame de Candolle|DC.]]</small> – silversword
** ''Argyroxiphium sandwicense'' subsp. ''sandwicense'' <small>DC.</small> – [[Mauna Kea silversword]]
** ''Argyroxiphium sandwicense'' subsp. ''macrocephalum'' <small>([[Asa Gray|A.Gray]]) Meyrat</small> – [[Haleakalā silversword]]
* ''[[Argyroxiphium virescens]]'' <small>Hillebr.</small> – East Maui greensword ([[Holocene extinction|extinct]])

;Formerly included<ref name=c/>
now in ''[[Wilkesia]]''
* ''A. gymnoxiphium – [[Wilkesia gymnoxiphium]]''

== Gallery ==
<gallery>
File:Starr 980630-1521 Argyroxiphium grayanum.jpg|Greensword
File:Argyroxiphium grayanum Puu Kukui.jpg|Greensword, [[Puu Kukui|Pu{{okina}}u Kukui]] bog
File:Silversword Haleakala.jpg|Haleakalā silversword
File:Haleakala silversword.jpg|Silversword in Haleakalā Crater
File:Dubautia silversword hybrid.jpg|[[Argyroxiphium sandwicense subsp. macrocephalum x Dubautia menziesii|''Dubautia''-silversword]] hybrid in Haleakalā Crater
File:Starr 011205-0093 Argyroxiphium sandwicense subsp. sandwicense.jpg|Mauna Kea silversword
File:Mauna Kea silversword2.jpg|Mauna Kea silversword
File:Mauna Kea silversword3.jpg|Mauna Kea silversword flowering
File:MaunaKeaSilversword.JPG|Mauna Kea silversword
File:Kahuku silversword habitat.jpg|Mauna Loa silversword habitat, Kahuku
File:Kahuku silversword1.jpg|Mauna Loa silversword, multiple rosettes
File:Kahuku silversword2.jpg|Mauna Loa silversword, single rosette
File:Silversword (Healakala) close up.jpg|Haleakalā silversword (close-up)
File:Mauna Loa silversword flowering.jpg|Mauna Loa silversword flowering
</gallery>

==References==
{{Reflist}}

==External links==
* {{Commons category-inline|Argyroxiphium}}
* {{Wikispecies-inline}}
* [https://archive.today/20130103222026/http://www.kaahelehawaii.com/pages/nathist_endangered_species.htm Kaʻahele Hawaiʻi Native Plants]
* [http://www.botany.hawaii.edu/faculty/carr/asm.htm Hawaiian silversword alliance, University of Hawaii Botany]
* [http://plants.usda.gov/core/profile?symbol=argyr US Department of Agriculture plants profile]

{{Taxonbar|from=Q2414693}}

[[Category:Argyroxiphium| ]]
[[Category:Endemic flora of Hawaii]]
[[Category:Asteraceae genera]]