Argyroxiphium

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Argyroxiphium
Argyroxiphium sandwicense Haleakala.jpg
Haleakalā silversword
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Asterales
Family: Asteraceae
Subfamily: Asteroideae
Tribe: Madieae
Subtribe: Madiinae
Genus: Argyroxiphium
DC.
Synonyms [1]

ArgyrophytonHook.

Argyroxiphium is a small genus of plants in the family Asteraceae. [2] [3] 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 radiation of over 50 species, including the physically different genera Dubautia and Wilkesia . This grouping is often referred to as the silversword alliance. [4] Botanist P. H. Raven referred to this radiation as "the best example of adaptive radiation in plants". [5]

Contents

Description

Species in Argyroxiphium are perennial, rosette-forming shrubs. They may consist of a single large rosette or a collection of several rosettes. [6] In all Argyroxiphium species, long, narrow leaves contain interstitial gels hypothesized to function as water storage. For some species, leaves are covered with trichomes that provide protection from frost and create the plants' signature silver sheen. [7]

A silversword rosette grows for at least five years before flowering, though some species grow for up to 90 years before initiating the bolting process. [8] 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 1.5 metres (4.9 feet) tall, and are composed of up to 600 capitulae. [9] These flower heads range in diameter from 1 cm (0.39 in) to 6 cm (2.4 in) and consist of a ring of pistillate ray florets around 30 to 600 disk florets. The corollae vary in color from wine red to yellow or white. [10] Because they are self-incompatible and require cross-pollination by 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 single-seeded fruits are usually dispersed by wind. [9]

Despite their different appearances, silverswords are very closely related to the genus Dubautia . Sympatric species in Argyroxiphium and Dubautia often naturally produce fertile hybrids that run the gamut of morphological characteristics from the two genera. Together, Argyroxiphium, Dubautia, and Wilkesia make up the silversword alliance. [11]

Evolution

The evolutionary roots of Argyroxiphium are the tarweeds in subtribe Madiinae. [12] 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. [13] It is hypothesized that an individual plant from the Californian tarweeds was spread first to Kauaʻi, then spread to the other islands and developed into the silversword alliance. [12]

Distribution

Silverswords are endemic to Hawaiʻi and occur only on the islands of Maui and Hawaiʻi. They grow primarily over 1,200 m (3,900 ft) above sea level in bogs, alpine shrublands, or wet shrublands. [6] A. sandwichense is able to grow at high altitudes between 2,125 m (6,972 ft) and 3,750 m (12,300 ft) 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 Hawaiʻi. [8] [14] Each of the other species is found primarily at lower altitudes with much higher annual rainfall. [6]

Conservation

The Mauna Loa or Kaʻū silversword (A. kauense) has been classified as critically endangered and the Mauna Kea and Halekalā silverswords (A. sandwichense) have been classified as endangered in the IUCN Red List. [15] [16] 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. [8] On the other hand, the Mauna Kea silversword population was composed of approximately 50 naturally occurring individuals and 500 outplanted individuals in 1999. [14] The East Maui greensword (A. virescens) is apparently extinct, but in 1989 plants were discovered that appear to be hybrids between it and the Haleakalā silversword. The hybrid is known as the Pu'u 'Alaea greensword. [17]

Species

Accepted species [1]
Formerly included [1]

now in Wilkesia

Related Research Articles

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Located about 2,300 miles (3,680 km) from the nearest continental shore, the Hawaiian Islands are the most isolated group of islands on the planet. The plant and animal life of the Hawaiian archipelago is the result of early, very infrequent colonizations of arriving species and the slow evolution of those species—in isolation from the rest of the world's flora and fauna—over a period of at least 5 million years. As a consequence, Hawai'i is home to a large number of endemic species. The radiation of species described by Charles Darwin in the Galapagos Islands which was critical to the formulation of his theory of evolution is far exceeded in the more isolated Hawaiian Islands.

<span class="mw-page-title-main">Haleakalā National Park</span> National park in Hawaii

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<i>Argyroxiphium sandwicense <span style="font-style:normal;">subsp.</span> macrocephalum</i> Subspecies of flowering plant

Argyroxiphium sandwicense subsp. macrocephalum, the east Maui silversword or Haleakala silversword, is a rare plant, part of the family Asteraceae. The silversword in general is referred to as ʻāhinahina in Hawaiian.

<span class="mw-page-title-main">Silversword alliance</span> Group of Hawaiian plants that show remarkable diversity

The silversword alliance, also known as the tarweeds, refers to an adaptive radiation of around 30 species in the composite or sunflower family, Asteraceae. The group is endemic to Hawaii, and is derived from a single immigrant to the islands. For radiating from a common ancestor at an estimated 5.2±0.8 Ma, the clade is extremely diverse, composed of trees, shrubs, subshrubs, mat-plants, cushion plants, rosette plants, and lianas.

<i>Wilkesia gymnoxiphium</i> Species of plant

Wilkesia gymnoxiphium, is a species of flowering plant in the family Asteraceae that is endemic to the island of Kauaʻi in Hawaiʻi. It is classified as endangered on the IUCN Red List. Wilkesia is one of three genera, with Argyroxiphium and Dubautia that are believed to be descendant from a single species related to the North American tarweed. The members of these three genera constitute what is called the silversword alliance, a group whose exceedingly close genetic heritage is not reflected in their exceptionally diverse morphologies.

<i>Argyroxiphium sandwicense</i> Species of plant

Argyroxiphium sandwicense, the Hawaiʻi silversword, or hinahina is a species of silversword. It is endemic to Hawaii. The two subspecies are separated by geography. Both subspecies are rare, threatened and federally protected.

<i>Argyroxiphium kauense</i> Species of plant

The Mauna Loa silversword, Argyroxiphium kauense, or Kaʻū silversword, is a rare species of flowering plant in the aster family. It is endemic to the eastern and southern slopes of Mauna Loa on the island of Hawaiʻi. A. kauense occurs in mountainous shrublands, bogs, and open mesic forest. The species is managed by the National Park Service and Hawaiʻi State Department of Forestry and Wildlife. It is a federally listed endangered species of the United States. There are three known populations remaining, for a total of fewer than 1000 individuals.

Argyroxiphium virescens was a species of flowering plant in the family Asteraceae that was last seen in 1945. It was found only in the Hawaiian Islands where it was endemic to the eastern part of Maui. Its natural habitats were subtropical or tropical moist montane forests and subtropical or tropical high-altitude shrubland. It is officially declared extinct, but in 1989 plants were discovered that appear to be hybrids between it and the Haleakalā silversword. This hybrid is known as the Pu'u 'Alaea greensword.

<span class="mw-page-title-main">Hawaiian tropical high shrublands</span> Tropical savanna ecoregion of the Hawaiian Islands in the United States

The Hawaiian tropical high shrublands are a tropical savanna ecoregion in the Hawaiian Islands.

<span class="mw-page-title-main">Madieae</span> Tribe of flowering plants

Madieae is a tribe of flowering plants in the family Asteraceae. It is sometimes considered a subtribe of Heliantheae. Notable species include the tarweeds of the Western United States as well as the silverswords of Hawaii.

<i>Wilkesia</i> Genus of flowering plants

Wilkesia is a genus of Hawaiian plants in the tribe Madieae within the family Asteraceae. It contains two perennials, both of which are endemic to the island of Kauaʻi in Hawaiʻi. Wilkesia is a component of the silversword alliance and is named after Captain Charles Wilkes.

<i>Wilkesia hobdyi</i> Species of plant

Wilkesia hobdyi, the dwarf iliau, is a species of flowering plant in the family Asteraceae that is endemic to the island of Kauaʻi in Hawaii. It was first collected in 1968, and was not formally described until 1971. The number of living plants is estimated at fewer than 300. It is considered Critically Imperiled in global rank which means it is at very high risk of extinction. It has been a federally protected species since 1992. The genus Wilkesia is one of three genera constituting the silversword alliance, a group of highly diverse yet genetically exceedingly closely related species, all thought to be descended from a colonizing ancestor related to the tarweed of North America.

<i>Argyroxiphium grayanum</i> Species of plant

Argyroxiphium grayanum, commonly known as the greensword, is a species of flowering plant in the family Asteraceae, and a member of the silversword alliance, a group of over 50 species which are diverse in morphology and habitat but are genetically closely related.

<span class="mw-page-title-main">Mauna Kea silversword</span> Subspecies of flowering plant

Argyroxiphium sandwicense subsp. sandwicense, the Mauna Kea silversword, is a highly endangered flowering plant endemic to the island of Hawaiʻi of Hawaii. It is the "crown jewel" of the volcanic mountain Mauna Kea, from which it derives its English name. The Hawaiian name is ʻahinahina; it applies to silverswords more broadly. The Mauna Kea silversword was once common on the volcano, and extraordinary conservation efforts are being made to preserve the species.

Argyroxiphium virescens × sandwicense subsp. macrocephalum, commonly known as the Pu'u 'Alaea greensword is a hybrid species of silversword plant in the family Asteraceae, and is a part of the silversword alliance. It is a hybrid between two taxons of silversword plant in the genus Argyroxiphium, being the presumably extinct Argyroxiphium virescens, and a subspecies, Argyroxiphium sandwicense subsp. macrocephalum. The hybrid species was discovered in 1989, when an individual flowered, which revealed hybridization features of two species of silversword. It is endemic to East Maui, primarily near the town of Pu’u Alaea, where it is seen growing beside other Argyroxiphium species. The population of the hybrid species is unknown, but is likely under threat of feral goats, and pigs that plague silversword plants.

<i>Argyroxiphium sandwicense</i> subsp. <i>macrocephalum</i> x <i>Dubautia menziesii</i> Hybrid species of plant

Argyroxiphium sandwicense subsp. macrocephalum x Dubautia menziesii, commonly known as the Dubautia-silversword, is a hybrid species of silversword plant in the family Asteraceae, and is a part of the silversword alliance. The hybrid was formed between Argyroxiphium sandwicense subsp. macrocephalum and Dubautia menziesii, which are both species of plant native to the Haleakalā Shield Volcano, Maui, primarily in the Haleakalā Crater, that grow in alpine and subalpine zones.

<i>Dubautia scabra</i> Species of plant

Dubautia scabra, or rough dubautia, is a species of Dubautia endemic to the state of Hawai'i and is found on the islands of Hawaii (island), Maui, Molokai, and Lanai. It is a member of the silversword alliance. Two subspecies have been described, with the nominate subspecies Dubautia scabra scabra being found only on Maui and Hawaii (island).

References

  1. 1 2 3 Flann, C (ed) 2009+ Global Compositae Checklist
  2. ↑ Candolle, Augustin Pyramus de. 1836. Prodromus Systematis Naturalis Regni Vegetabilis 5: 668
  3. ↑ Tropicos, Argyroxiphium DC.
  4. ↑ [B. Baldwin. Age and Rate of Diversification of the Hawaiian Silversword Alliance (Compositae). 1998.]
  5. ↑ [Raven, P. H. Biology of Plants. 1990]
  6. 1 2 3 Robichaux, Robert H.; Carr, Gerald D.; Liebman, Matt; Pearcy, Robert W. (1990). "Adaptive Radiation of the Hawaiian Silversword Alliance (Compositae- Madiinae): Ecological, Morphological, and Physiological Diversity". Annals of the Missouri Botanical Garden. 77 (1): 64–72. doi:10.2307/2399626. ISSN   0026-6493. JSTOR   2399626.
  7. ↑ [S. Carlquist. Anatomy of Tropical Alpine Plants. 1994.]
  8. 1 2 3 Krushelnycky, Paul D.; Loope, Lloyd L.; Giambelluca, Thomas W.; Starr, Forest; Starr, Kim; Drake, Donald R.; Taylor, Andrew D.; Robichaux, Robert H. (2013). "Climate-associated population declines reverse recovery and threaten future of an iconic high-elevation plant". Global Change Biology. 19 (3): 911–922. Bibcode:2013GCBio..19..911K. doi:10.1111/gcb.12111. PMID   23504847. S2CID   33617236.
  9. 1 2 Robichaux, Robert H.; Moriyasu, Patrice Y.; Enoka, Jaime H.; McDaniel, Sierra; Loh, Rhonda K.; Bio, Kealiʻi F.; Bakutis, Ane; Tunison, J. Timothy; Bergfeld, Steven T.; Perry, J. Lyman; Warshauer, Frederick R. (2017-09-01). "Silversword and lobeliad reintroduction linked to landscape restoration on Mauna Loa and Kīlauea, and its implications for plant adaptive radiation in Hawaiʻi". Biological Conservation. 213: 59–69. Bibcode:2017BCons.213...59R. doi:10.1016/j.biocon.2017.07.001. ISSN   0006-3207.
  10. ↑ "Hawaiian silversword alliance, UH Botany". www.botany.hawaii.edu. Retrieved 2022-03-02.
  11. ↑ Baldwin, Bruce G.; Wood, Kenneth R.; Freyman, William A. (October 2021). "Directionally biased habitat shifts and biogeographically informative cytonuclear discordance in the Hawaiian silversword alliance (Compositae)". American Journal of Botany. 108 (10): 2015–2037. doi: 10.1002/ajb2.1757 . ISSN   0002-9122. PMID   34694624. S2CID   239766898.
  12. 1 2 Landis, Michael J.; Freyman, William A.; Baldwin, Bruce G. (2018-10-09). "Retracing the Hawaiian silversword radiation despite phylogenetic, biogeographic, and paleogeographic uncertainty". Evolution. 72 (11): 2343–2359. doi:10.1111/evo.13594. ISSN   0014-3820. PMID   30198108. S2CID   52178628.
  13. ↑ Baldwin, Bruce G.; Wagner, Warren L. (June 2010). "Hawaiian angiosperm radiations of North American origin". Annals of Botany. 105 (6): 849–879. doi:10.1093/aob/mcq052. ISSN   1095-8290. PMC   2876002 . PMID   20382966.
  14. 1 2 Walker, Lawrence R.; Powell, Elizabeth Ann (1999-07-01). "Regeneration of the Mauna Kea silversword Argyroxiphium sandwicense (Asteraceae) in Hawaii". Biological Conservation. 89 (1): 61–70. Bibcode:1999BCons..89...61W. doi:10.1016/S0006-3207(98)00132-3. ISSN   0006-3207.
  15. ↑ Bruegmann, M. M.; Caraway, V. (2003). "Argyroxiphium kauense". The IUCN Red List of Threatened Species. Retrieved July 6, 2024.
  16. ↑ Caraway, V.; Keir, M. (2020). "Silversword Argyroxiphium sandwicense". The IUCN Red List of Threatened Species. Retrieved July 6, 2024.
  17. ↑ Carr, Gerald (1997-03-20). "Argyroxiphium virescens Hillebrand". Hawaiian Silversword Alliance. University of Hawaii. Archived from the original on 18 September 2009. Retrieved 2009-11-01.
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