Argyroxiphium

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silverswords
greenswords
File:Argyroxiphium sandwicense Haleakala.jpg
Haleakalā Silversword
Scientific classification
Kingdom:
Plantae
(unranked):
Angiosperms
(unranked):
Eudicots
(unranked):
Asterids
Order:
Asterales
Family:
Asteraceae
Subfamily:
Asteroideae
Tribe:
Madieae[1]
Genus:
Argyroxiphium
Synonyms[2]

Argyrophyton Hook.

Lua error in Module:Taxonbar/candidate at line 22: attempt to index field 'wikibase' (a nil value).

Argyroxiphium is a small genus of plants in the sunflower family, Asteraceae.[3][4] Its members are known by the common names of silversword or greensword due to their long, narrow leaves and the silvery hairs on some species. It belongs 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.

Description

These perennials are endemic to Hawaiʻi, occurring only on the islands of Maui and Hawaiʻi in an extremely localized distribution. They are primarily found above 1,500 m (4,900 ft) in elevation in alpine deserts or bogs, indicating an adaptation to low-nutrient soils. The Kaʻū or Mauna Loa Silversword (A. kauense) is the most adaptable: it can be found in rocky lava flows, bogs, and open forest.

They consist of rosette-forming epigeal shrubs or dwarf shrubs. They may consist of a single large rosette (Mauna Kea and Haleakalā silverswords), a short-branched rosette (Mauna Loa Silversword), or spreading with runners (ʻEke Silversword, greenswords). The flower heads consist of a ring of pistillate ray florets around 30 to 600 disk florets. The corolla varies in color from purplish to wine red or yellow, while the anthers are dark. A rosette will grow from 5–20 years before flowering, after which it dies. For those with a single rosette, this means the death of the plant (in contrast, those reproducing by runners rarely flower and may be very long-lived). Because they require cross-pollination by insects, many plants must flower at the same time in relatively close proximity or they will fail to set seed. A significant population must exist for enough to flower each year for pollination to occur.

Despite appearances, they are very closely related to the genus Dubautia. Although some Dubautia are radically different from silverswords, those found in wet forests and alpine deserts clearly grade into the form of silverswords. Hybrids between Argyroxiphium sandwicense and Dubautia menziesii are common in Haleakalā Crater. Although the two species are quite distinct, the hybrids span the entire range of variation between them.

Conservation

Silverswords and greenswords are highly sensitive to disturbance. Their shallow root systems are easily crushed in the boggy soil or loose volcanic cinders they grow in. The succulent leaves are eaten by goats in the dry summits, and pigs frequently disturb the fragile bog vegetation. All species are highly restricted in range, and even those that are protected are vulnerable to catastrophic events. 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.[5] The Mauna Kea and Mauna Loa silverswords both have small populations, but are being cultivated and outplanted in protected areas. The largest population of Mauna Loa Silverswords is in Kahuku, which was recently acquired by Hawaii Volcanoes National Park.[6]

Species

accepted species[2]
formerly included[2]

now in Dubautia

Gallery

  • Starr 980630-1521 Argyroxiphium grayanum.jpg

    Greensword

  • Greensword, Puʻu Kukui bog

  • Silversword Haleakala.jpg

    Haleakalā Silversword

  • Haleakala silversword.jpg

    Silversword in Haleakalā Crater

  • Dubautia-silversword hybrid in Haleakalā Crater

  • Starr 011205-0093 Argyroxiphium sandwicense subsp. sandwicense.jpg

    Mauna Kea Silversword

  • Mauna Kea silversword2.jpg

    Mauna Kea Silversword

  • Mauna Kea Silversword flowering

  • MaunaKeaSilversword.JPG

    Mauna Kea Silversword

  • Kahuku silversword habitat.jpg

    Mauna Loa Silversword habitat, Kahuku

  • Kahuku silversword1.jpg

    Mauna Loa Silversword, multiple rosettes

  • Kahuku silversword2.jpg

    Mauna Loa Silversword, single rosette

  • Silversword.jpg

    Haleakalā Silversword (close-up)

References

  1. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ 2.0 2.1 2.2 Flann, C (ed) 2009+ Global Compositae Checklist
  3. ↑ Candolle, Augustin Pyramus de. 1836. Prodromus Systematis Naturalis Regni Vegetabilis 5: 668
  4. ↑ Tropicos, Argyroxiphium DC.
  5. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ Flora of the Hawaiian Islands, Smithsonian Institution National Museum of Natural History,

External links

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