Argyroxiphium
Encyclopedia
Argyroxiphium is a small genus of five species in the sunflower
family, Asteraceae
. Its members are known by the common name 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
.
are endemic to Hawaii
, occurring only on the islands of Maui
and Hawaii
in an extremely localized distribution. They are primarily found above 1500 m (4,921.3 ft) in elevation in alpine deserts
or bogs, indicating an adaptation to low-nutrient soil
s. The Kaū 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
shrub
s 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 (Eke 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.
s they grow in. The succulent leaves are eaten by goat
s 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
. 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
.
Sunflower
Sunflower is an annual plant native to the Americas. It possesses a large inflorescence . The sunflower got its name from its huge, fiery blooms, whose shape and image is often used to depict the sun. The sunflower has a rough, hairy stem, broad, coarsely toothed, rough leaves and circular heads...
family, Asteraceae
Asteraceae
The Asteraceae or Compositae , is an exceedingly large and widespread family of vascular plants. The group has more than 22,750 currently accepted species, spread across 1620 genera and 12 subfamilies...
. Its members are known by the common name of silversword or greensword due to their long, narrow leaves and the silvery hairs on some species. It belongs to a larger radiation
Adaptive radiation
In evolutionary biology, adaptive radiation is the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage. Starting with a recent single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different...
of over 50 species, including the physically different genera Dubautia
Dubautia
Dubautia is a genus of flowering plant in the sunflower family, Asteraceae, that is endemic to Hawaii. It contains more species than the other two genera in the silversword alliance, including cushion plants, shrubs, trees, and lianas.-Selected species:...
and Wilkesia
Wilkesia
Wilkesia is a genus of flowering plants in the daisy family, Asteraceae. It contains two perennials, both of which are endemic to the island of Kauai in Hawaii. Wilkesia is a component of the silversword alliance.-Species:...
. This grouping is often referred to as the silversword alliance
Silversword alliance
Silversword alliance refers to an adaptive radiation of over 50 species in the composite or sunflower family, Asteraceae. The group is endemic to Hawaii, and is derived from a single immigrant to the islands...
.
Description
These perennialsPerennial plant
A perennial plant or simply perennial is a plant that lives for more than two years. The term is often used to differentiate a plant from shorter lived annuals and biennials. The term is sometimes misused by commercial gardeners or horticulturalists to describe only herbaceous perennials...
are endemic to Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
, occurring only on the islands of Maui
Maui
The island of Maui is the second-largest of the Hawaiian Islands at and is the 17th largest island in the United States. Maui is part of the state of Hawaii and is the largest of Maui County's four islands, bigger than Lānai, Kahoolawe, and Molokai. In 2010, Maui had a population of 144,444,...
and Hawaii
Hawaii (island)
The Island of Hawaii, also called the Big Island or Hawaii Island , is a volcanic island in the North Pacific Ocean...
in an extremely localized distribution. They are primarily found above 1500 m (4,921.3 ft) in elevation in alpine deserts
Hawaiian tropical high shrublands
The Hawaiian tropical high shrublands are a tropical savanna ecoregion in the Hawaiian Islands. They cover an area of on the upper slopes of the volcanoes Mauna Kea, Mauna Loa, Hualālai, and Haleakalā. It includes open shrublands, grasslands, and deserts...
or bogs, indicating an adaptation to low-nutrient 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...
s. The Kaū or Mauna Loa Silversword (A. kauense
Argyroxiphium kauense
The Mauna Loa silversword is a rare species of flowering plant in the Asteraceae family. It is endemic to the eastern and southern slopes of Mauna Loa on the island of Hawaii. A. kauense occurs in a much broader range of habitats than the closely related and better-known Haleakalā silversword...
) is the most adaptable: it can be found in rocky lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
flows, bogs, and open forest.
They consist of rosette
Rosette (botany)
In botany, a rosette is a circular arrangement of leaves, with all the leaves at a single height.Though rosettes usually sit near the soil, their structure is an example of a modified stem.-Function:...
-forming epigeal
Epigeal
Epigeal, epigean, epigeic and epigeous are biological terms describing an organism's activity above the soil surface.In botany, a seed is described as epigeal when the cotyledons of the germinating seed expand, throw off the seed shell and become photosynthetic above the ground...
shrub
Shrub
A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...
s 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 (Eke Silversword
Argyroxiphium caliginis
The Eke Silversword is a species of flowering plant in the sunflower family, Asteraceae. It is found only in two bogs in West Maui, Hawaii. The species is threatened by damage to the bogs by rooting feral pigs, but the main population at Eke Crater is now protected by fencing....
, greenswords). The flower
Flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...
heads consist of a ring of pistillate
Gynoecium
Gynoecium is most commonly used as a collective term for all carpels in a flower. A carpel is the ovule and seed producing reproductive organ in flowering plants. Carpels are derived from ovule-bearing leaves which evolved to form a closed structure containing the ovules...
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
Pollinator
A pollinator is the biotic agent that moves pollen from the male anthers of a flower to the female stigma of a flower to accomplish fertilization or syngamy of the female gamete in the ovule of the flower by the male gamete from the pollen grain...
, many plants must flower at the same time in relatively close proximity or they will fail to set 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...
. 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
Dubautia
Dubautia is a genus of flowering plant in the sunflower family, Asteraceae, that is endemic to Hawaii. It contains more species than the other two genera in the silversword alliance, including cushion plants, shrubs, trees, and lianas.-Selected species:...
. 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 cinderCinder
A cinder is a pyroclastic material. Cinders are extrusive igneous rocks. Cinders are similar to pumice, which has so many cavities and is such low-density that it can float on water...
s they grow in. The succulent leaves are eaten by goat
Goat
The domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the Bovidae family and is closely related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over three hundred distinct breeds of...
s 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
Argyroxiphium virescens
Argyroxiphium virescens was a species of flowering plant in the Asteraceae family.It was found only in the Hawaiian Islands.Its natural habitats were subtropical or tropical moist montanes and subtropical or tropical high-altitude shrubland....
) is apparently extinct, but in 1989 plants were discovered that appear to be hybrids between it and the Haleakalā Silversword
Haleakala Silversword
The Haleakalā silversword is a rare plant, part of the family Asteraceae. The silversword in general is referred to as āhinahina in Hawaiian...
. 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
Hawaii Volcanoes National Park
Hawaii Volcanoes National Park, established in 1916, is a United States National Park located in the U.S. State of Hawaii on the island of Hawaii. It encompasses two active volcanoes: Kīlauea, one of the world's most active volcanoes, and Mauna Loa, the world's most massive volcano...
.
Species
- Argyroxiphium caliginisArgyroxiphium caliginisThe Eke Silversword is a species of flowering plant in the sunflower family, Asteraceae. It is found only in two bogs in West Maui, Hawaii. The species is threatened by damage to the bogs by rooting feral pigs, but the main population at Eke Crater is now protected by fencing....
C.N.ForbesCharles Noyes Forbes-Biography:Forbes was born in Boylston, Massachusetts on 24 September 1883. When he was at the University of California he worked as a cadet for the emergency service during the 1906 San Francisco earthquake. From 1908 to 1920 he was curator of Botany at the Bernice P. Bishop Museum in Honolulu...
– Eke Silversword - Argyroxiphium grayanumArgyroxiphium grayanumArgyroxiphium grayanum, commonly known as the greensword, is a species of flowering plant in the sunflower 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.The silversword...
(Hillebr.William HillebrandWilliam Hillebrand was a German physician. He traveled the world, including over 20 years in the Hawaiian islands. In 1850, Hillebrand lived at what is now Foster Botanical Garden in Honolulu. He also became known as a botanist.-Life and career:...
) O. Deg.Otto DegenerOtto Degener was a botanist and conservationist who specialized in identifying plants of the Hawaiian Islands.-Life:Otto Degener was born May 13, 1899 in East Orange, New Jersey. Degener graduated from the Massachusetts Agricultural College...
– Greensword - Argyroxiphium kauenseArgyroxiphium kauenseThe Mauna Loa silversword is a rare species of flowering plant in the Asteraceae family. It is endemic to the eastern and southern slopes of Mauna Loa on the island of Hawaii. A. kauense occurs in a much broader range of habitats than the closely related and better-known Haleakalā silversword...
(RockJoseph RockJoseph Francis Charles Rock was an Austrian-American explorer, geographer, linguist and botanist.-Life:He was born in Vienna, Austria, but emigrated to the United States in 1905 and moved to Honolulu, Hawaii in 1907, where he eventually became an authority on the flora there...
& M.Neal) O.Deg.Otto DegenerOtto Degener was a botanist and conservationist who specialized in identifying plants of the Hawaiian Islands.-Life:Otto Degener was born May 13, 1899 in East Orange, New Jersey. Degener graduated from the Massachusetts Agricultural College...
& I.Deg. – Mauna Loa or Kaū Silversword - Argyroxiphium sandwicenseArgyroxiphium sandwicenseThe plant species Argyroxiphium sandwicense is a kind of silversword. It is endemic to Hawaii. There are two subspecies which are separated by geography. Both subspecies are rare, threatened, and federally protected....
DC. – Silversword- Argyroxiphium sandwicense ssp. sandwicense DC. – Mauna Kea SilverswordMauna Kea silverswordThe Mauna Kea silversword is a highly endangered flowering plant endemic to the Big Island of Hawaii. It is the "crown jewel" of the volcanic mountain, Mauna Kea, from which it derives its common name, and where it was once common. Extraordinary plant conservation efforts are being made to...
- Argyroxiphium sandwicense ssp. macrocephalum (A.GrayAsa Gray-References:*Asa Gray. Dictionary of American Biography. American Council of Learned Societies, 1928–1936.*Asa Gray. Encyclopedia of World Biography, 2nd ed. 17 Vols. Gale Research, 1998.*Asa Gray. Plant Sciences. 4 vols. Macmillan Reference USA, 2001....
) Meyrat – Haleakalā SilverswordHaleakala SilverswordThe Haleakalā silversword is a rare plant, part of the family Asteraceae. The silversword in general is referred to as āhinahina in Hawaiian...
- Argyroxiphium sandwicense ssp. sandwicense DC. – Mauna Kea Silversword
- Argyroxiphium virescensArgyroxiphium virescensArgyroxiphium virescens was a species of flowering plant in the Asteraceae family.It was found only in the Hawaiian Islands.Its natural habitats were subtropical or tropical moist montanes and subtropical or tropical high-altitude shrubland....
Hillebr. – East Maui Greensword (extinct)