''Argyroxiphium sandwicense'' subsp. ''macrocephalum'', the east Maui silversword or Haleakala silversword, is a rare plant, part of the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Asteraceae The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae w ...

. The silversword in general is referred to as ''āhinahina'' in Hawaiian (literally, "very gray").

Distribution

The Haleakala silversword is found on the island of

Maui The island of Maui (; Hawaiian: ) is the second-largest of the islands of the state of Hawaii at 727.2 square miles (1,883 km2) and is the 17th largest island in the United States. Maui is the largest of Maui County's four islands, which ...

at elevations above on the dormant Haleakalā

volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates are ...

on the summit depression, the rim summits, and surrounding slopesin

Haleakalā National Park Haleakalā National Park is an American national park located on the island of Maui in the state of Hawaii. Named after Haleakalā, a dormant volcano within its boundaries, the park covers an area of , of which is a wilderness area. The land wa ...

. The Haleakala silversword has been a

threatened species Threatened species are any species (including animals, plants and fungi) which are vulnerable to endangerment in the near future. Species that are threatened are sometimes characterised by the population dynamics measure of ''critical depensa ...

as defined by the U.S. Fish and Wildlife Service, since May 15, 1992. Prior to that time, excessive grazing by cattle and goats, and vandalism inflicted by people in the 1920s, had caused its near

extinction Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

. Since strict monitoring and governmental protection took effect, the species' recovery is considered a successful conservation story, although threats remain.

Description

The Haleakala silversword, ''Argyroxiphium sandwicense'' subsp. ''macrocephalum'', has numerous sword-like

succulent In botany, succulent plants, also known as succulents, are plants with parts that are thickened, fleshy, and engorged, usually to retain water in arid climates or soil conditions. The word ''succulent'' comes from the Latin word ''sucus'', meani ...

leaves covered with silver hairs. Silversword plants in general grow on volcanic cinder, a dry, rocky substrate that is subject to freezing temperatures and high winds. The skin and hairs are strong enough to resist the wind and freezing temperature of this altitude and protect the plant from

dehydration In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...

and the sun. The plant's base of leaves, arranged in a spherical formation at ground level of the plant, dominates for the majority of the plant's lifewhich may be greater than 50 years. The leaves are arranged so that they and the hairs of the leaves can raise the temperature of the shoot-tip leaves up to 20^o C (68^o F), having adapted to the extreme high-altitude temperatures by focusing the sunlight to converge at this point and warm the plant. The other subspecies, ''Argyroxiphium sandwicense'' subsp. ''sandwicense'' (Mauna Kea silversword), is found on

Mauna Kea Mauna Kea ( or ; ; abbreviation for ''Mauna a Wākea''); is a dormant volcano on the island of Hawaii. Its peak is above sea level, making it the highest point in the state of Hawaii and second-highest peak of an island on Earth. The peak is ...

. They differ primarily in the inflorescence shapebroader in the Haleakalā plants (less than 4 times as long as wide) and narrower on Mauna Kea (4.3–8.6 times as long as wide). The Haleakala subspecies also generally has more ray florets, 11–42 versus 5–20 for Mauna Kea.Wagner, W. L., D. R. Herbst, and S. H. Sohmer (1990). Manual of the Flowering Plants of Hawaii. Honolulu: University of Hawaii Press.

Lifecycle

senescence Senescence () or biological aging is the gradual deterioration of functional characteristics in living organisms. The word ''senescence'' can refer to either cellular senescence or to senescence of the whole organism. Organismal senescence inv ...

, which often occurs when the plant reaches a diameter of approximately , the plant produces a tall stalk in just a few weeks of maroon ray flowers which resemble the

sunflower The common sunflower (''Helianthus annuus'') is a large annual forb of the genus ''Helianthus'' grown as a crop for its edible oily seeds. Apart from cooking oil production, it is also used as livestock forage (as a meal or a silage plant), as ...

. Flowering usually occurs from July through October.Plants of Hawaii: ''Argyroxiphium sandwicense'' subsp. ''macrocephalum''
/ref> The leaves become limp and dry as the

monocarpic Monocarpic plants are those that flower and set seeds only once, and then die. The term is derived from Greek (''mono'', "single" + ''karpos'', "fruit" or "grain"), and was first used by Alphonse de Candolle. Other terms with the same meaning are ...

plant then goes to seed and dies. The flowering stalk may have up to 600 heads of up to 40 outlying ray flowers and 600 disk flowers and is pollinated by flying insects like '' Hylaeus'' ('' Nesoprosopis'') ''volcanicus''. The flower stalk can reach up to in height and has numerous tiny sticky hairs to prevent crawling insects from damaging the plant. Seeding is a critical time because damage to the flowers or stalk by insects before the seeds can mature can jeopardize the plant's entire reproductive output.

History and conservation

Before the

National Park Service The National Park Service (NPS) is an agency of the United States federal government within the U.S. Department of the Interior that manages all national parks, most national monuments, and other natural, historical, and recreational propertie ...

was granted control of Haleakalā volcano, visitors to the volcano's summit often participated in the common practice of uprooting a silversword plant and then rolling it on the jagged lava rock terrain, drying the flowers for arrangements, or using the plant as kindling. Because the delicate, shallow root structure can be crushed by walking in the rocks around the plant, they are very sensitive to foreign elements. Feeding by goats also severely damaged many plants and prevented reproduction. Ungulates are now fenced out of the crater area and the species is legally protected from damage by humans.

Gallery

File:Haleakala Silversword.jpg, Flower head bud, Haleakalā National Park. File:Silverswords on haleakala.JPG, Silverswords in bloom in Haleakalā crater File:Argyroxiphium sandwicense macroencephalum.jpg, Haleakalā silversword at summit of Haleakalā National Park, Maui. File:Dying Haleakala silversword.JPG, Dying Haleakalā silversword after blooming at Haleakalā National Park, Maui. File:Argyroxiphium_sandwicense_Haleakala.jpg, Multiple rosettes indicate this individual may have ''Dubautia'' genes, although it does not have the yellow flowers of most hybrids. File:Ahinahina flowers.jpg, Close-up of flowers. File:Haleakala-Silversword-Hawaii.jpg, Strong silver hairs cover the sword-like leaves.

References

Reference links

Ka’ahele Hawai’i Native PlantsFederal recovery plan

External links

USDA Plants Profile for ''Argyroxiphium sandwicense'' subsp. ''macrocephalum'' (Hawai'i silversword)
{{Taxonbar, from=Q5455727 sandwicense subsp. macrocephalum Endemic flora of Hawaii Biota of Maui Haleakalā National Park Plant subspecies