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

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Asteraceae Asteraceae () is a large family (biology), family of flowering plants that consists of over 32,000 known species in over 1,900 genera within the Order (biology), order Asterales. The number of species in Asteraceae is rivaled only by the Orchi ...

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

Distribution

The Haleakalā silversword is found on the island of

Maui Maui (; Hawaiian language, Hawaiian: ) is the second largest island in the Hawaiian archipelago, at 727.2 square miles (1,883 km2). It is the List of islands of the United States by area, 17th-largest in the United States. Maui is one of ...

at elevations above on the dormant

Haleakalā Haleakalā (; Hawaiian: ), or the East Maui Volcano, is a massive, active shield volcano that forms more than 75% of the Hawaiian Islands, Hawaiian Island of Maui. The western 25% of the island is formed by another volcano, Mauna Kahalawai, als ...

volcano A volcano is commonly defined as a vent or fissure 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 oft ...

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

Haleakalā National Park Haleakalā National Park is a List of national parks of the United States, national park of the United States located on the island of Maui, Hawaii. Named after Haleakalā, a dormant volcano within its boundaries, the park covers an area of , of w ...

. The Haleakalā silversword has been a

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

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 an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

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

Description

The Haleakalā 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 Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

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 that disrupts metabolic processes. It occurs when free water loss exceeds intake, often resulting from excessive sweating, health conditions, or inadequate consumption of water. Mild deh ...

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 °C (68 °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 (, ; abbreviation for ''Mauna a Wākea''); is a dormant Shield volcano, shield volcano on the Hawaii (island), island of Hawaii. Its peak is above sea level, making it the List of U.S. states by elevation, highest point in Hawaii a ...

. 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 Haleakalā 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 Function (biology), functional characteristics in living organisms. Whole organism senescence involves an increase in mortality rate, death rates or a decrease in fecundity with ...

, 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 species of large annual forb of the daisy family Asteraceae. The common sunflower is harvested for its edible oily seeds, which are often eaten as a snack food. They are also used in the pr ...

. 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 (', "single" + , "fruit" or "grain"), and was first used by Alphonse de Candolle. Other terms with the same meaning are '' hapaxanth'' ...

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 List of federal agencies in the United States, agency of the Federal government of the United States, United States federal government, within the US Department of the Interior. The service manages all List ...

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 Ungulates ( ) are members of the diverse clade Euungulata ("true ungulates"), which primarily consists of large mammals with hooves. Once part of the clade "Ungulata" along with the clade Paenungulata, "Ungulata" has since been determined to b ...

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