The taxon declined markedly in the 1800s and early 1900s due to human vandalism (climbers dug up and brought back plants to show they had reached the summit) and to browsing by goats and cattle, and reached a low point in the 1920s. A reasonable estimate of the population size made in 1935 was 4,000 individuals. The taxon has rebounded since then due to protection measures, and deserves attention as one of the great conservation success stories in the Hawaiian Islands. There are currently seven known subpopulations. The population is estimated to number about 65,000 individuals and is increasing.
Regularity: Regularly occurring
Global Range: Current range: East Maui. Historically no additional range.
Catalog Number: US 59690
Collection: Smithsonian Institution, National Museum of Natural History, Department of Botany
Verification Degree: Original publication and alleged type specimen examined
Preparation: Pressed specimen
Collector(s): Wilkes Explor. Exped.
Locality: Haleakala., Maui, Hawaii, United States, Hawaiian Archipelago, Pacific Islands
Habitat and Ecology
Occurs in dry alpine desert; occasionally also in dry to moist subalpine shrublands (2,100–3,000 m). Found on cinder cone slopes, cinder fields, lava flows, in rocky gulches and on cliffs.
Comments: Subalpine shrublands and alpine cinder deserts. On cinder cones and cinder fields, on cliffs, and on old lava flows.
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 6 - 20
Comments: 6 current (1982-1997) and 2 historical occurrences.
IUCN Red List Assessment
Red List Category
Red List Criteria
- Needs updating
However, the taxon has an extremely restricted range (1,000 ha) and could easily be severely impacted by the loss of pollinators (through competition with the invasive Argentine ant) or any other catastrophic event. Direct human threats are currently controlled within the National Park, but as visitor numbers increase, so those threats could grow.
National NatureServe Conservation Status
Rounded National Status Rank: N2 - Imperiled
NatureServe Conservation Status
Rounded Global Status Rank: T2 - Imperiled
Reasons: This subspecies is restricted to the subalpine and alpine deserts of Haleakala on East Maui. The taxon declined markedly in the 1800's and early 1900's, and reached a low point in the 1920's. The taxon has rebounded since then, and is now estimated to number 50,000 plants. All of the extant plants are within Haleakala National Park. The major threats to the taxon are overcollection and vandalism by humans, and trampling and predation by goats. The national park has been fenced to exclude goats, but the threat remains due to the possibility of ingress.
Date Listed: 05/15/1992
Lead Region: Pacific Region (Region 1)
Listing status: T
For most current information and documents related to the conservation status and management of Argyroxiphium sandwicense macrocephalum, see its USFWS Species Profile
Comments: Threats include goats and larvae of endemic fly.
Biological Research Needs: Population biology and ecology, especially threat from insect infestation and extent of sexual reproduction.
Argyroxiphium sandwicense subsp. macrocephalum
Argyroxiphium sandwicense subsp. macrocephalum, the Haleakalā silversword, is a rare plant, part of the daisy family Asteraceae. The silversword in general is referred to as ʻāhinahina in Hawaiian (literally, "very gray").
The Haleakalā silversword is found on the island of Maui at elevations above 2,100 metres (6,900 ft) on the dormant Haleakalā volcano — on the summit depression, the rim summits, and surrounding slopes — in Haleakalā National Park. The Haleakalā silversword has been a threatened species 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. Since strict monitoring and governmental protection took effect, the species' recovery is considered a successful conservation story, although threats remain.
The Haleakalā silversword, Argyroxiphium sandwicense subsp. macrocephalum, has numerous sword-like succulent 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 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 life—which 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 (36 °F), thereby 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. They differ primarily in the inflorescence shape—broader 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.
At senescence, which often occurs when the plant reaches a diameter of approximately 0.5 metres (1.6 ft), the plant produces a tall stalk of maroon ray flowers which resemble the sunflower in just a few weeks. Flowering usually occurs from July through October. The leaves become limp and dry as the monocarpic 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 2 metres (6.6 ft) 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 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.
- Wagner, W. L., D. R. Herbst, and S. H. Sohmer (1990). Manual of the Flowering Plants of Hawaii. Honolulu: University of Hawaii Press.
- Plants of Hawaii: Argyroxiphium sandwicense subsp. macrocephalum
|This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (July 2009)|
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—Argyroxiphium sandwicense subsp. macrocephalum.
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