Argyroxiphium sandwicense subsp. macrocephalum (A. Gray) Meyrat — Details

Haleakala Silversword learn more about names for this taxon

Overview

Distribution

National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

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Global Range: Current range: East Maui. Historically no additional range.

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Historic Range:
U.S.A. (HI)

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Physical Description

Type Information

Lectotype; Type collection for Argyroxiphium macrocephalum A. Gray
Catalog Number: US 59690
Collection: Smithsonian Institution, National Museum of Natural History, Department of Botany
Verification Degree: Original publication and alleged type specimen examined; 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
  • Lectotype: Keck, D. D. 1936. Occas. Pap. Bernice Pauhi Bishop Mus. 11: 17.; Gray, A. 1852. Proc. Amer. Acad. Arts. 2: 160.; Type collection: Keck, D. D. 1936. Occas. Pap. Bernice Pauhi Bishop Mus. 11: 17.; Gray, A. 1852. Proc. Amer. Acad. Arts. 2: 160.
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© Smithsonian Institution, National Museum of Natural History, Department of Botany

Source: National Museum of Natural History Collections

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Holotype for Argyroxiphium macrocephalum A. Gray
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
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© Smithsonian Institution, National Museum of Natural History, Department of Botany

Source: National Museum of Natural History Collections

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Ecology

Habitat

Comments: Subalpine shrublands and alpine cinder deserts. On cinder cones and cinder fields, on cliffs, and on old lava flows.

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Population Biology

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.

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Conservation

Conservation Status

National NatureServe Conservation Status

United States

Rounded National Status Rank: N2 - Imperiled

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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.

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Current Listing Status Summary

Status: Threatened
Date Listed: 05/15/1992
Lead Region:   Pacific Region (Region 1) 
Where Listed:


Population detail:

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

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Threats

Comments: Threats include goats and larvae of endemic fly.

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Management

Biological Research Needs: Population biology and ecology, especially threat from insect infestation and extent of sexual reproduction.

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Wikipedia

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").

Distribution[edit]

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.

Description[edit]

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.[1]

Lifecycle[edit]

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.[2] 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[edit]

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.

Gallery[edit]

See also[edit]

References[edit]

  1. ^ Wagner, W. L., D. R. Herbst, and S. H. Sohmer (1990). Manual of the Flowering Plants of Hawaii. Honolulu: University of Hawaii Press.
  2. ^ Plants of Hawaii: Argyroxiphium sandwicense subsp. macrocephalum

Reference links[edit]

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