Mauna Kea Silversword
Mauna Kea Silversword
Argyroxiphium sandwicense ssp. sandwicense
|Listed||March 21, 1986|
|Description||A perennial plant growing from a rosette of stiff, succulent, silvercolored, sword-like leaves.|
|Habitat||Volcanic soil at high elevation.|
|Reproduction||A perennial plant, flowering once after a growth period of from several to more than 50 years, with new plants established as seedlings.|
|Threats||Introduced mammalian herbivores, as well as excessive collecting, wildfire, and predation of its pollinators by an introduced species of ant.|
The Mauna Kea silversword, also known as the ahinahina, is an erect, perennial, usually single-stemmed (or sometimes branched) plant. Its leaves occur as a dense cluster at the base of the plant; this basal rosette can be about 2 ft (60 cm) wide. The erect flowering stem can be as tall as 9 ft (almost 3 m). Individual leaves are sword-like in shape, 6-16 in (15-40 cm) long, rigid, thick with succulent water-storing tissue, and covered with a dense, silvery colored, reflective mat of tiny hairs. The attractive flower heads consist of 50-600 maroon-colored disk florets (each floret is an individual flower, but they are aggregated into a composite, flower-like inflorescence, as is typical of the Asteraceae). Numerous of these composite flower heads are aggregated onto a columnar, erect, flowering stem. The Mauna Kea silversword is one of about 38 species of closely related species in the so-called "silversword alliance," which probably originated through an evolutionary radiation of a single species that colonized the Hawaiian archipelago in ancient times.
The Mauna Kea silversword is a perennial plant, which grows as a dense rosette for about three to 50 years until it has accumulated enough reserves of energy and nutrients to sustain a massive flowering effort, which is followed by seed dispersal and the death of the parent plant. This kind of once-only, "big-bang" reproduction is referred to as monocarpic or semelparous. The silversword is pollinated by native species of moths. The flowering season is mid-June to November. The seeds are spread by wind or water.
The Mauna Kea silversword occurs in high-elevation habitats at altitudes ranging from about 8,500-12,500 ft (2,600-3,800 m). Its general habitat is well-drained alpine scrub or cinder desert, with a substrate derived from volcanic rock and debris, and receiving 20-69 in (50-175 cm) of precipitation per year.
The Mauna Kea silversword is a locally evolved, or endemic species that is only known from the upper slopes of Mauna Kea, Hawaii. The Hawaiian archipelago has an extremely large fraction of endemic species in its flora; about 89% of the indigenous flowering plants occur nowhere else in the world.
The Mauna Kea silversword was once a much more abundant species with a wider distribution around Mauna Kea. Today, however, the remaining natural population consists of only about 50 plants occurring on precipitous cliffs in the upper reaches of the Wailuku River. In this steep habitat, the silversword is physically protected from non-native herbivorous mammals. About another 750 wild individuals occur in new populations established in suitable habitat within herbivore exclosures. The most important cause of the decline of the Mauna Kea silversword has been unsustainable browsing by introduced mammals, particularly feral goats. Because the silversword did not evolve in the presence of herbivores such as these, it is extremely vulnerable to this kind of biological damage. The Mauna Kea silversword is also potentially threatened by the invasion of its habitat by the Argentine ant (Iridomyrmex humilis ), which has been accidentally introduced to Hawaii and may be a devastating predator of the endemic, indigenous, insect pollinators of the rare plant. It is also potentially threatened by wildfire, trampling, and collection by people.
Conservation and Recovery
The slopes of Mauna Kea above about 7,900 ft (2,400 m) in elevation have been a Forest Reserve since 1909. The major objectives of management have been to protect the native plants from browsing by introduced mammals, trampling or collection by humans, and wildfire, while engaging in research and monitoring of the wild populations. Since 1935, the Hawaii Department of Land and Natural Resources has been preserving and enhancing the Mauna Kea silversword by building fenced exclosures. Since 1974 it has also been out-planting silverswords raised in captivity (in a facility in Hawaii Volcanoes National Park). Many of the wild-flowering silverswords must be hand-pollinated by botanists because they occur at too low a density for natural pollinators to be effective. The biology and ecology of the silversword are being studied by scientists associated with the Fish and Wildlife Service, the University of Hawaii (Manoa), the University of California (Davis), and the University of British Columbia, Vancouver.
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
National Biological Service
Haleakala National Park
P. O. Box 369
Makawao, Hawaii 96768
Robichaux, R.H., G.D. Carr, M. Liebman, and R.W. Pearcy. 1990. "Adaptive radiation of the silversword alliance (Compositae: Madiinae): ecological, morphological, and physiological diversity." Annals of the Missouri Botanical Garden 77:64-72.
U.S. Fish and Wildlife Service. 2000. "The Recovery Plan for the Mauna Kea Silversword." http://www.r1.fws.gov/pacific/wesa/mkeaslvrswrdidx.html