Kahoolawe Lei: Hinahina Silversword – Habitat & Preservation
Silversword (Hinahina) is a native Hawaiian plant with the scientific name of Argyroxiphium sandwicense ssp. It grows up to 6 feet tall and blooms yellow flowers once every 40 years before dying. Its habitat is in the 8,000 – 10,000 ft range and is facing destruction due to Western contact and destructive mammals. The University of Arizona is leading reintroduction efforts in a fenced-in compound known as Kahinahina Road.
Hinahina (Silversword) – Habitat, Extinction Threat & Preservation
Did you know? The Hinahina, or silversword flower, blooms only once in its lifetime, anywhere from 20 to 90 years! It’s incredible to think about how long it takes to come to life and share its beauty with the world.
This flower is extraordinary, and it’s a wonder it even exists. Its life cycle is lengthy and complex, yet it can create something so delightful to behold. It’s a reminder of the beauty of nature and the power of patience.
The silversword flower has fascinated the Hawaiian natives for centuries and has a special part in their culture. We can marvel at its unique growth cycle, so next time you encounter one of these unique blooms, take a moment to appreciate its beauty and endurance!
The Hinahina flower is the official lei material of Kahoolawe Island.
Argyroxiphium sandwicense, the Hawaii silversword or Hinahina, is a flowering plant endemic to Hawaii. It is rare, threatened, and federally protected, and the two subspecies are separated by geography.
European colonizers introduced foreign cattle, sheep, and goats, which caused a dramatic reduction in silversword species and threatened its population to near extinction. Scientists are worried that the silversword may not survive the changing climate as it reproduces so slowly and will most likely go extinct soon.
There are two subspecies of Hinahina, which are separated by geography:
- Haleakala Silversword grows on the mountain Haleakala on the island of Maui.
- Mauna Kea Silversword grows on the mountain Mauna Kea on the Island of Hawaii.
Let’s take a look at each one individually.
Haleakala Silversword
The Haleakala Silversword (A. sandwicense subsp. macrocephalum) is a threatened species, as defined by the U.S. Fish and Wildlife Service since 1992. It is found predominantly on the island of Maui, growing on volcanic cinder on the dormant Haleakala volcano in Haleakala National Park, at altitudes of over 2,100 m. It is recognizable by its sword-like succulent leaves, covered with silver hairs, and its ability to withstand extreme high-altitude conditions, with the base of leaves raising the temperature of the shoot-tip leaves to 20°C. From July to October, the plant undergoes senescence, producing a tall stalk of maroon ray flowers, which are pollinated by flying insects. Seeds are critical to the species’ lifecycle.
In the past, visitors to the park often uprooted the plant for personal use, and goats often fed on it, damaging the delicate root structure. To protect the species, the National Park Service fenced out the crater and legally protected the plants from damage, which has led to a successful recovery of the species.
Mauna Kea Silversword
Mauna Kea Silversword (Argyroxiphium sandwicense subsp. sandwicense) is an endangered flowering plant found only on Hawaii’s Big Island. It is the crown jewel of Mauna Kea volcano, named after its location. The Hawaiian name is ʻahinahina. It is part of the silversword alliance, a group of 50 species in 3 genera, all endemic to Hawaii. This subspecies has evolved rapidly in isolated and unique ecological conditions in Hawaii.
This silversword is an erect, single-stemmed, or rarely branched woody herb which produces a globe-shaped cluster of silvery-green, sword-shaped leaves in a rosette. The leaves can store water as gel, which is rare among plant leaves. The flowering stalk is narrow, up to 3 meters in length, with up to 600 heads of pink to maroon flowers. The plant lives for 5-40 years and flowers from June to November.
The difference between the two Hinahina, the Mauna Kea Silversword and the Haleakala Silversword, is the location they grow in, primarily in inflorescence shape, as there are more ray florets in the Haleakalā plants.
Scientists believe the plants to have evolved from extinct species and reached Hawaii via birds, and then evolved to survive harsh subalpine conditions, but lack protection from grazing mammals, as there is a common trait in a broader range of Hawaiian botany where many species evolved without protective mechanisms, but the adaptation of intracellular water storage favored silverswords and tarweeds’ survival in the Hawaiian habitat.
The original habitat where this plant grows is a wind-swept, exposed alpine desert with thin, rocky, volcanic cinder soil at 2,600-3,800m altitude. Precipitation mainly comes from snowfall during the winter months, and the mean annual rainfall is less than 51-102 cm per year. There is no shade and freezing temperatures at night, but the plants still thrived in this seemingly inhospitable habitat for millennia.
Due to land use decisions, the introduction of cattle, sheep, goats, dogs, and pigs threatened the near-extinction of silversword plants. The feral sheep population rose after 1921, decimating native plants, and mouflon sheep were introduced in 1954, causing further depredation. In 1986, the silversword was declared a federal endangered species, with only 41 surviving in the wild by 2003.
Initial efforts were made to fence off the remaining plants and establish exclosures with individual wild plants to rescue and reintroduce the species. The state eliminated nearly all feral sheep and other predators in 1981, and the removal of mouflon sheep started in 1988.
Cultivation of the silversword began in the 1970s, with modest results due to the narrow genetic diversity evident in their offspring. A controlled crossing program was then initiated to increase genetic diversity, and controlled propagation was used to reintroduce seedlings with 80+% survivorship. Hand pollination was used to achieve fertilization and increase genetic exchange between the nursery and wild individuals.
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