Argyroxiphium sandwicense DC.
Hawai'i Silversword, Hawaiian Silversword, Mauna Kea Silversword
Argyrophyton douglasii, Argyroxiphium sandwicense subsp. sandwicense, Argyroxiphium sandwicense var. sandwicense, Dubautia sandwicensis
This species is endemic to Hawaii. It grows only on the upper slopes of Mauna Kea at elevations between 8,530 and 12,470 feet (2,600 to 3,800 m).
Argyroxiphium sandwicense is a rare plant that forms a large ball-shaped rosette of numerous narrow, lance-shaped leaves coated with silvery hairs. The rosette grows up to 2.5 feet (75 cm) in diameter, usually solitary, but some specimens produce offsets and form a tight cluster of rosettes of various sizes. Leaves are up to 16 inches (40 cm) long and up to 0.6 inches (1.5 cm) broad.
The rosette may live from 3 to more than 50 years before flowering, flowers only once, and then die. Mature rosettes send up a spectacular, up to 10 feet (3) tall stalk with numerous short branches, each terminating in a single head of flowers in summer. The flower heads are up to 0.8 inches (2 cm) in diameter and have white to pink ray florets and pink to maroon disk florets. A rosette that flowers in the absence of other flowering rosettes can produce a few black achenes that contain a single seed.
USDA hardiness zone 10a to 10b: from 30 °F (−1.1 °C) to 40 °F (+4.4 °C).
How to Grow and Care
The silversword alliance is about 50 species of plants belonging to three genera endemic to the Hawaiian islands. They get their common name from the visually impressive silversword.
These plants only flower once in their lifetime. The silver rosettes grow for a number of years before the inflorescence ascends skywards. Flowers appear from mid-June to November, and the whole plant dies after the seeds have been shed. These exotic-looking plants are ideally suited to their harsh environment. The silver leaves reflect the sun's rays while their shape prevents moisture loss and protects the more delicate center of the plant from predation.
These attractive plants were previously collected as curiosities. Climbers on the mountains would dig them up as proof that they had reached the summit. Populations were further depleted by browsing and trampling by goats and cattle in the area. Today Argyroxiphium sandwicense is restricted to a single population of as few as 30 plants in the Wailuku River basin on Mauna Kea in Hawaii. These plants are at risk from the small size and range of their population, which is vulnerable to any chance event that might occur.
The Hawai'i Silversword is protected in Hawaii.
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