Hawaiian silversword  (Argyroxiphium sandwicense)

Classified as Vulnerable (VU) on the IUCN Red List (1). Subspecies: Argyroxiphium sandwicense sandwicense classified as Critically Endangered (CR), and A. s. macrocephalum classified as Vulnerable (VU) (1).

The striking Hawaiian silversword stands out starkly against the volcanic landscape of its habitat. This plant consists of a rosette of narrow, pointed silver leaves that may be up to 40 centimetres long (2), together forming a silvery sphere (3). The common name for this species comes from the shape of the leaves; these are stiff, narrowly sword-shaped, and covered with silky, silver hair (2). These plants are particularly dramatic when in flower; the tall inflorescence grows up from the rosette of leaves and may reach three metres tall, and 75 centimetres wide (2). Between 50 and 600 compound flower heads are carried on the inflorescence; the individual flowers are pink or wine red in colour (2). Two subspecies are recognised; Argyroxiphium sandwicense subsp. macrocephalum has a more elliptical-looking inflorescence than A. s. subsp. sandwicense, which is thicker (2).

Endemic to Hawaii, Argyroxiphium sandwicense macrocephalum is found on the island of Maui upon the Haleakala volcano, whilst A. s. sandwicense is found on Mauna Kea on the island of Hawaii itself (2).

Inhabits alpine cinder deserts, on Hawaiian volcanoes at heights of between 2,125 and 3,750 metres above sea level (2).

These plants only flower once in their lifetime, the silver rosettes grow for a number of years before the inflorescence ascends skywards (3). Flowers appear from mid-June to November (2), and after the seeds have been shed the whole plant dies (4). These exotic-looking plants are ideally suited to their harsh environment; the silver leaves reflect the sun's rays whilst their shape prevents moisture loss and protects the more delicate centre of the plant from predation (4).

These attractive plants were previously collected as curiosities; climbers on the mountains would dig them up as proof that they had reached the summit (5). Populations were further depleted by browsing and trampling by goats and cattle in the area (3). Today A. s. sandwicense is restricted to a single population of as few as 30 plants in the Wailuku River basin on Mauna Kea in Hawaii (2). 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 Hawaiian silversword is protected in Hawaii; A. s. sandwicense is listed as Endangered by the U.S. Fish and Wildlife Service whilst A. s. macrocephalum is listed as Threatened (6). On the island of Maui, the silversword is found within the Haleakala National Park, which was designated as an International Biosphere Reserve in 1980 (7). The U.S. Fish and Wildlife Service has produced Action Plans for the conservation of each subspecies (6), and the Haleakeala silversword has shown encouraging signs of recovery since it was first protected in the 1930s (5). This species is one of the many rare plants and animals found within the lunar landscape of the Haleakeala crater and can act as an important flagship species for conservation in the area (6).

For more information on the Hawaiian silversword see:

• U.S. Fish and Wildlife Service
  www.fws.gov/endangered
• NatureServe Explorer
  www.natureserve.org