Description: Monocarpic plant taking 15 to 50 years to flowering. Leaves grow in a dense rosette close to the ground, 15–40 cm long and up to 1.5 cm wide, narrowly lanceolate, triangular in cross section, pointy, stiff and covered in silvery hairs for protection against high elevation UV radiation.
Flower scape rises from the leaves, erect, usually single, seldom branched, up to 3 m in height and 75 cm in diameter, inflorescence is a raceme of 50–600 heads, nodding, each with 11–42 ray florets, pale red to maroon, and 50–600 disc florets, 5–8 mm long, of similar colour. Fruit is an achene, 7–15 mm long.
After seeds ripen the plant dies.
Threat and protection: This taxon was almost extirpated in the past (goat grazing in the crater), however present population appears healthy with about 65 000 plants. The area of distribution is very limited and therefore, it is classified in the Red List IUCN as vulnerable (VU).
Argyroxiphium sandwicense subsp. macrocephalum is a clumping perennials with rosettes up to 20 inches (50 cm) in diameter, of numerous long, sword-like, succulent leaves covered with silver hairs.
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. A tall, stunning flower spike appears after many (15 to 50) years and then the plant dies.
Scientific Name
Argyroxiphium sandwicense subsp. macrocephalum (A.Gray) Meyrat
Common Names
Haleakala Silversword, East Maui Silversword
Synonyms
Argyroxiphium macrocephalum (basionym), Argyroxiphium sandwicense var. macrocephalum
Scientific Classification
Family: Asteraceae
Subfamily: Asteroideae
Tribe: Madieae
Subtribe: Helianthodae
Genus: Argyroxiphium
Hardiness
USDA hardiness zone 10a to 10b: from 30 °F (−1.1 °C) to 40 °F (+4.4 °C).
TIPS: to Grow and Care
The Silversword alliance is a group of about 50 species of plants belonging to three genera endemic to the Hawaiian islands. They get their common name from the visually impressive Silversword.
Distribution: Argyroxiphium sandwicense is endemic to Hawaiian Islands and it is found only on islands of Maui and Hawaii.
The nominate subspecies is found on the volcano of Mauna Kea on the Big Island (Hawaii) and the subspecies A. s. subsp. macrocephalum (in our pictures) on the volcano Haleakala on the island of Maui.
Ecology: Grows in the crater and on the outer top slopes of the volcano, on dry cliffs and edges of lava fields and on the rocks at high elevations of 2100 to 3000 m. Blooms from July to October.
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 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.
Protected in Hawaii.
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