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Silver sword - Haleakalā National Park
The Haleakalā silversword, Argyroxiphium sandwicense subsp. macrocephalum, has numerous sword-like succulent leaves covered with silver hairs. Silversword plants in general grow on volcanic cinder, a dry, rocky substrate that is subject to freezing temperatures and high winds. The skin and hairs are strong enough to resist the wind and freezing temperature of this altitude and protect the plant from dehydration and the sun.
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. The leaves are arranged so that they and the hairs of the leaves can raise the temperature of the shoot-tip leaves up to 20 °C (36 °F), thereby having adapted to the extreme high-altitude temperatures by focusing the sunlight to converge at this point and warm the plant.
The other subspecies, Argyroxiphium sandwicense subsp. sandwicense (Mauna Kea silversword), is found on Mauna Kea. They differ primarily in the inflorescence shape—broader in the Haleakalā plants (less than 4 times as long as wide), and narrower on Mauna Kea (4.3-8.6 times as long as wide). The Haleakalā subspecies also generally has more ray florets, 11-42 versus 5-20 for Mauna Kea
Silver sword - Haleakalā National Park
The Haleakalā silversword, Argyroxiphium sandwicense subsp. macrocephalum, has numerous sword-like succulent leaves covered with silver hairs. Silversword plants in general grow on volcanic cinder, a dry, rocky substrate that is subject to freezing temperatures and high winds. The skin and hairs are strong enough to resist the wind and freezing temperature of this altitude and protect the plant from dehydration and the sun.
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. The leaves are arranged so that they and the hairs of the leaves can raise the temperature of the shoot-tip leaves up to 20 °C (36 °F), thereby having adapted to the extreme high-altitude temperatures by focusing the sunlight to converge at this point and warm the plant.
The other subspecies, Argyroxiphium sandwicense subsp. sandwicense (Mauna Kea silversword), is found on Mauna Kea. They differ primarily in the inflorescence shape—broader in the Haleakalā plants (less than 4 times as long as wide), and narrower on Mauna Kea (4.3-8.6 times as long as wide). The Haleakalā subspecies also generally has more ray florets, 11-42 versus 5-20 for Mauna Kea