EPOW - Ecology Picture of the Week

Mauna Kea Silversword (Argyroxiphium s. sandwicense), Family Asteraceae
Mauna Kea, Big Island, Hawaii

Explanation:  This week we are hiking at 10,000 feet elevation, right at treeline on the steep rocky upper slopes of Mauna Kea volcano on Big Island, Hawaii.  Loose volcanic rock crumbles underfoot, and before us spreads a spectacular example of a silversword ... an endangered native plant of these islands.  

Silverswords belong to an alliance of three genera -- Argyroxiphium, Dubautia, and Wilkesia, of the sunflower family -- which constitutes upwards of 30 endemic species.  They originally derived from a single ancestral tarweed species that somehow made it to the islands long ago, that then evolved into many separate species.  It is a stellar example of adaptive radiation.  

Silverswords are so named because the leaves are covered with fine silvery hairs that help ward off damage from harsh, high-elevation sunlight and that trap dew and fog drip.  The overall shape of the plant -- a short rosette of fleshy leaves -- is adapted to the cold winds.    

This particular example of a silversword is part of a reintroduction program here on Mauna Kea.  It was planted within an exclosure fence built to prevent trampling by cattle and nibbling by wild pigs that have ravaged much of the native vegetation in the middle elevations of this mountain.  All of the Argyroxiphium silversword species are endangered with extinction, making this reintroduction effort so important.  The specimens here are doing well so far, in this harsh highland environment. 

Sometime species of the silversword alliance occasionally hybridize with each other across genera, such as the Haleakala silversword (in the genus Argyroxiphium) and the na'ena'e (in the genus Dubautia), making it important to ensure that these reintroduced plants remain genetically pure.   

We are at a site known as Pu'u La'au, and I am being guided by special permission from the Hawaii Department of Land and Natural Resources to view this area.  The landscape here at treeline and above is astounding -- red, rusty, orange, and brown lava cinder cones punctuate vast barren valleys and tilt up into the clouds across wide volcanic valleys.  

Information:
    Merlin, M. 1995. Hawaiian forest plants. Pacific Guide Books, Honolulu, Hawaii. 80 pp.
    Sohmer, S. H., and R. Gustafson. 1987. Plants and flowers of Hawai'i. University of Hawaii Press, Honolulu, Hawaii. 160 pp.

Acknowledgment:
    My special thanks to USDI Fish and Wildlife biologist Dr. Paul Snowcroft for inviting me on this outing and guiding me to this site.