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Haleakala Silverswords

Haleakala National Park

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© Maui Downhill
'Ahinahina (Silverswords) - Argyroxiphium sandwicense subsp. macrocephalum
The Haleakala 'ahinahina, or silversword, is probably the most famous of the 28 species in the silversword alliance. Member of the silversword alliance are perhaps the most dramatic examples of adaptive radiation in the islands. These 28 species, and many subspecies, may have descended from a single ancestor, the California tarweed, which may have reached Hawaii millions of year ago. The 'ahinahina grows between 6,500 and 10,000 feet in elevation on the upper slopes of Haleakala where it has adapted to the harsh environment. The dense covering of silver hair on its slender leaves helps to conserve moisture and protect the plant from the sun's severe rays. The 'ahinahina is low growing and has a large taproot that helps to keep it secure in high winds. Smaller, shallow, fibrous roots extend out from the taproot and allow the 'ahinahina to collect water from the surrounding loose cinder. These small roots extend as far as six feet from the plant and are easily damaged by the weight of human footsteps. This is one reason off-trail travel is strictly prohibited in Haleakala National Park.

© N.P.S.
'Ahinahina with Young Blooming Stalk
The 'ahinahina begins pushing up a stalk in the summer. An individual 'ahinahina may bloom anywhere from 2 to 50 year after it has become established. However, the plant will bloom only once, for about two months, and then die. The length of time it takes to bloom may depend upon the available moisture and nutrients in the surrounding cinder and on atmospheric conditions.

© N.P.S.
Blooming 'Ahinahina at Silversword Loop
The Haleakala 'ahinahina is listed as threatened by the U.S. Fish and Wildlife Service due to several factors. In the early 1900's, 'ahinahina were pulled by the roots and gathered as souvenir by visitor who made the trip up Haleakala. The number of 'ahinahina growing in the Park further decreased with the introduction of foraging animals such as cattle and goats. Like most native Hawaiian plants, the 'ahinahina lacks adaptations to deter browsing, such as thorns, unpleasant textures, bitter tastes or harmful chemicals. 'Ahinahina populations declined to less than one thousand individuals. Park resource manager constructed a boundary fence to keep the goats, cattle and pigs out of the Park. The fencing program and prohibitions against human damage have allowed the species to recover. ~ Today the estimated population of Haleakala 'ahinahina is about 50,000.

© N.P.S.
'Ahinahina in Bloom
The 'ahinahina flower stalk is normally 2 to 6 feet tall, but can reach up to 8 feet. Hundreds of one to two inches wide purplish blossoms cover the stalk. As with other desert plants, having flower atop a tall stalk may be an adaptation to attract pollinators and later disperse seeds on the wind. The number of blooming plants per year varies. Some year there may be no 'ahinahina in bloom, while other year there may be over 6,000 blooming throughout the Park.

© N.P.S.
Silversword Flower
A close-up of an 'ahinahina blossom reveals lots of little flower that look similar to a sunflower. The 'ahinahina is a member of the sunflower family, whose flower heads are actually made up of several hundred disc and ray flower. 'Ahinahina cannot produce fertile seeds without cross-pollination. Therefore, these plants are dependent upon insect pollinator for long-term survival. Native moths, flies or bees travel in a circle around the perimeter of the blossom gathering pollen. Cross-pollination occur when the insect travels to the blossom of another 'ahinahina plant. The introduction of foreign insects, such as the Argentine ant, that prey on the native pollinator could result in a dramatic decrease in 'ahinahina populations.

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