Photos Courtesy of Forest and Kim Starr
Director’s Series at the Arnold Arboretum ~ Last night I had the pleasure of attending Robert Robichaux’s splendid lecture Restoring Hawaii’s Marvels of Evolution, presented at the Hunnewell Building of the Arnold Arboretum. Especially fascinating are examples of adaptive radiation, in which a singular North American mainland plant arrived on the islands and evolved into an array of different species, exhibiting fantastic variation in form and habitat.
See related post What is Adaptive Radiation?
Mr. Robchauxi gave detailed information on the restoration efforts of the Haleakalā Silversword (Argyroxiphium sandwicense subsp. macrocephalum), perhaps Hawaii’s most famous native flowering plant, along with providng examples of other silversword species and lobeliads.
A relative of the sunflower, Haleakalā Silversword may live for several decades, however it is monocarpic, meaning once-flowering, after which it dies. Flowering usually occurs from June through October and the single stalk may contain as many as 600 heads with up to 40 ray flowers surrounding approximately 600 disk florets. Haleakalā Silversword is found only on the island of Maui. The plant’s common name is derived from the genera’s numerous sword-like succulent leaves, which are covered with silver hairs. Since May of 1992, the Haleakalā Silversword has been considered a threatened species by the U.S. Fish and Wildlife Service.
The silversword alliance refers to an adaptive radiation of over 5o Hawaiian species in the composite or sunflower family, Asteraceae, Tribe: Madieae (genera Dubautia, Wilkesia, and Agyroxiphium), and also to the Hawaiian Silversword Alliance Project (HSA), an adaptive evolution study project that is a collaborative effort among scientists at multiple public, private, and government institutions.
Species: A. sandwicense
Subspecies: A. s. subs. macrocephalum