Pua’ala  (Brighamia rockii)

Classified as Critically Endangered (CR - D) on the IUCN Red List 2004 (1). Listed as an endangered, endemic species under the U.S. Endangered Species Act 1992 (2).

The Pua’ala is one of two endangered Brighamia species endemic to Hawaii, the ‘olulu (B. insignis) and the pua’ala (B. rockii). These species are morphologically similar and considered amongst the most unusual of Hawaiian flora (3). A distinguishing feature is their tall succulent, usually un-branched stem, bulbous at the base and tapering towards the apex. The stem is crowned in a rosette of fleshy leaves and the fragrant flowers are trumpet-shaped (4). The flowers of pua’ala are white while those of the ‘olulu (B. insignis) are cream to yellow. During its juvenile stage the pua’ala has a distinctive purple stem, unlike the ‘olulu (B. insignis) (5).

Endemic to the Island of Molokai and historically on Maui and Lanai, the pua’ala exists in three sub-populations totalling less than 50 mature individuals (1).

The pua’ala is found on exposed steep coastal cliffs with native grasses, shrubs, and trees (1), from sea level to 470 meters elevation (5).

A perennial, succulent plant adapted to tolerate the salty environment of exposed sea-cliffs (3). Pua’ala blooms in the autumn (6). The fruit produced is a green capsule containing 20 to 60 seeds, which ripens six to eight weeks after pollination. Only 5% of the flowers produce pollen, and very few fruits are formed per inflorescence (5). The unusually low rate of fruit production is thought to be as a consequence of the presumed extinction of the pua’ala’s natural pollinator, believed to be a species of moth (6).

Once fairly common, the pua’ala is now at risk of extinction due to habitat degradation, predation by feral goats, and competition from introduced plant and animal species (4). Low reproductive rates, which exacerbate the problem by making recovery slow, could be due to low pollen production, low establishment of seedlings, and the decline of natural pollinators (5). An additional fear is low genetic variability, as a result of inbreeding between the few remaining plants, will mean failure to produce healthy seedlings able of responding to environmental change (4).

The Conservation Department of the National Tropical Botanical Garden (NTBG) in Hawaii has taken a lead in the conservation of this rare and unusual species by conducting manual pollination and seed collection. As a result, cultivated conservation collections have been established, which will ensure against total extinction. Recovery plans are being created that will investigate possible alternative pollinators and create guidelines for the reintroduction of the pua’ala (4). It has been suggested that a successful recovery plan needs to examine the whole of the reproductive strategy and also map the genetic diversity in the surviving populations. Research into possible pests and diseases and testing the influence of weeding and fencing has also been advocated (5).

For more information on the pua’ala, see:

• Center for Plant Conservation:
  http://www.centerforplantconservation.org/Collection/CPC_ViewProfile.asp?CPCNum=632
• National Tropical Botanical Garden (NTBG) - The Brighamia of Hawaii:
  http://www.wildlifebiz.org