Olulu  (Brighamia insignis)

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 (4).

The Latin ‘insignis’ means ‘remarkable’, which is a particularly apt epithet for this plant, long considered one of the most unusual and interesting plants of the Hawaiian flora (5). This member of the perennial bellflower family (Campanulaceae) is one of two morphologically similar species in the genus Brighamia, B. insignis and B. rockii (3). ‘Olulu possesses a thick, succulent stem that is swollen at the base, tapers towards the apex, and is crowned by a dense rosette of fleshy leaves (3) (6). These plants are usually single-stemmed, although individuals have been observed with as many as four heads (7). Flowers are cream to yellow in colour and salverform (trumpet shaped) (7). Clustered into groups of three to eight (3), the ‘olulu flowers possess a fragrance that resembles mild honeysuckle (5).

Both Brighamia species are endemic to Hawaii (3). Once common on the four highest islands of Hawaii, it is thought that only approximately seven mature individuals of ‘olulu now survive across two subpopulations on the Island of Kaua’i, making this species one of the rarest in the world (2) (8).

This specialised plant is found in areas with little soil, from sea level to 480m elevation on the rocky ledges of Hawaii’s volcanic basalt sea-cliffs (3) (7). They are also found in lowland dry grasslands or scrublands with annual rainfall usually less than 170 cm/year (3).

A long-lived perennial, ‘olulu is a succulent plant adapted to growing in the salty environments of sea cliffs (6). Flowers bloom in September and October, and the small green capsule fruit ripens six to eight weeks after pollination (5). Scientists believe that moths have historically been the natural pollinator of Brighamia flowers, a hypothesis supported by the fact that the nectar of ‘olulu is sucrose-dominated and characteristic of flowers pollinated by hawk moths (Lepidoptera sphingidae) (7). The disappearance of this natural pollinator has potentially been a significant contributor to the decline in number of ‘olulu plants found in the wild (7).

Primary explanations offered for the decline of the ‘olulu include competition from introduced invasive plants (3), loss of its natural pollinators (7), and destruction by naturally occurring stochastic events such as land slides or hurricanes (6). Hurricane-force winds have recently scoured the Na Pali sea cliffs, killing many plants (7). Additionally, while most populations are found on virtually inaccessibly sea-cliffs, the Waiahuakua population on Kaua’i is more accessible and has suffered damage from the activities of feral goats (6). In the early 1990s Kaua’i had a total of approximately 150 individuals on the Na Pali sea cliffs where today there remain only seven (7). With such critically low numbers there is a concern that genetic variability will get too low, as a result of inbreeding between remaining plants, for the species to adequately respond to environmental pressures (7) (3). Thus, although once fairly common, this species is now teetering on the brink of extinction in the wild (8).

Botanists and horticulturists concerned about the plight of Hawaii’s threatened plant species have helped save this fantastic plant from total extinction by pollinating the remaining wild specimens by hand and collecting seeds for propagation (8). Successful germination of the seeds has enabled large numbers of plants to be grown in botanical gardens to be used in a replanting programme (8). Today there are more plants in the Limahuli Gardens and McBride Gardens on Kaua’i than there are in the wild (5)! Endangered species may benefit from increased artificial gene flow, especially if they have passed through a genetic bottleneck due to inbreeding depression, and hand pollination experiments have aided in this respect (7). Investigation into possible alternative pollinators is also being planned (7). Such research will undoubtedly aid the creation of guidelines for the re-introduction of the magnificent ‘olulu into protected cliff sites where it once flourished (7).

For more information on the olulu, see:

• Center for Plant Conservation:
  http://www.centerforplantconservation.org/Collection/CPC_ViewProfile.asp?CPCNum=630
• National Tropical Botanical Garden (NTBG):
  http://www.ntbg.org/plants/