Notes on Status and Ecology of the Endangered Hawaiian Annual 'Awiwi, Centaurium sebaeoides (Gentianaceae) 1

The annual, endemic, coastal herb Centaurium sebaeoides is the only native Hawaiian species in the gentian family. The U.S. Fish and Wildlife Service listed it as Endangered under the Endangered Species Act on 29 Octo­ ber 1991. Before surveys reported here, the total population of this species statewide was estimated at 80-110 individuals in eight populations. During counts made in April and May 1997, following ample winter rains, 12 popula­ tions of C. sebaeoides with a total of 6300-6600 plants were noted on five islands (Kaua'i, O'ahu, Lana'i, Moloka'i, and Maui). Five populations were mapped with a global positioning system and counted; in the remaining seven populations, the numbers of individuals were estimated. More recent surveys in 1998-1999 estimated a total of only 60-80 individuals at all sites. Such dra­ matic population fluctuations are believed to be related to the sporadic occur­ rence of winter rains. Threats that further contribute to the rarity of the species include (1) displacement and overtopping by salt-tolerant nonnative woody spe­ cies, especially Casuarina spp., (2) trampling and erosion of habitat by ungu­ lates, and (3) damage caused by off-road vehicles. Centaurium sebaeoides (Griseb.) Druce is the only native Hawaiian gentian (Gentiana­ ceae). The genus Centaurium consists of about 20 species distributed in North Amer­ ica, Eurasia, mountains of South America, northern Africa, Australia, and some Pacific islands (Wagner et al. 1990). Though Hille­ brand (1888) noted that the Hawaiian spe­ cies was similar to a Mediterranean species, Erythraea spicata, Fosberg (1948) listed the progenitor species as likely having originated in the New World. Another species of the genus, bitter herb (Centaurium erythraea Raf.), native to Eurasia, is naturalized and relatively common on all of the main Ha­ waiian Islands except Ni'ihau at 10-2140 m elevation (Wagner et al. 1990). The native Hawaiian name of C. sebaeoides is 'awiwi (Pukui and Elbert 1986).