56 
PACIFIC SCIENCE, Vol. V, January, 1951 
dignify them with Latin names. For con- 
venience they are listed by number, each 
under the island where it occurs. 
DISTRIBUTION 
So far species of Myoporum have not been 
discovered on any of the islands occurring 
in the 3,000-mile expanse of sea between 
Hawaii and the Austral Islands. It is not 
surprising that they are missing from low coral 
atolls such as Palmyra and Fanning, but their 
absence from the Society Islands, the Mar- 
quesas, and Makatea is unexpected, as is their 
absence from other large Pacific islands such 
as Samoa and Fiji. 
The disjunct distribution of M. sandwi- 
cense — with two subspecies in the Hawaiian 
Islands and one in the Cook Islands (Man- 
gaia) — is not unique, however. For instance, 
Isachne distichophylla has been found only on 
Rarotonga and in the Hawaiian Islands. 
Hedy Otis section Bikkiocarpa has two species, 
one from West Maui and one from Rapa (see 
Fosberg, 1943: 25). The genus Phyllostegia 
has 23 species in the Hawaiian Islands and 
one in Tahiti. Our present state of knowledge 
is insufficient to explain these facts of dis- 
tribution. However, the theory of Zimmer- 
man (1948: 49-52) that high volcanic islands, 
now reduced to reefs or atolls by erosion, 
once existed as stepping-stones in the mid- 
Pacific indicates how these cases of bicentric 
distribution might have arisen. 
At the time of Captain Cook’s visit 
Myoporum undoubtedly existed on all seven 
of the main Hawaiian Islands. It is now absent 
from the denuded island of Kahoolawe, but 
Forbes (1913: 86) learned from old visitors 
to the island that the naio had been seen there 
before the dry forest was wiped out. The 
relative abundance of the species at those 
localities where it still persists has no doubt 
undergone great changes. In some areas, as 
at Kaena Point on Oahu and the Puuwaawaa 
district of Hawaii, it may be as common as it 
was before the dry forests were disturbed; 
on the other hand it is rare or absent from 
areas such as the Lualualei region on Oahu, 
western Molokai, and the Kohala peninsula 
of Hawaii, where probably it was once very 
abundant. 
In the Austral Islands the destruction of 
the native forests has been so complete that 
a clear picture of the distribution of Myo- 
porum there may never be obtained. St. John 
tells me that he made a special effort to col- 
lect Myoporum on these islands during the 
Mangarevan Expedition of 1934 and that 
few plants of the genus could have been 
overlooked in the vestiges of the native for- 
est. Judging from his findings, M. rapense 
var. Skottsbergii and the form described by 
Brown as M. rimatarense may well be extinct. 
On the basis of our present knowledge, 
however, it seems significant that M. rapense 
is found on the three lower islands of the 
Austral group and that its derivative M. 
Stokesii is restricted to Raivavae. 
One of the chief difficulties in under- 
standing the distributional pattern of Poly- 
nesian Myoporum is that the means of long- 
range dispersal of the genus are still a matter 
of conjecture. It does not appear likely that 
the fruits are spread by ocean currents, since 
my own observations show that they will 
float for no more than a few days. Dispersal 
by birds is a possibility, since some endemic 
Hawaiian birds were known to have eaten 
the seeds; but there is no evidence that any 
migratory birds are fond of the fruits. It must 
be admitted that the dispersal mechanism of 
Myoporum still remains unknown, and that 
the accidental transport by hurricanes is as 
likely a possibility as any. 
RELATIONSHIPS OF THE SPECIES 
At present, and in spite of a fairly recent 
monograph (Kraenzlin, 1929), the genus 
Myoporum is in great need of critical revision. 
The seat of the greatest systematic difficulty 
is the complex of chiefly insular species which 
includes the three Polynesian species. Almost 
nowhere within this insular complex are the 
species well defined, and it is very difficult to 
