314 
PACIFIC SCIENCE, Vol. XIV, October I960 
LOCATION AND TOPOGRAPHY 
Eniwetok Atoll is found near the northern 
end of the double chain of atolls forming the 
Marshall Islands. It is at 11° 30' N., 162° 14' E. 
Its shape is a broad ellipse, running NW to SE, 
Its length is 22 nautical mi. The reef is well 
developed and nearly continuous, but with sev- 
eral deep passages from the sea to the lagoon. 
The islets total 39, and nearly all of them and 
all the large ones lie on the northeastern or 
windward side. The largest islets are Eniwetok, 
Parry, Engebi, and Runit. Eniwetok, the largest, 
is 2V4 nautical mi. in length. 
SIZE OF THE FLORA 
Eniwetok is in the northern and drier section 
of the Marshall Islands. As a consequence it 
does not have, and probably never had, dense, 
lush, damp forests, nor is its total flora large. 
Its indigenous flora totals 42 species or minor 
taxa, of which 4 are endemic, all of these four 
being in the genus Pandanus. The total of ad- 
ventive weeds is 27, and that of cultivated 
plants, including both food crops and ornamen- 
tals is 26. Species known only by drifted seeds 
on the beaches total 7. All together the living 
flora totals 95 species or minor taxa. 
Seeds or fruits found in the jetsam on the sea 
and lagoon beaches add an element in the flora. 
Many come from species growing on the islets 
of the atoll, but there are others from species 
unknown on the island and certainly floated on 
the sea currents or waves from distant regions. 
Of these Hernandia sonora is the only one that 
is native to other islands of the Marshall group, 
ones to the south in the wetter belt. Two spe- 
cies, Caesalpinia Bonduc and Aleurites moluc- 
cana, are of wide occurrence and could have 
come from the northeast, south, or west. These 
are both abundant in Hawaii. Two species, 
Mucuna urens and Sapindus Saponaria, must 
have come from the northeast, being abundant 
in Hawaii and absent in other parts of the tropi- 
cal Pacific. Two species, Dioclea reflexa and 
Entada phaseoloides, must have come from the 
south or west. In sum, of the 6 drift species, 4 
certainly floated from Hawaii on the Japan Cur- 
rent which regularly flows past Hawaii towards 
the Marshalls and the central Pacific. The two 
species of southern or western origin may have 
travelled eastward on the Equatorial Counter 
Current and have been wafted northward dur- 
ing a southerly storm. 
ECOLOGY 
Details of the terrestrial plant ecology were 
reported to the Atomic Energy Commission in 
1950- They were for publication in UWFL-24. 
Because of the dryness and the small, mostly 
narrow, islets, there is little diversity in the 
habitats. There are no good sand dunes, or fresh 
ponds, or central hollows with rich, black humus 
top soil. The only habitats are: outer beaches of 
coral rock or coral gravel, inner beaches of coral 
sand, small coral sand dunes, coral gravel flats, 
and coral sand flats. Some of the plants seem 
restricted to a particular habitat, but the zones 
formed are rather indefinite. Their occurrence 
seems governed not so much by the soil, as by 
the size of the islet and the distance from the 
sea which seems to determine the shelter from 
salt spray, and the availability of fresh water 
in the water table. Since the habitat differences 
are slight, they have, for the sake of brevity, 
been omitted in the descriptive flora which fol- 
lows, except when special and very local. In 
this flora every known collection is briefly cited 
with its islet, date of collection, and collector’s 
name and the number. From this, future re- 
search workers can learn the former occurrence 
of each species, and the date for each record. 
This chronological information is of value, since 
it appears that each atomic bomb explosion has 
restricted, or may restrict, the occurrence of, or 
exterminate some members of, the flora. 
ACKNOWLEDGMENTS 
The author’s sincere thanks are due Dr. 
Lauren R. Donaldson of the Radiation Biological 
Laboratory, University of Washington, Seattle 
5, Washington, and Dr. Leonard D. Tuthill, 
then dean of the Graduate School, University of 
Hawaii, Honolulu 14, Hawaii, for making pos- 
sible the writer’s two explorations of Eniwetok. 
