The vegetation 
The natural vegetation of Christmas Island is characteried by 
xeric and semi-xeric Pacific strand species such as Portulaca lutea, 
Heliotropium anomalum , Scaevola and Tournefortia . (Christophersen, 1927). 
These herbs and shrubs along with Sida , Suriana, Hedyotis and Lepturus 
form distinct associations which at one time covered the atoll, the 
largest in land area found in the world. The island appears to have 
been created from a group of smaller islets which were united by storm 
and wave deposited debris and, possibly, uplift. (Rougier, 1914). 
These old islets forms the upland areas of the island which are covered 
with a Scaevola - Tournefortia association mixed with open areas of Sida 
and Lepturus . A banded type of association arrangement is found around 
the shores of the inner lagoon and lagoon flats where a Suriana-Hedyotis 
association is common above the periodically flooded areas. An under¬ 
growth of Sida , Lepturus and Portulaca is common in open areas between 
the edge of the lagoon and the Scaevola scrub. Sesuvium forms associa¬ 
tions with Eragrostis whitneyi and Heliotropium at the lagoon edge or on 
the raised islets of the lagoon area. Often Sesuvium forms pure stands 
in these areas. In 1965 a Cuscuta sp. was discovered on one islet in 
the heavily dissected area of the lagoon in the middle portion of the 
island. A number of islets were inspected but no other lovale was found 
for this undetermined species. Lepidium bidentatum occurs in dry open 
areas near the lagoon on the SW end of the island. 
The three islets of the Christmas atoll are interesting in that 
some but not all of the species found on the larger island are represented 
in a relatively small area. Cook Island is sparsely covered, in some 
places just at the periphery, with the Scaevola - Tournefortia association. 
Heliotropium and Portulaca are found on the dry open portions with Lepturu s 
and Sida forming a relatively thick cover on the S end of the island. 
Cassytha is found on the Boerhavia , Scaevola , Portulaca and Sida . The soils 
are made up of sand and coral rubble. The two smaller islets of Motu Upua 
and Motu Tabu are sand islets with Scaevola - Tournefortia scrub. On 
Motu Tabu a Pisonia tree to 5 m. is found in the center of the island and 
several small Hedyotis shrubs were found on ; the E Shore just above the high 
tide line on the sand and gravel beach. Seedlings of Tournefortia , Scaevola 
and Eragrostis whitneyi were found in pioneer areas of newly deposited sand 
on the E side of Motu Tabu and Motu Upua . Tribulus cistoides and Boerhavi a 
repens are found on all three islets sometimes forming thick mats of over¬ 
lapping stems. These species often form a considerable litter. 
The S area of the island was surveyed in 1965 . Of special interest 
was the ground zero area of the 1957 bomb test site and adjacent areas 
to the north of the site. The vegetation in the S area consists at pre¬ 
sent of Lepturus - Sida stands with Portulaca and Boerhavia . Tribulus is 
found in patches. This vegetation type approximates that which was present 
before the tests. The Scaevola - Tournefortia cover on the S part was 
almost completely eliminated. In 1965 the dead remains of large Tournefortia 
trees were to be seen. Scaevola scrub appeared to be recovering by sprout¬ 
ing from the base. Some of these were 1.5 -2.5m. high. New plants probably 
from seedling were evident along the south shore. Nesting bluefaced boobies 
and sooty terns were present in these open areas in large numbers. 
