NOTES 
Distribution of the Algal Genera Rhipilia and Sargassum 
in the Central Pacific 
In assembling marine algal floristic infor- 
mation on the Central Pacific, certain peculi- 
arities have come to light. One of these is an 
apparent exclusiveness of range between the 
genera Rhipilia and Sargassum. 
Classman (Amer. Midland Nat. 48: 735-740, 
1952) reports two species of Sargassum from 
Ponape. He found no Rhipilia. Neither genus 
has been found in available collections from 
Wake Island or Guam. Taylor (Plants of 
Bikini, pp. 70-73, 1950) reports Rhipilia 
from the four northern Marshall atolls he 
studied — Eniwetok, Rongelap, Bikini, and 
Rongerik. Despite a thorough study he did 
not find Sargassum. Rhipilia geppii Taylor but 
not Sargassum is present in collections from 
Arno Atoll (southern Marshalls) and Butari- 
tari ( northern Gilberts ) . 
Of the two genera, Sargassum is abundant 
in the Hawaiian archipelago. Rhipilia seems 
to be absent. Neither genus has been found 
during recent collecting at Johnston Island. In 
collections seen from Palmyra (Line Islands), 
Rhipilia geppii has appeared but not Sargassum. 
Howe and Lyon (Hawaii Col. Pubs., Bui. 4: 
31-32, 1916) reported neither genus in their 
brief discussion of the algae of Palmyra. Sar- 
gassum is absent, likewise, in collections at 
hand from Canton Island in the Phoenix 
Group. Setchell (Carnegie Inst. Wash., Pub. 
341, parts 1, 3, 1924) found two species of 
Sargassum at Tutuila in American Samoa, no 
Rhipilia; and at Rose Atoll, neither genus. 
No Sargassum was found in collecting at 
.Aitutaki in the Cook Islands; however, rela- 
tively no more than a glimpse of the reef and 
lagoon was had. No Sargassum, nor even 
Turbinaria, was seen on four northern Tuamo- 
tuan atolls visited, although intensive search 
was made at Takume and Raroia, where 
Rhipilia geppii was found in abundance. At 
Tahiti, Setchell (Calif. Univ., Pubs. Bot. 12: 
61-142, 1926) distinguished four species of 
Sargassum (and the genus is indeed conspi- 
cuous there) but not Rhipilia. 
Setchell reports an alga, Avrainvillea lacerata 
(Harv. ) J. Ag., as occurring at Tahiti "in 
extended patches in deep shaded holes in 
basalt rocks, upper littoral zone” and elsewhere 
there. This does not sound like the ecology 
of Rhipilia geppii. To be sure, Taylor after 
studying this material notes that this species 
though suggestive is distinct from his Rhipilia 
geppii. He notes, too, that this Avrainvillea 
occurs at Washington Island (Line Islands), 
in the northern Marshalls, and in Java. This 
genus is considered to be a close relative of 
Rhipilia. 
The islands which apparently lack Sargassum 
are not without algae of world-wide pantropic 
or Indo-Pacific distribution. As an example. 
Palmyra has yielded Asterocytis ornata (C. Ag.) 
Hamel, a world-wide species (at least pole- 
ward through temperate waters ) ; pantropic 
elements such as Bryopsis pennata Lam.; and 
Indo-Pacific elements such as Goniolithon 
frutescens and Caulerpa serrulata. Similar 
evidence for other islands where Rhipilia is 
present and Sargassum absent militates against 
describing the border between this apparent 
distribution of the two genera as a division 
between zones. A more likely hypothesis is 
that there is a gradual biotic change as this 
area is passed through and that the large dis- 
367 
