An Account of the Species of Polysiphonia of the Central and 
Western Tropical Pacific Ocean 
I. Oligosiphonia 1 
George J. Hollenberg 2 
ABSTRACT : Twenty-four tetrasiphonous species are described. The following spe- 
cies or varieties are new: Polysiphonia anomala, P. apiculata, P. delicatula , P. flac - 
cidissima var. decimera, P. flaccidissima var. iki, P. flaccidissima var. lopi , P. ha - 
waiiensis, P. herpa, P. poko, P. poko var. longii, P. profunda, P. pseudovillum, 
P. quadrata, P. ruhrorhiza, P. setacea, P. sphaerocarpa var. distans, P. sphaerocarpa 
var. filifera, P. subtilissima var. abbottae, P. tenuis, P. tuberosa, P. scopulorum var. 
macrotrichia, P. scopulorum var. minima. The following new combinations are 
made: P. saccorhiza (Collins and Hervey) comb, nov., P. sparsa (Setchell) comb, 
nov., P. scopidorum var. villum (J. G. Agardh) comb, nov., P. mollis var. tonga - 
tensis (Harvey) comb. nov. 
This paper includes the results of studies made 
in 1962 of Dr. Maxwell Doty’s collection of 
marine algae at the University of Hawaii, and 
of collections made by the author during 1948 
in the Marshall Islands and in 1964-1965 of 
collections by Doty from widely scattered islands 
of the central and western tropical Pacific Ocean. 
The taxonomically important features of the 
genus Polysiphonia, such as the number of peri- 
central cells, cortication, the nature and arrange- 
ment of trichoblasts, the origin of branches in 
relation to trichoblasts, and the nature of the 
spermatangial branches were pointed out in pre- 
vious papers (Hollenberg, 1942^, 1942^, 1944, 
1961) and still earlier by Falkenberg (1901) 
and others. Also it was previously recognized 
that the connection between the rhizoids and the 
pericentral cells bearing them is a feature of 
dependable taxonomic value. Not sufficiently 
recognized in earlier work on the genus is the 
nature of the apex of the rhizoids. In general 
the writer’s observations indicate that the length 
and abundance of rhizoids and whether or not 
the tip is digitate is a variable feature for a 
given species, dependent largely on the nature 
1 Species with five or more pericentral cells will 
be treated in a later paper. This study was made pos- 
sible through the support of research grant No. GB- 
2735 of the National Science Foundation. 
2 University of Redlands, Redlands, California. 
Manuscript received January 17, 1967. 
of the substratum and to some extent on the 
proximity of other plants or branches of the 
same plant. The degree of development of 
trichoblasts and their persistence is likewise a 
variable feature in most species. 
On the other hand the development of multi- 
cellular rhizoids, by cutting off a series of cells 
from the apex, seems to be a more constant 
feature of considerable taxonomic importance. 
Although in some species gradations may occur, 
in general in mature rhizoids the apex is either 
clearly multicellular or simple to merely digitate 
in a given species when in contact with a firm 
substratum. Also the point of origin of rhizoids 
is characteristic for certain species. It was pre- 
viously pointed out (Taylor, 1945:302) that 
the rhizoids arise mostly on the distal end of 
the pericentral cells (nearest the branch tip) in 
P. howei, as they seem to do in all species of 
Herposiphonia, whereas in most species of Poly- 
siphonia they arise on the proximal end or from 
the center of the pericentral cell. 
Three species, P. scopulorum, P. sparsa, and 
P. saccorhiza, formerly considered as species of 
Lophosiphonia are included in this paper. In a 
former paper (Hollenberg, 1942^) it was con- 
cluded best to follow Setchell and Gardner 
(1903) in placing P. villum J. G. Agardh in 
the genus Lophosiphonia even though in a num- 
ber of species of Polysiphonia, which are not 
chiefly prostrate in habit, erect branches com- 
56 
