An Account of the Species of the Red Alga Herposiphonia Occurring in the 
Central and Western Tropical Pacific Ocean 
George J. Hollenberg 1 
ABSTRACT : Fourteen species of the genus Herposiphonia are described. The fol- 
lowing species and varieties are new: H. arcuata, H. crassa, H. delicatula, H. den- 
droidea , H. dendroidea var. minor, H. dubia, H. nuda, H. obscura, H. parca var. 
interrupta, H. pacifica, H. trichia, H. variabilis. The distributional range is extended 
for H. parca, H. subdisticha, and H. tenella. H. secunda is reduced to a form of 
H. tenella. 
Emphasis is given to the nature and arrangement of trichoblasts and of sexual 
reproductive structures as features of taxonomic importance. 
The genus Herposiphonia was established by 
Nageli (1846). H. tenella is generally con- 
sidered the type species, although no binomials 
are cited by Nageli. The name Herposiphonia 
was also used by Kuetzing (1843:417) for a 
group of species of Polysiphonia, including P. 
tenella ( Hutchinsia tenella of C. Agardh 1828: 
105). Hence, Herposiphonia (Kuetzing) Na- 
geli appears to be the basis for lectotypification 
of the genus by Schmitz (1889), with H. tenella 
as the type species. 
The basic features of the genus have been 
described in considerable detail by Falkenberg 
(1901) and by Boergesen (1918). Approxi- 
mately 30 species have been previously described. 
The most distinctive features of the genus are 
the dorsiventral construction and the more or 
less regular sequence of exogenous determinate 
branches and indeterminate branches. In the 
basic pattern of branching, indeterminate 
branches arise on alternate sides of the axes at 
intervals of four nodes, with determinate 
branches alternating on either flank at the inter- 
vening nodes, and with the most distal determi- 
nate branch on the same side as the next in- 
determinate branch distally. In most species the 
indeterminate branches usually remain small or 
rudimentary. The determinate branches are 
simple in most species, but are branched in a 
few species. The apex of indeterminate branches 
is usually inrolled away from the substratum, 
the determinate branches commonly arching 
1 University of Redlands, Redlands, California. 
Manuscript received September 26, 1967. 
toward the apex of the related indeterminate 
branch. The branches are never corticated. In 
certain species the chromatophores are com- 
monly arranged in transverse bands in the peri- 
central cells on the side toward the central cell. 
Rhizoids always arise from the distal end of 
ventral pericentral cells, most commonly one per 
segment. They are cut off from the pericentral 
cell by a curving wall. 
Trichoblasts and reproductive structures arise 
exclusively on the determinate branches. The 
sequence of determinate and indeterminate 
branches, commonly considered a dependable 
taxonomic feature, seems to be reliable for most 
species, but not for certain species. The relative 
number and nature of the trichoblasts, and the 
number of segments in determinate branches, as 
well as the number of pericentral cells, are 
features usually characteristic for a given species, 
although there is often considerable variation, 
especially in the number of segments in the 
determinate branches and the degree of develop- 
ment of the trichoblasts. The nature and posi- 
tion of fully mature trichoblasts is, in the opin- 
ion of the writer, a fairly dependable taxonomic 
feature. Also, the number of segments develop- 
ing in determinate branches beyond the first 
formed trichoblast is usually significant. 
Probably one of the most important taxo- 
nomic features is the nature and position of the 
reproductive structures, especially the sexual 
reproductive structures, although, unfortunately, 
the latter are infrequently found. Tetrasporangia 
always arise one per segment in normally 
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