Herposiphonia of Tropical Pacific — Hollenberg 
537 
straight series on the side of the branches away 
from the apex of the axis bearing the branch. 
The following symbols indicate the chief col- 
lectors of the materials studied: D., Maxwell S. 
Doty, University of Hawaii; G., Malvern Gil- 
martin, Jr., at the time at the University of 
Hawaii; H., G. J. Hollenberg; Ha., H. E. 
Hackett of Duke University; H., T., and B., 
G. J. Hollenberg, Roy Tsuda, and Richard 
Buggeln; L., C. R. Long, a graduate student at 
the University of Hawaii, and T., Roy Tsuda, a 
graduate student at the time at the University of 
Hawaii, along with Richard Buggeln. All "D” 
collections were made by Maxwell S. Doty un- 
less otherwise indicated. The notation "(N.Y.)” 
indicates collections examined at the New York 
Botanical Garden. 
The areas represented in the study are mostly 
those represented in a previous report on species 
of Polysiphonia from the central and western 
tropical Pacific Ocean (Hollenberg, 1968). The 
areas are treated in the same order as in that 
report. Although they are not within the main 
areas represented by the study, it seemed best to 
include certain collections from the western 
Atlantic Ocean. Also included are collections by 
H. E. Hackett (Ha.) in the Maidive Islands 
(6°55'N to 0°4l'S, 72-73°34'E), on cruise 8 
of the TE VEGA International Indian Ocean 
Expedition, 1964. The geographic location of 
the main collection areas is given in the report 
on Polysiphonia. 
Type material will be deposited in the Smith- 
sonian Institution, Washington, D.C. Isotypes 
KEY TO THE SPECIES OF Herposiphonia 
1. Determinate branches subdistichous H. subdisticha 
1. Determinate branches not subdistichous 2 
2. Mostly with a determinate or an indeterminate branch or branch primordium on every segment 3 
2. Mostly with one or more segments between successive indeterminate branches without a branch of either 
type 11 
3. Trichoblasts and scar-cells lacking, except for scar-cells at the former point of attachment of sperma- 
tangial branches H. nuda 
3. Trichoblasts or scar-cells present, the trichoblasts sometimes very rudimentary 4 
4. Trichoblasts infrequent and very rudimentary H. dubia 
4. Trichoblasts and/or scar-cells frequent to abundant, mostly well developed 5 
5. Trichoblasts unbranched H. trichia 
5. Trichoblasts branched 6 
6. Trichoblasts and/or scar-cells not more than 2 per branchlet, strictly terminal, with a percurrent axis and 
7 or more laterals; scar-cells large H. dendroidea 
6. Trichoblasts and scar-cells otherwise 7 
7. Determinate branches composed of 40-55 segments; trichoblasts 6 or more, one per segment on the branch 
tips H. filifera 
1. Determinate branches composed mostly of fewer than 30 segments; trichoblasts mostly 2-3 at branch 
tips 8 
8. Diameter of mature determinate branches mostly 100-1 40p, with about 14 pericentral cells .... H. crassa 
8. Diameter of mature determinate branches mostly less than 80p; pericentral cells mostly 12 or fewer ... 9 
9. Procarps and spermatangial stichidia strictly terminal; trichoblasts 2-3, terminal H. parca 
9. Cystocarps and spermatangial stichidia not terminal 10 
10. Sexual reproductive structures borne 3-10 segments from the branch apex at maturity H. tenella 
10. Sexual reproductive structures borne mostly on the lower half of the determinate branch . . H. delicatula 
11. Most of the indeterminate branch primordia arrested at the few-celled stage H. obscura 
11. All indeterminate branches developing to obvious, although often small branchlets 12 
12. Most of the indeterminate branches developing into conspicuously branched laterals; main axes commonly 
growing free from the substratum in terminal parts H. arcuata 
12. Most of the indeterminate branches remaining rudimentary or small 13 
13. Central cells of determinate branches conspicuously larger than the pericentral cells 14 
13. Central cells of determinate branches not conspicuously larger than the pericentral cells 15 
14. Determinate branches mostly less than 1 mm high and composed of fewer than 30 segments . . H. variabilis 
1 4. Determinate branches commonly 10-15 mm high and composed of 5 0-70- (90) segments . . . H. pacifica 
15. Determinate branches mostly 3 5-5 Op in diameter, composed of 12-14 segments; procarps and sperma- 
tangial stichidia arising mostly on the basal half of the determinate branches H. delicatula 
15. Determinate branches mostly 60-lQ0p in diameter, composed of 16-1 8- (30) segments; procarps and 
spermatangial stichidia arising terminally or in the upper half of the branches; spermatangial stichidia 
with a short sterile tip H. tenella form secunda 
