58 
PACIFIC SCIENCE, VoL XXII, January 1968 
171°E); Caroline Islands (4-8°N, 49-l40°E) ; 
Philippine Islands (5-20°N, 120-127°E). 
All types will be stored at the Smithsonian 
Institution, Washington, D.C. Isotypes or syn- 
types and hundreds of glucose microslide mounts 
representing nearly every listed collection and 
some not listed in the following account will be 
stored at the University of Hawaii. 
Most of the species from the tropical Pacific 
area are small to minute. Species occurring in 
harbors and similar locations are somewhat 
larger. Those from small remote islands such as 
Johnston Island are notably smaller than those 
from larger land masses. It seems likely that 
availability of micronutrients may be a factor 
related to plant size. 
key to the species of Polysiphonia 
1. With 4 pericentral cells 2 
1. With more than 4 pericentral cells (Part II of this study) 26 
2. Main branches corticated, at least at the base P. hancockii 
2. All branches without cortication 3 
3. Rhizoids large, saccate, and prominently pigmented 4 
3. Rhizoids not pigmented 5 
4. Chiefly erect from a basal tuft of rhizoids P. rubrorhiza 
4. Chiefly prostrate, with distributed rhizoids P. saccorhiza 
5. Median parts of erect branches mostly 200p or more in diameter 6 
5. Median parts of erect branches mostly 15 Op or less in diameter 9 
6. Fruiting branches prominently narrowed at the base P. beaudettii 
6. Fruiting branches not prominently narrowed at the base 7 
7. Commonly 3-5 cm high, with branches mostly widely divaricate and with branch tips more or less di- 
chotomously branched P. hawaiiensis 
7. Mostly less than 2 cm high, branches not widely divaricate 8 
8. Segments in branch tips very short for many segments back of tapering apices; branching mostly alter- 
nate above P. sparsa 
8. Segments in branch tips otherwise; branching more or less pseudodichotomous at apices 
P. sphaerocarpa 
9. Erect branches with a trichoblast, a scar-cell or a branch at every segment except those near the 
base of a branch 10 
9. Erect branches with frequent to numerous segments without a trichoblast, a scar-cell or a branch (mostly 
on each segment in P. tenuis and P. delicatula ) 20 
10. With limited to extensive prostrate branches 11 
10. Attached by a basal tuft of rhizoids, with usually no creeping branches; plants epiphytic . . P. savatieri 
11. With prominent prostrate branches and with erect branches simple or with only a few lateral 
branches 12 
11. Chiefly erect and branched, with mostly limited prostrate branches 16 
12. With no scar-cells on prostrate branches P. tenuis 
12. With scar-cells on prostrate branches 13 
13. Scar-cells on prostrate branches divided into a group of small cells P. herpa 
13. Scar cells mostly undivided 14 
14. Erect branches 5 Op or less in diameter 15 
14. Erect branches lOOp or more in diameter P. poko 
15. Erect branches mostly less than 1 mm high, with relatively huge trichobiasts P. anomala 
15. Erect branches commonly 2 or more mm high; trichobiasts relatively small P. delicatula 
16. Branches arising apically in connection with trichobiasts 17 
16. Branches not arising in connection with trichobiasts 18 
17. Trichobiasts colorless quickly deciduous; erect branches 1-3 cm high P. flaccidissima 
17. Trichobiasts brownish, relatively persistent; erect branches 3-6 mm high P. profunda 
18. Plants mostly of sheltered and often semibrackish water, more than 3 cm high; segments of median 
parts of erect branches mostly 2 or more diameters long P. mollis 
18. Strictly marine plants of open water, less than 3 cm high; segments of median parts of erect 
branches mostly less than 1.5 diameters long 19 
19. Sublittoral plants, with branch apices abruptly acute to apiculate; tetrasporangia not protuberant 
P. apiculata 
