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PACIFIC SCIENCE, Vol. VIII, October, 1954 
GREEN ALGAE 
Key to the Genera of Chlorophyta 
1. Thallus calcified 2 
Thallus uncalcified 5 
2. Plant body or axis cylindrical 3 
Plant body or segments flattened 4 
3. Thallus simple, cylindrical. . .Neomeris 
Thallus with cylindrical axis bearing one 
or more verticils Acetabularia 
4. Thallus flabellate, not segmented 
Udotea 
Thallus consisting of flat segments .... 
Halimeda 
5. Thallus simple, essentially one-celled. .6 
Thallus multicellular, or of branched, 
coenocytic filaments 8 
6. Thallus attached by a penetrating peg. . 
Halicystis 
Thallus attached by rhizoids 7 
7. Thallus more or less spherical, the small 
rhizoids cut off by a septum from the 
main cell Valonia ventricosa 
Thallus elongate, clavate, the rhizoids 
branched, nonseptate Boergesenia 
8. Thallus filamentous and branched, or 
composed of branched, septate or coe- 
nocytic filaments 14 
Thallus cellular, not filamentous or com- 
posed of obvious filaments 9 
Thallus filamentous, unbranched, uni- 
seriate Chaetomorpha 
9. Thallus composed of large cells 1 mm. 
in diameter or more 10 
Thallus composed of small cells .... 1 1 
10. Thallus hemispherical, solid or hollow, 
the cells compact Dictyosphaeria 
Thallus irregular, of non-compacted, 
coarse, clavate cells 
Valonia aegagropila 
11. Thallus subspherical or clavate 
Bornetella 
Thallus not subspherical or clavate, com- 
posed of expanded, or hollow, cellular 
membranes 12 
12. Thallus parts hollow, tubular 
Enteromorpha 
Thallus parts expanded, membranous 1 3 
13. Cells in two layers, irregularly disposed 
Ulva 
Cells in one layer, radially disposed in 
flabellate blades Anadyomene 
14. Filaments cellular, or at least frequently 
septate 23 
Filaments non-septate or infrequently sep- 
tate 15 
15. Filaments dichotomously branched. . 16 
Filaments not dichotomously branched 
19 
16. Filaments growing together to form a 
large, spongy, flabellate plant body 
Avrainvillea 
Filaments free, not forming a flabellate 
plant body 17 
17. Filaments prominently constricted just 
above the dichotomies . . Chlorodesmis 
Filaments not constricted at the dicho- 
tomies 18 
18. Filaments attenuated from 40-50 jj, below 
to 10-12 iJL in ultimate segments 
Derbesia 
Filaments increasing in diameter from 
60-80 IJL near the base to 125 m above. . . 
Pseudochlorodesmis 
