114 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL.12 



Halidrys dioica Gardner 



Setchell & Gardner 1925, p. 707. 



Mexico: Baja California, on littoral rocks at South Bay, I. Cerros, 



no. 34-632, 10 Mar. 1934. 



SARGASSUM C. Agardh, 1821 



Plants of moderate to large size, with distinct often massive lobed 

 holdfasts and well-diflferentiated branches with broad to filiform, occasion- 

 ally forked, entire or serrate leaf organs ; lateral stalked vesicles usually 

 present; receptacles axillary or paniculate, more or less forked, cylindrical, 

 nodulose, sometimes flattened or serrate; eventually bearing eggs singly 

 in the megasporangia. 



KEY TO SPECIES 



1. Leaves or their divisions narrowly linear, in general 10 times as 

 long as broad, or more 2 



1. Leaves in general less than 10 times as long as broad ... 5 



2. Leaves without evident costa, linear to generally filiform, forked, 

 without cryptostomata ^ 



2. Leaves with generally evident costa, more or less linear . . 4 



3, Plant generally loose in habit; the inflorescences moderately to 

 markedly loose S. setifolium 



3. Plant pyramidal, of close habit ; inflorescences congested . . . 

 S. galapagense 



4. Leaves generally forked, more slender, less dentate ; inflorescences 

 moderately loose S. Templetonil 



4. Leaves simple or in the upper parts of the plant somewhat forked, 

 dentate ; inflorescence compact S. zacae 



5. Leaves entire or slightly erose, cryptostomata absent; vesicle 

 stalks often alate S. albemarlense 



5. Leaves subentire to strongly serrate 6 



6. Vesicles absent ; leaves oblong lanceolate, subentire or moderately 

 serrate with small teeth, particularly the basal leaves . S. Howellii 



6. Vesicles generally present; leaves conspicuously, often coarsely 

 serrate 7 



7. Leaves of small to moderate size 8 



7. Leaves conspicuously large and thin, coarsely serrate ... 12 



8. Receptacles dentate S. Liebmannii 



8. Receptacles smooth to rough, but not dentate 9 



