ECOLOGY AND TAXONOMY OF Halimeda 91 



Section Halimeda [cont.) Section Micronesicae 



H. macrophysa H. micronesica 



H. discoidea H. fragilis 



H. taenicola H. melanesica 



H. hikinensis 

 H. gracilis 



E. Key to Atlantic species, and list of Atlantic species 



1. Key to Atlantic species 



1. Plants growing in sand or other loose substrate; holdfast usually- 

 well developed, rarely less than 1 cm long and frequently massive; 

 nodal medullary filaments uniting into a single group, the adjacent 

 filaments usually communicating by pores . . . section Rhipsalis . . 2 



1. Plants generally attached to rock or if associated with sand 

 lacking a well-developed bulbous holdfast; holdfast rarely 

 exceeding 1 cm in length, although sometimes it may spread 

 laterally to this size or somewhat larger; more than one holdfast 

 region may be present; nodal medullary filaments remaining 

 separate or uniting in twos, threes and occasionally fours . . 5 



2. Segment surface appearing pitted when viewed macroscopically ; 

 peripheral utricles generally exceeding 110 [jim in surface 

 diameter . . . . . . . . . . . . H. favulosa, p. 96 



2. Segment surface not appearing pitted when viewed macroscopic- 

 ally; peripheral utricles generally less than 100 pim in surface 

 diameter . . . . . . . . . . . . . . . . 3 



3. Segments of the upper half of the plant, except those supporting 

 branches, predominantly cylindrical, their length usually at least 

 three to four times their diameter . . . . . . H. monile, p. 98 



3. Segments of the upper half of the plant flat, or if cylindrical the 

 length usually not more than twice their diameter . . , . 4 



4. Peripheral utricles generally 50 [xm or less in surface diameter; 

 segments predominantly subcuneate to reniform with outer 

 margin entire to shallowly lobed ; basal portion of plant commonly 

 of two to three cylindrical to subcuneate or at times reniform seg- 

 ments, the upper one supporting several subcuneate segments 

 often in an imbricated arrangement; plants to 10 cm tall 



H. simulans, p. 103 

 4. Peripheral utricles generally exceeding 50 pim in surface diameter ; 

 segments cylindrical to cuneate to discoidal and reniform with the 

 outer margin often deeply lobed ; plants to 24 cm tall 



H. incrassata, p. 93 



