ECOLOGY AND TAXONOMY OF Holimeda 87 



4. Fan-shaped basal or suprabasal segment present ; plant heavy-set 

 and somewhat squat with predominantly broad, reniform or ovate 

 segments with crenulated margins, to 12 mm long, 17 mm broad 



H. borneensis, p. 105 



4. Fan-shaped basal or suprabasal segment absent; basal portion of 

 plant of two to three cylindrical to subcuneate or at times 

 reniform segments, the upper one supporting several subcuneate 

 segments which are often arranged in an imbricated fashion, or 

 sometimes a stalk region present which has developed from the 

 fusion of small adjacent segments; segments to 11 mm long, 15 mm 

 broad, margins sometimes shallowly trilobed or undulating but 

 usually not crenulated . . . . . . . . H. simulans, p. 103 



5. Segment surface appearing pitted when viewed macroscopically ; 

 peripheral utricles generally exceeding 110 [j.m in surface 

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



5. Segment surface not appearing pitted when viewed macroscopic- 

 ally ; peripheral utricles generally less than 100 [im. in surface 

 diameter . . . . . . . . . . . . . . . . 6 



6. 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 . . . . . . . . . . 7 



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

 length usually not more than twice their diameter . . . . . . 8 



7. Diameter of the cylindrical segments remaining fairly constant 

 from base to apex of the plant and averaging 1-0-1 -5 mm; stalk 

 of thallus short, of one to two segments; plant of Atlantic 

 distribution H. monile, p. 98 



7, Diameter of the cylindrical segments decreasing from base to apex 

 of the plant, averaging 3-4 mm near the base, and 1-0-1 -5 mm 

 towards the apex ; caulescent, or in older plants a number of these 

 cauline structures may be consolidated laterally into a basal fan- 

 shaped structure; of Indo-Pacific distribution H. cylindracea, p. 100 



8. Plants thick- set in appearance, the segments averaging 2 mm in 

 thickness; segments subcuneate to cylindrical, often becoming 

 subspherical towards the plant apex . . . . H. stuposa, p. 101 



8. Plants not appearing thick-set, segments (excluding the basal 

 ones) averaging 0-75-1-00 mm in thickness; segments generally 

 subcuneate to reniform . . . . . . • • • • • • 9 



9. Peripheral utricles generally 50 y.m 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 

 segments, the upper one supporting several subcuneate segments 

 often in an imbricated arrangement; plants to 10 cm tall . . 



H. simulans, p. 103 



