ECOLOGY AND TAXONOMY OF Holimeda 27 



filaments fuse completely in groups of twos or threes and do 

 not separate thereafter, although the filaments eventually 

 branch in the segment above that particular node. 



The first type was originally described by Askenasy (1888) and is 

 represented by the species incrassata. The second type, represented by 

 opuntia, and the third by tuna and gracilis were first delimited by 

 Barton. 



The usefulness of Barton's monograph at that particular time was 

 strengthened further by her rigid application of this nodal character. 

 Her taxonomy was supplemented with one other microscopical 

 character, the extent of adhesion of the peripheral utricles and by 

 judicial use of segment shape. As a result, specimens with similar 

 nodal anatomy, such as incrassata and tridens, were assigned the same 

 epithet instead of different ones which had happened when the 

 taxonomy was based on segment morphology. Ellis and Solander (1786), 

 and subsequently others, including Agardh (1 887), had considered them 

 distinct species on the basis of the predominant segment shape being 

 plano-convex in incrassata and tridentate in tridens. 



A prime result of Barton's treatment was the retention of but 7 

 species of Halimeda (Table I) out of the more than 25 that had been 

 recognized hitherto. A second result was that order within the genus 

 was established. 



A few specimens, however, were obviously troublesome to Barton, 

 for they did not fit her scheme. Of these, a few are best interpreted as 

 being poorly developed individuals. A very few were aberrant in that 

 the medullary filaments did not fuse at the node in any of the designated 

 ways, but remained entirely separate. Barton did not interpret this 

 pattern as representing a separate category of nodal filament structure, 

 however, because she felt she had plants with "all gradations of the 

 character from filaments with well-developed pits to those which were 

 entirely free and shewed even no trace of thin places on their unusually 

 thick walls". Consequently those that she did not consider to be stunted 

 or small specimens of the typical incrassata, she designated as a distinct 

 form of incrassata, f. ovata. The form epithet was chosen because these 

 plants resembled, at least externally, Agardh's incrassata v. ovata, the 

 type of which she was unable to examine microscopically. 



Although Barton was apparently satisfied with this decision, and 

 her conservatism was reasonable considering the small number of such 

 specimens available to her, the true nature of the material is more 

 interesting. I have examined all Barton's material at the British 

 Museum (Natural History) as well as the Siboga collection in the 



