58 L. HrLLIS-COLINVAUX 



The first two section names are taken from Agardh with spelHng 

 altered to the proper endings. The change from Tunae to Hahmeda is 

 required by the International Rules of Botanical Nomenclature, since 

 this section includes the type genus tuna. Agardh's fourth section, 

 Pseudo-Opuntiae, to which he assigned gracilis and two species of un- 

 certain identity, is redundant in this nodal filament system since 

 gracilis has been included in section Halimeda. This name, therefore, is 

 not used. Each of these three sections retains some of the species 

 originally placed in it by Agardh. 



The two new categories, Micronesicae and Crypticae, have each 

 been given the epithet (with appropriate ending) of the first species 

 described with the pattern of nodal filaments characteristic of that 

 particular section. 



Section Crypticae (at present with only one species) could, with its 

 single medullary filament, be considered an extreme form of section 

 Micronesicae. Such treatment, however, with its phylogenetic implica- 

 tions, does not seem justified by our present knowledge of the species 

 involved, which includes a distribution of Caribbean for section 

 Crypticae and Indo-Pacific for Micronesicae. I consider them two 

 separate groups. 



For all five sections the only character truly diagnostic is the pattern 

 of the filaments at the nodes. However, a few other characters, some of 

 them macroscopic, seem to be associated, fairly reliably, with the nodal 

 groups. These also are given in Table V. 



Finally, the original circumscription of the genus by Lamouroux 

 (1812) described its construction as multiaxial ("axe fibreux"). This 

 excludes the uniaxial species cryptica. Therefore, in Section IV, the 

 genus description is extended to include uniaxial as well as multiaxial 

 species. 



C. The genus Halimeda in higher taxonomy 



For the first few decades of the twentieth century Halimeda seemed 

 securely placed in the order Siphonales. But just as taxonomy within 

 the genus is changing to reflect new knowledge and concepts, so too is 

 that above the genus level. New tools such as the electron microscope 

 enable us to probe the structure of these algae more precisely, while 

 improved culture and chemical techniques provide additional data on 

 life-histories and chemical organization, and lead to new insights and 

 evaluations of the position of Halimeda and its close relatives within the 

 plant kingdom. A survey of some of the taxonomic changes is provided 



