ECOLOGY AND TAXONOMY OF Halimeda 17 



nuclei equivalent to many cells but not the compartments, is a coeno- 

 cjrtic filament. 



Much of the filamentous system contains a large central vacuole 

 pushing against a thin cytoplasmic layer which is pressed to the 

 filament wall. Many of the usual microcomponents are present within 

 the filament : nuclei, plastids, smooth and rough endoplasmic reticulum, 

 free ribosomes, Golgi bodies, mitochondria, microtubules and lipid 

 globules. Some plastids, the amyloplasts, contain mostly starch. 

 Chloroplasts, with their well-developed system of photosynthetic 

 lamellae, may contain some starch as well or this may be absent. No 

 pyrenoids have been observed. The pigments present in the chloroplasts 

 are chlorophylls a and b, in a ratio usually of about 2:1, and the 

 principal carotenoids known for the other green algae. Two other 

 carotenoids, siphonoxanthin and siphonein, are also present. 



The chloroplasts, which are discoidal, are relatively small compared 

 to those of many green algae, and the nuclei are also small. Little is 

 known about the chromosomes, DNA or RNA of this alga, although 

 DNA has been reported to be present in chloroplasts and mitochondria. 



Other microcomponents of the filament include two characteristic 

 unknown bodies, one that is electron dense, the other which is spherical 

 and reticular. 



II. A Brief History of Halimeda Studies 



The first taxonomic description of a Halimeda appeared in 1599, in 

 a book of Mediterranean natural history by the naturalist Imperato 

 (Fig. 11). Using the name Sertolara he both drew and wrote about a 

 Mediterranean sea plant, which in subsequent binomial nomenclature 

 eventually was called Halimeda tuna. This Halimeda species remained 

 the only member of this taxon for more than a century, even though 

 there was considerable botanical activity at the time. Its loneness, 

 however, is not surprising, for it is the only recognized Halimeda species 

 of this essentially tropical genus that grows in the Mediterranean. 

 Authentic additions to the Halimeda species list had to await the work 

 of naturalists and collectors in areas remote from European centres 

 of learning. 



All references to Halimedae in the seventeenth century, therefore, 

 are to this one species, H. tuna, but it is heard of with many different 

 names. Clusius (1601) called it Lichen marinus. Parkinson (1640) named 

 it Opuntia marina. And in their catalogue of 1651 Bauhin and Cherler 

 listed both these names, as well as introducing two more, Fucus folio 

 rotunda and Scutellaria sive Opuntia marina. But all are the same plant. 



