Note: The morphological plasticity of Caulerpa is well known to anyone who has attempted to put names on individual specimens. Attempts to give taxonomic recognition to every variant have led to a cumbersome classification involving species, varieties, and forms expressed in an equally cumbersome nomenclature. Single plants that exhibit two or more taxonomically recognized forms have often confounded those who work with this genus. While it has long been assumed that much of this diversity is not genetically fixed, experimental evidence for this assumption has only recently been provided (e.g., Ohba & Enomoto, 1987 and Ohba, Nashima, & Enomoto, 1992). Even after forms assigned to one taxon are shown to be alternative environmentally induced expressions of forms assigned to a different taxon, taxonomists have reason to hesitate before making appropriate changes in the dauntingly complex classification and nomenclature of the genus. All such changes would have to be considered especially tentative in view of further changes that very likely will be suggested by future analyses of morphological variation.Coppejans (1992) treated the most variable species of the genus, namely, C. cupressoides, C. racemosa, and C. serrulata, as comprising morphological facies which he designated ecads. An ecad may be defined as a form that is adapted to a particular habitat but whose characters resulting from this adaptation are not genetically fixed. Because "ecad'' is a category not recognized by the ICBN, this treatment could be seen as a means of obviating nomenclatural problems. However, while this treatment has the advantage of admitting that these variants are not genetically fixed, there seems to be little or nothing to be gained by writing, with reference to C. cupressoides, "intermediate between ecad lycopodium-disticha and ecad lycopodium-elegans'' rather than "intermediate between forma disticha and forma elegans''. In the present treatment, we have integrated proposed synonymies but have refrained from making new nomenclatural combinations except in one instance.
Art. 24.1 states that "The name of an infraspecific taxon is a combination of the name of a species and an infraspecific epithet connected by a term denoting its rank.'' In other words, the name of an infraspecific taxon is a trinomial. For purposes of nomenclature, there are no quadrinomials or quinquenomials. The example given under Art. 24.1 makes it clear that in writing C. racemosa var. clavifera forma reducta, Børgesen (1907: 378) was giving the taxonomic opinion that his new form of C. racemosa should be placed under the variety clavifera. For purposes of nomenclature (as distinguished from taxonomic opinion) this name should be expressed simply as C. racemosa forma reducta. Moving this form to any other variety of C. racemosa does not require a new combination, contrary to current practice. Thus, we can write C. racemosa var. racemosa forma reducta Børgesen or C. racemosa var. peltata forma reducta Børgesen. In this catalogue, the varietal placement of a form is enclosed in brackets to emphasize that it is a taxonomic statement rather than a nomenclatural act.
Caulerpa agardhii Weber-van Bosse, 1898: 382–383, pl. XXXIV: fig. 7 (type locality: "les côtes Nord-Ouest de la Nouv.-Holland'').
INDIAN OCEAN DISTRIBUTION: Australia.