On the identity and origin of the Mediterranean invasive Caulerpa racemosa (Caulerpales, Chlorophyta)

Recent morphological and genetic studies on the Caulerpa racemosa (Forsskål) J. Agardh complex have demonstrated that three taxa occur in the Mediterranean Sea. One of them, the ‘invasive variety’, provisionally regarded as close to C. racemosa var. occidentalis J. Agardh, is currently spreading spectacularly throughout the Mediterranean. On the basis of new morphological and molecular studies (rDNA ITS1, 5.8S and ITS2 sequences), we confirm here that this invasion is the result of a recent introduction and we identify the invasive variety as Caulerpa cylindracea Sonder, endemic to south-west Australia, and currently known as C. racemosa var. laetevirens f. cylindracea (Sonder) Weber-van Bosse. C. cylindracea differs from the tropical north Australian C. laetevirens Montagne by its slender thallus, lack of large rhizoidal pillars, the slight inflation of the basal part of the upright axes immediately above the attachment to the stolon, by the range of morphological variations (branchlets clavate to cylindrical but never trumpet-like or shield-like) and by the rDNA ITS sequence data. The new combination C. racemosa var. cylindracea (Sonder) Verlaque, Huisman et Boudouresque is therefore proposed.