INTRODUCTION The Cladophorophyceae, including about 30 genera, comprise a mainly marine class of siphon- ocladous (i.e., septate plants with multinucleate cells) Chlorophyta with tropical to cold-water dis- tributions. Thallus organization ranges from branched or unbranched uniseriate filaments (e.g. the genera Cladophora and Chaetomorpha) to more complex architectural types such as thalli composed of inflated cells (e.g. Valonia) to elabo- rately reticulate plants composed of anastomosing filaments (e.g. Microdictyon and Struvea). Valonia cladophora was originally described by KÜTZING (1863a: 12) based on a collection made by Eugene Vieillard in New Caledonia. The only existing authentic specimen under this name (Vieillard no. 1973, deposited in L 937,183-020) is regarded as the holotype (MILLAR & PRUD- HOMME VAN REINE 2005) and corresponds to Kützing’s original description of cushion-like plants composed of densely branched and entan- gled filaments. Later KÜTZING (1866: 1, pl. 1, figs a,b) erroneously illustrated his new species based on another specimen collected by Vieillard from New Caledonia (Vieillard no. 2087, also deposited in L 937,183-019). This specimen, annotated Valonia polyclados (nomen nudum), is characterized by a typical Valonia-type architec- ture, the branched thallus being composed of vesicular, subclavate cells, each of which pro- duces one to five branches at its distal pole. Because Valonia cladophora exhibits a typical Cladophora type of thallus architecture and branch- ing system, the taxon has been transferred to the genus Cladophora by MILLAR & PRUD’HOMME VAN REINE (2005). In doing so, the species epithet was changed in order to avoid a tautonym, the new name Short note CLADOPHORA MAMILLATA (CLADOPHOROPHYCEAE, CHLOROPHYTA): A LITTLE-KNOWN ALGAL SPECIES FROM NEW CALEDONIA Belg. Journ. Bot. 139 (1) : 120-123 (2006) © 2006 Royal Botanical Society of Belgium Frederik LELIAERT * and Eric COPPEJANS Research Group Phycology, Biology Department, Ghent University, Krijgslaan 281/S8, 9000 Ghent, Belgium ( * Author of correspondence; e-mail: frederik.leliaert@ugent.be) Received 11 August 2005; accepted 8 December 2005. ABSTRACT. — Valonia cladophora Kützing was described from New Caledonia in the 1860s, on the basis of a single specimen, but has not since been observed or studied. Prelimi- nary observations of the type specimen led to its transfer to the genus Cladophora and because of ICBN regulations the species required a new name, C. mamillata Leliaert in Millar & Prud’homme van Reine. In this paper, a detailed description of this poorly known taxon is pro- vided. Cladophora mamillata is characterized by mamillate elevations on the cross-walls, a unique feature in the genus. Morphologically, C. mamillata falls into the Cladophora section Aegagropila, where it closely resembles C. catenata (Linnaeus) Kützing, a widespread species in the Indo-Pacific and Atlantic Oceans. KEY WORDS. — Cladophora catenata, Cladophora mamillata, Valonia cladophora, New Caledonia, Pacific Ocean, Vieillard.