Caulerpa taxifolia is a species of green seaweed, an alga of the genus Caulerpa, native to tropical waters of the Pacific Ocean, Indian Ocean, and Caribbean Sea. The species name taxifolia arises from the resemblance of its leaf-like fronds to those of the yew (Taxus). A strain of the species bred for use in aquariums has established non-native populations in waters of the Mediterranean Sea, the United States, and Australia. It is one of two species of algae listed in 100 of the World's Worst Invasive Alien Species compiled by the IUCN Invasive Species Specialist Group. Description C. taxifolia is light green with stolons (stems) on the sea floor, from which sparsely-branched upright fronds of approximately 20–60 cm in height arise. Algae in the genus Caulerpa synthesize a mixture of toxins termed caulerpicin, believed to impart a peppery taste to the plants. The effects of the specific toxin synthesized by C. taxifolia, caulerpenyne, have been studied, with extracts from C. taxifolia being found to negatively affect P-glycoprotein-ATPase in the sea sponge G. cydonium. Like all members of the genus Caulerpa, C. taxifolia consists of a single cell with many nuclei. The algae has been identified as the largest known single-celled organism. Wild-type C. taxifolia is monoecious. Use in aquaria Caulerpa species are commonly used in aquaria for their aesthetic qualities and ability to control the growth of undesired species. C. taxifolia has been cultivated for use in aquaria in western Europe since the early 1970s. A clone of the alga that was resistant to cold was observed in the tropical aquarium at the Wilhelma Zoo in Stuttgart and further bred by exposure to chemicals and ultraviolet light. The zoo distributed the strain to other aquaria, including the Oceanographic Museum of Monaco. The aquarium strain is morphologically identical to native populations of the species. However, a 2008 study found that a population of the aquarium strain near Caloundra, Australia exhibited markedly reduced sexual reproduction, with only male plants present during some reproductive episodes. The aquarium strain can survive out of water for up to 10 days in moist conditions, with 1 cm fragments capable of producing viable plants. Status as invasive species Outside its native range, C. taxifolia is listed as an invasive species. It is one of two algae on the list of the world's 100 worst invasive species compiled by the IUCN Invasive Species Specialist Group. The species is