Caulerpa ambigua is a species of seaweed in the Caulerpaceae family found in marine waters of the Pacific Ocean near the southern end of Japan.[1] It has a limited distribution and is endemic around the Bonin Islands around south of Japan.
It has dwarf filiform (threadlike) fronds that are typically in length and only wide, tapering slightly along the length. The branches are arranged in a divaricate pattern and each branch is loosely closed with oppositely arranged scales called ramenta.[2] It is similar in appearance to Caulerpa okamurai which has a larger spread of distribution.[2]
Caulerpa ambigua was first formally described by Kintarô Okamura in 1897 as part of the work On the Algae from Ogasawara-jima (Bonin Islands) as published in Botanical Magazine, Tokyo. The specific epithet is taken from the Latin word meaning doubtful or uncertain.[1]