Chiastocaulon fimbriatum is reported new for China based on recent collections from Yunnan. It is a variable species and an updated description is provided with additional details of the newly discovered sporophytes and male plants. Chiastocaulon fimbriatum is characterized by the following features: 1) robust plant size with orbicular leaves; 2) cells in the upper part of leaf thin-walled yet with trigones; 3) leaves slightly decurrent dorsally; 4) inner bracts horizontally spreading on ventral side with multiple minute teeth on irregularly-shaped lobes; and 5) large spores. Through different stages of growth, C. fimbriatum exhibits a great variety in the shape of both leaf and perianth. The large cylindrical perianth is another important diagnostic character of this species; however, when immature, the perianths are of little taxonomic value since they can be conical or campanulate in shape at different stages of development. Based on newly obtained material, we failed to observe decurrenee of leaves on the dorsal side of the stem to be a key diagnostic feature for this species. A key for the genus in China is provided, based on specimens from Yunnan.