D.E. Wujek and R.H. Thompson. 2005. Endophytic unicellular chlorophytes: a review of Chlorochytrium and Scotinosphaera. Phycologia 44: 254–260.The genera Nautococcopsis and Ectogeron are reduced to synonymy with Chlorochytrium. The inclusion of Scotinosphaera and Kentrosphaera within the genus Chlorochytrium is considered now untenable. Scotinosphaera and Kentrosphaera are considered synonymous, with the name Scotinosphaera having priority. Redefinitions are given for Chlorochytrium and Scotinosphaera based on seven opposed attributes. Chlorochytrium, in germination of the zoospore, secretes an attachment disc; has fundamentally a parietal chloroplast that develops many radiate lobes, few to many pyrenoids; and the vegetative cell contains few to many minute contractile vacuoles. Its first two to four divisions are vegetative. Further division of each protoplast results in biflagellate zoospores that are walled, compressed and have a flagellar papilla. Scotinosphaera lacks an attaching disc; is strictly unicellular with no vegetative divisions; contains an axile chloroplast with many radiate arms; has characteristically one large central pyrenoid; lacks contractile vacuoles; and division results in numerous biflagellate, terete, spindle-shaped zoospores. Old cells may develop one or more localised lamellated, wart-like thickenings of the wall, externally or internally. Sexual fusion has been observed for Chlorochytrium but not for Scotinosphaera. The relationships of Chlorokoryne, Eremotyle, Nautococcus and Excentrosphaera are reviewed.