RbcL sequence analyses of Gelidium divaricatum-like specimens—mat-forming, small red algae—based on new collections from Hong Kong revealed at least three different natural lineages: two align to the current concept of the genus Gelidium (Clades I & II) and one to Gelidiophycus (Clade III). The gross morphology of the specimens in Clade I fit closely with Martens’ original illustration (1866: pl. VIII: fig. 4) and is referable to Gelidium divaricatum sensu stricto. As a type specimen of G. divaricatum has not been found, Martens’ original illustration is thus here designated as lectotype together with an epitype of a sequenced specimen from the type locality that conforms in morphology with the lectotype. Clade III clustered with Gelidiophycus divaricatus sensu Boo et al. from Hong Kong, which does not conform with Martens’ original illustration. Accordingly, we refer Gelidiophycus divaricatus sensu Boo et al. to Gelidiophycus hongkongensis S.-M. Lin & L.-C. Liu, sp. nov. Clade II aligns with material of Gelidium millarianum from Lord Howe Island, NSW, Australia and Taiwan, and is a new record for Hong Kong.