79 records of native, adventive and cultivated taxa new to the SW Aegean island of Kithira and new localities for 51 other, little known taxa are presented. The families Isoetaceae and Ruppiaceae, and the native genera Aethionema, Arabidopsis, Crataegus, Crypsis, Echinochloa, Echinops, Isoetes, Lunaria, Moenchia and Ruppia are reported from the island for the first time. The family Amaranthaceae and the genera Aeonium, Amaranthus, Aster, Ipomoea, Mirabilis, Paspalum and Zantedeschia, which are represented by naturalized taxa, are also reported as new to the island. Morphological, chorological and other data are included for the majority of the taxa.