Abstract: The present paper deals for the first time with an analysis of the karyotypes of Athrotaxis cupressoides Don and A. selaginoides Don endemic to Tasmania (Australia). Their morphology of somatic chromosomes in seed root-tip cells, chromosome measurements, and diagrams are shown in Plate 1, Table 1 and  Fig. 1  respectively,  The karyotypic formulas of the  two  species  are 2n = 22 = 22m (2SAT) and 2n = 22 = 20m(2SAT ) + 2sm according to of terminolo- gy Lexvan et al (1964). They all belong to IB type of Stebbins’(1971)karyotypic asymmetry which was reported for the first time in the higher plants by Li(1987b). Their chromosome complements are 22 = 2L + 10M₂+ 8M₁+ 2S and 22 =2L+ 10M₂+ 6M₁+ 4S respectively according to the standard defined by Kuo et al. (1972) based on relative length. The karyotype of A. selaginoides is more ad- vanced than that of A. cupressoides.   In the light of karyotypic data, the sequence of the taxo-diaceous genera (excl. Sciadopitys)  from  primitive  to  advanced  may  be  in  the  following  order: Cryptomeria,  Glyptostrobus,  Taxodium,  Metasequoia,  Sequoiadendron,  Sequoia, Athrotaxis, Cunninghamia and Taiwania. The genus Athrotaxis is closely related to Sequoia (Sequoiadendron) and Cunninghamia The peculiarity of the karyotype of Athrotaxis deserves the establishment of a new status Arthrotaxoideae (Wettste- in) L. C. Li This suggestion is also supported by the data from morphology, embryology, palynology and geography. The family Taxodiaceae is divided into six subfamilies and nine genera, as shown in the following table:
—————————————————————————————————————————————————   1. Cryptomerioideae Hida Cryptomeria D. Don 4. Arthrotaxoideae (Wettstein) L. C. Li   2. Taxodioideae Pilger Glyptostrobus Endl. Taxodim  Richard   Athrotaxis D. Don   3. Sequoideae Saxton metasequoia Miki ex Hu et 5. Cunninghamioideae Hida Cunninghamia   Cheng Sequoiadebron Buch. Sequoia Endl. R.Brown    &nb