Abstract:The present paper breifiy reviews the history of the classification of the living cycads, and emphasizes to introduce Stevenson‘s system of cycads. In former times, all the extant genera of cycads were classified in the one family Cycadaceae (Persoon, 1807). However, in 1959, L. A. S. Johnson showed that three distinct cycad groups were better accomodated in separate families. More recently, Dennis Wm. Stevenson (1990, 1992) has carried out a series of cladistic analysis on the living cycads. He proposed a classification system of the cycads based on a cladistic analysis of fifty-two characters ranging from gross morphology to phytochemistry. Stevenson‘ system of the extant cycads is as follows：
Order Cycadales
Subord. 1. Cycadineae
Fam. 1. Cycadaceae
Only genus Cycas
Subord. 2. Zamiineae
Fam. 2. Stangeriaceae
Subfam. 1. Stangerioideae
Only genus Stangeria
Subfam. 2. Bowenioideae
Only genus Bowenia
Fam. 3. Zamiaceae
Subfam. 3. Encephalartoideae
Trib. 1. Diooneae
Only genus Dioon
Trib. 2. Encephalarteae
Subtrib. 1. Encephalartinae
Only genus Encephalartos
Subtrib. 2. Macrozamiinae
Macrozamia , Lepidozamia
Subfam. 4. Zamioideae
Trib. 3. Ceratozamieae
Only genus Ceratozamia
Trib. 4. Zamieae
Subtrib. 1. Microcycainae
Only genus Microcycas
Subtrib. 2. Zamiinae
Zamia, Chigua
The author agrees with D. Stevenson‘s classification system of the living cycads in 1992. But in practical application, infrafamilial taxa, i.g. subfamily, tribe, subtribe should be used sparingly.