Abstract: Cycas panzhihuaensis L. Zhou et S. Y. Yang is a rare and endangered Cycad that grows in dry-hot valley of Jinsha River. The biological properties, trunk anatomy and growth patterns were studied by field investigation and location observation. The results showed as follows: The sex ratio of cones was strongly male based on reproductive episode. There were no significant sexual differences in leaf number, leaf size, trunk size and ramet number. More than 70% of the adult plants produce ramets, with a mean number of ramets per adult plant of about 2.8. The proportion of individuals with ramets and the number of ramets was positively correlated with trunk height. Maximum mean trunk diameter and mean number of leaves were reached when the plant reached 30--40 cm tall. Further increase of leaf width ceased when the plant reached 5 years old. Leaf reached its maximum length when the trunk was 10 cm tall. Growth units of trunk showed a linear relationship with height. The estimated age could be obtained by counting growth units of the trunk. The survival curve of leaves was well described by Deevey type Ⅰ . The survival time of many leaves was two growth units. The rate of leaf mortality abruptly increased after two growth units. Few leaves could survive five units.

Key words: Cycas panzhihuaensis, Biological properties, Trunk anatomy, Growth patterns