Abstract
Reproductive effort in Cirsium purpuratum population growing on lapilli desert was examined. Cirsium purpuratum is the largest thistle in Japan. An experimental quadrate, 50 m × 55 m, was set on the southeast slope of Mt. Fuji at about 1700 m alt. There was a close relationship between the total leaf area in a rosette (rosette size) and the largest leaf size (length × width)in the rosette. The reproductive effort was determined by the change of each rosette size from 1997 to 1998，the numbers of produced daughter rosettes and capitula of each rosette in 1997 and 1998, and the population dynamics of seedlings from 1997 to 1999. There was a threshold for flowering in the rosette size. However the threshold for producing daughter rosettes was not determined. Our results show that this population is maintained by asexual reproduction.
