Abstract: In this paper，a species of the genus Aconitum L．from Yunnan，A．tuguancunense Q．E．Yang，was described as new．Its chromosome number and karyotype，particularly intrapopulational variation of the number of B chromosomes，were reported．The number of B chromosomes was found variable not only among individuals but also among cells within the same root tip，ranging from 0 to 12.

Key words: Aconitum tuguancunense, B chromosome