Occurrence of the endangered species N itellopsis obtusa ( C harales, C harophyceae) in western J apan and the genetic differences within and among Japanese populations

N itellopsis obtusa ( C harales, C harophyceae) are widely distributed from E urope to A sia; however, this species has been recorded in only the five lakes in central H onshu in J apan. This species was thought to be extinct in J apan, but was rediscovered in limited areas of L ake K awaguchi in central H onshu. More recently, we discovered more J apanese populations of N . obtusa in L ake B iwa in western H onshu, and it became clear that the species had a broader distribution in J apan than originally believed. In addition, although only male or female thalli have been collected at each lake, both male and female thalli were found from L ake B iwa. This is the first report of a potentially sexual population of N . obtusa in J apan. The DNA sequences of three chloroplast DNA markers, including both coding and non‐coding regions, were identical in all specimens from L ake K awaguchi and L ake N ojiri ( C entral H onshu), and differed from those of L ake B iwa and G erman specimens. Although Japanese and G erman specimens were genetically similar, J apanese specimens displayed considerable genetic diversity according to locality.