SummaryThe present research has been carried out on Adiantum capillus-veneris L., a well renowned medicinal fern, to study its detailed meiotic behaviour in 14 populations collected from different parts of Northwest India. All the populations uniformly revealed the presence of 30 bivalents at M-I as reported by previous workers. However, irregular meiotic behaviour characterized by the presence of stickiness, unoriented bivalents, laggards, bridges, interbivalent connections, secondary associations, cytomixis, formation of micronuclei leading to abnormal microsporogenesis, i.e., spore sterility, were investigated. The abnormal meiotic course in some studied populations has a significant effect on spore viability, i.e., reduced spore fertility. To our knowledge, this is the first ever population based report on abnormal meiotic behaviour of this species.