Aneuploidy and chromosome number variation in the genus <i>Impatiens</i> from the riparian habitats of the Beas River, Himachal Pradesh, India

Aneuploidy, characterized by an alteration in the normal chromosomal number, disrupts genomic stability and can negatively affect organismal fitness by reducing fertility and causing developmental abnormalities. In the genus Impatiens L. (Balsaminaceae), aneuploidy is relatively common and may contribute to genetic diversity and reproductive variation. Somatic chromosome counts ranged from 2n=12 to 2n=20, indicating the occurrence of both aneuploid and diploid cytotypes. In this study, cytomorphological observations were conducted on 18 accessions representing seven species of Impatiens L., collected from riparian habitats along the Beas River, Himachal Pradesh, India, at altitudes ranging from 1,000 to 3,000 m. Among these, seven new aneuploid cytotypes were documented for the first time worldwide in the following species: I. amphorata (2n=12, 16), I. balsamina (2n=16), I. brachycentra (2n=18, 20), I. glandulifera (2n=14), and I. laxiflora (2n=12). Intraspecific cytotypic variation was evident, suggesting chromosomal instability and potential hybridization. Meiotic irregularities—such as laggards, chromosomal stickiness, bridges, and abnormal microsporogenesis—were frequently observed, contributing to reduced pollen viability, which ranged from 65.47 to 97.84%. These findings underscore the importance of aneuploidy and meiotic irregularities in shaping genetic diversity, adaptation, and speciation in Impatiens L., and provide valuable cytogenetic data to support taxonomic classification and conservation strategies in the Himalayan biodiversity hotspot.