Male meiosis and chromosome numbers in seventeen species of tribe Cardueae from northwest Himalayas

The Cardueae, a tribe within the family Asteraceae, comprises approximately 1,600 species, many of which are commonly known as thistles and have significant ecological and economic importance, particularly as weeds. The chromosome number in this tribe ranges from 2n=20 to 108, based on x=12, 13, 16, or 17, although the primary base number remains unclear. This meiotic study, which includes nine genera and 17 species (34 populations) from the Northwest Himalayas, contributes new or varying cytotypes to help address the cytogenetic diversity within the tribe. The chromosome count of 2n=34 in Serratula pallida is newly reported worldwide, while Echinops echinatus (2n=30) and Centaurea calcitrapa (2n=20) are first-time reports for Indian populations. Meiotic analyses across different populations reveal a substantial occurrence of abnormalities, including chromosome stickiness, misaligned bivalents, cytomixis, and laggards, resulting in meiocytes with either fewer or additional chromosomes (aneuploidy) or entire extra sets of chromosomes (polyploidy). These abnormalities may lead to the formation of unreduced pollen grains, negatively impacting pollen viability. The high frequency of these meiotic irregularities could be a contributing factor to the variation in chromosome numbers within the tribe.