Cytogenetic Diversity and Genome Size Variation in Cuscuta L. subgenus Grammica section Subulatae (Convolvulaceae): Insights from C. argentinana Yunk. and C. parodiana Yunk

The genus Cuscuta exhibits remarkable cytogenetic diversity, strongly influenced by heterochromatin dynamics. The genus is divided into four subgenera, the subgenus Grammica is almost exclusively found in the Americas, and South America is the first major diversification center. The section Subulatae consists of species primarily found in Argentina. To cytogenetically characterize the Cuscuta species of Subulatae and investigate the chromosomal evolution of the subgenus Grammica , CMA/DAPI banding, FISH with 5S and 35S rDNA, and flow cytometry were performed on C. argentinana and C. parodiana . Both species exhibited 2 n = 30 with differences in chromosome size, heterochromatic banding patterns, and genome size. Cuscuta argentinana has smaller chromosomes and genome (1C = 1.49 Gbp) and a higher number of metacentric chromosomes and CMA⁺/DAPI⁻ bands, whereas C. parodiana (1C = 2.79 Gbp) exhibits heterochromatin accumulation and a higher number of submetacentric chromosomes and heterochromatin accumulation. While the number of 5S rDNA sites was the same (six sites), C. parodiana presented one more pair of 35S rDNA sites. The results suggest that genome variation in Cuscuta section Subulatae is associated with heterochromatin amplification. These findings contribute to understanding of Grammica diversification and the role of heterochomatin in the chromosomal evolution of the genus.