Chromosome numbers and a new model for karyotype evolution in Ruppia L. (Ruppiaceae)

Abstract

Populations of three species in the genus Ruppia that inhabit the western part of the Mediterranean region were studied caryologically. All three species present bimodal karyotypes. Ruppia drepanensis Tineo ex guss. (2 n=20) has a karyotype asymmetry of the 2C type. Ruppia cirrhosa (Petagna) Grande and Ruppia maritima L. (both with 2 n=40) present a 2B asymmetry. Observations of meiosis of microspore mother cells revealed that R. drepanensis forms ten bivalents at diakinesis and Metaphase I. The other two species exhibit 20 bivalents. The long arm of subtelocentric, large chromosomes in all three species shows no sign of chiasmata at meiosis.