Relationship in annual species ofMedicago. I. Number and morphology of chromosomes

Ideograms are presented of the haploid chromosome set of 22 annual species and varieties of Medicago belonging to sections Spirocarpos and Orbiculares. Differences in the number, size, and morphology of the chromosomes among these species have been found. In section Spivocarpos, the 2n = 16 species belonging to subsection Pachyspirae have similar karyotypes but considerable variability occurs among species within subsection Leptospirae. Counts of 2n = 14 were recorded in 48 accessions of the three species, M. polymorpha L., M. rigidula (L.) All., and M. praecox DC. Similarity in chromosome morphology was found between the three species, but differences in the karyotypes, not correlated with the external morphology of the plants and pods, were observed between some accessions of M. polymorpha L.