The evolution of genome size and r DNA in diploid species of C henopodium s.l. ( A maranthaceae)

The evolution of genome size and ribosomal DNA (r DNA ) locus organization was analysed in 23 diploid species of C henopodium s.l. , all of which share the same base chromosome number of x  = 9. Phylogenetic relationships among these species were inferred from plastid and nuclear ribosomal internal transcribed spacer (nr ITS ) DNA sequences. The molecular phylogenetic analyses assigned all analysed species of C henopodium s.l. to six evolutionary lineages, corresponding to the recent new generic taxonomic treatment of C henopodium s.l. The distribution of r DNA loci for four species is presented here for the first time using fluorescence in situ hybridization ( FISH ) with 5 S and 35 S r DNA probes. Most of the 23 analysed diploid C henopodium spp. possessed a single subterminally located 35 S r DNA locus, except for three species which possessed two 35 S r DNA loci. One or two 5 S r DNA loci were typically localized subterminally on chromosomes, rarely interstitially. Analyses of r DNA locus numbers in a phylogenetic context resulted in the reconstruction of one locus each of 35 S r DNA and 5 S r DNA , both in subterminal positions, as the ancestral state. Genome sizes determined using flow cytometry were relatively small (2 C value < 2.8 pg), ranging from 0.734 pg in C . schraderianum to 2.721 pg in C . californicum (nearly four‐fold difference), and were often conserved within major phylogenetic lineages, suggesting an adaptive value. The reconstructed ancestral genome size was small for all evolutionary lineages, and changes have probably coincided with the divergence of major lineages. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society , 2015, 179 , 218–235.