An Intergeneric Hybrid in the Saxifragaceae: Evidence From Ribosomal Rna Genes

The tandemly repeated multigene families encoding the 5S and 18S‐25S ribosomal RNAs were studied at the restriction enzyme level in Tolmiea menziesii, Tellima grandiflora , and in a putative intergeneric hybrid. Using restriction endonucleases that cut once per repeat, the repeat lengths of the 5S and 18S‐25S ribosomal genes were estimated. The 5S ribosomal gene repeat length is approximately 480 and 450 base pairs, respectively, in Tolmiea and Tellima. The repeat length of the 18S‐25S ribosomal genes varied from 11–13 kb in Tolmiea , and was only about 9 kb in Tellima. The putative hybrid combined the repeat lengths of both Tolmiea and Tellima for both the 5S and the 18S‐25S ribosomal genes. These data substantiate the occurrence of natural hybridization between Tolmiea and Tellima. For both the 5S and 18S‐25S gene experiments, the hybrid appears to contain fewer repeats corresponding to Tolmiea than to Tellima.