RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISMS DISTINGUISH AMONG ACCESSIONS OF CERATOPTERIS-THALICTROIDES AND C-RICHARDII (PARKERIACEAE)

We have used cDNA clones as probes on Southern blots to detect restric tion fragment length polymorphisms among seven Ceratopteris thalictroi des accessions, three C. richardii accessions, and one putative inters pecific hybrid. We found that the stringency of post-hybridization was hes was a critical parameter affecting the quality of our blots; even with homologous cDNA sequences low stringency conditions resulted in a smear of signal, but high stringency washes gave blots with distinct bands. Most probes showed hybridization with four or more genomic frag ments. Similarities in the number and size of fragments between and wi thin species indicated that (i) C. richardii shows limited polymorphis m among accessions tested, (ii) C. thalictroides is highly polymorphic , and (iii) Hawaiian accessions of C. thalictroides are divergent rela tive to their continental cohorts and among themselves. The putative i nterspecific hybrid did not group closely with either of these species .