Delimitation of Sri Lankan cycad species inferred from combined morphological and molecular analyses

Delimitations of Sri Lankan Cycas species have not been fully resolved, and hence propelled a comprehensive scientific investigation. By conducting an intense island-wide survey, we examined different cycad morphospecies in Sri Lanka, studied their vegetative and female reproductive morphological features, and analyzed genetic variation using two plastid markers (trnH-psbA and trnSGUC-trnGUCC) and one nuclear marker (ITS), together with cycad DNA sequence data already available in GenBank (R), in order to delimit Sri Lankan Cycas taxa and to reveal their evolutionary relationships. Combined analysis of both morphological and DNA sequence data resolved Sri Lankan cycads into three species as C. circinalis and C. nathorstii (subsection Cycas), and C. zeylanica (subsection Rumphiae). The results revealed the presence of C. circinalis in Sri Lanka for the first time, which was previously reported as endemic to India. Differentiating C. circinalis from C. nathorstii is rather difficult if only morphological or genetic variation is considered, and this could be due to strong phylogenetic affinities that exist between these two species. Further, the combined analysis clearly identified enigmatic intermediate individuals in the population which possessed mixed morphological and genetic features of the two species of the subsection Cycas. We propose to implement combined analysis of both morphological and DNA sequence (both plastid and nuclear) data as a better approach in discriminating closely related cycad taxa, and in identifying enigmatic intermediate individuals in the population, compared to analysis of each data type separately.

Automated summary

This study delved into the delimitations and evolutionary relationships of Cycas species in Sri Lanka through an island-wide survey. The researchers analyzed morphological features, genetic markers, and DNA sequence data to identify three Cycas species in Sri Lanka. The study also revealed the presence of C. circinalis in Sri Lanka for the first time and identified intermediate individuals with mixed morphological and genetic characteristics. The authors suggest the combined analysis of morphology and DNA sequence data as a superior method for distinguishing closely related Cycas taxa.