Species delimitation with distinct methods based on molecular data to elucidate species boundaries in the Cycas taiwaniana complex (Cycadaceae)

Abstract Accurately delimiting species boundaries is of critical importance in many areas of biology including population genetics, conservation biology, biogeography, and evolutionary biology because inaccurate species delimitation may significantly affect downstream inferences. The Cycas taiwaniana complex consists of six morphologically similar taxa ( C. changjiangensis , C. fairylakea , C. hainanensis , C. lingshuigensis , C. szechuanensis , C. taiwaniana ) that are distributed throughout a narrow region of South China. The members of this complex and the taxonomic status of their names have long been debated. In this study, combining morphological characteristics, we employed three distinct approaches to delimit species: haplotype phylogeny delimitation, Bayesian coalescent species delimitation (BPP), and population cluster analyses. To delimitate the species boundaries within the C. taiwaniana complex, we used 4 plastid intergenic spacers (cpDNA), 4 nuclear genes (nDNA) and 10 microsatellites. All three approaches revealed the presence of two distinct species in the C. taiwaniana complex under the unified species concept, C. taiwaniana and C. szechuanensis , largely corresponding to morphological differentiation. Cycas fairylakea was a synonym for C. szechuanensis , and the other three taxa were synonyms for C. taiwaniana . Species delimitation using molecular data was consistent with our preliminary morphological inference. This study thus optimally resolved the species boundaries and taxonomic treatment of the C. taiwaniana complex from an integrated perspective using multiple sources of molecular data and distinct analytical approaches.