Unraveling the species dilemma in Capsicum frutescens and C. chinense (Solanaceae): A multiple evidence approach using morphology, molecular analysis, and sexual compatibility

The species status of two morphologically closely related species, Capsicum frutescens L. and C. chinense Jacq., was investigated using typological, phylogenetic, and biological species concepts. Diagnostic morphological differences, randomly amplified polymorphic DNA (RAPD) marker-based cluster analysis, and hybrid analyses were used to delimit C. frutescens and C. chinense. In many cases two morphological characters, calyx constriction and flower position, can separate accessions of C. frutescens from C. chinense. The RAPD-based analysis clearly separated accessions of C. frutescens and C. chinense into two distinct groups. The average genetic similarity within C. frutescens and C. chinense accessions was 0.85 and 0.8, respectively, whereas the average genetic similarity between C. frutescens and C. chinense accessions was only 0.38. The progenies obtained from C. frutescens and C. chinense hybridization had reduced fertility. Based on these evidences, C. frutescens and C. chinense represent two morphologically diagnosable, phylogenetically distinct, and reproductively isolated species.