Utility of molecular-assisted alpha taxonomy of the genus Cystophora (Fucales, Phaeophyceae) from New Zealand and Australia

© 2018 International Phycological Society. Many brown macroalgal species are difficult to identify because of limited morphological differentiation and/ or high levels of plasticity. Molecular methods for distinguishing species coupled with morphological examination have been useful in clarifying species status in many groups. Cystophora is a species-rich, morphologically complex brown algal genus that has been carefully monographed, and it is ideal for testing the utility of molecular markers for genetic species delimitation. We evaluated the utility of the cytochrome oxidase subunit 1 (COI) DNA-barcode marker, alone and in combination with nuclear-encoded internal transcribed spacer (ITS) rDNA, in delimiting species. We also used several methods to delimit putative genetic species. Our results showed that for consistent species delimitation and species delimitation that approximates morphological species, both markers in combination are necessary. Most species in the genus are morphologically recognizable and genetically distinct but neither COI nor combined COI-ITS data separate Cystophora congesta from Cystophora retroflexa or Cystophora distenta from Cystophora scalaris. We showed that morphological characters used to separate these two species pairs are highly variable among samples, with many intermediates. Thus, we concluded that these are not independent species and synonymize these species. Our data showed that this genus, while widespread, mostly conforms to a morphospecies concept.