The taxonomy of the brown algal genus Dictyota J.V. Lamouroux has a long and troubled history. Our inability to distinguish morphological plasticity from fixed diagnostic traits that separate the various species has severely confounded species delineation. Approximately 76 species, distributed in temperate to tropical environments, are currently recognized (Solé and Foldats 2003, Tronholm et al. 2010a, Guiry and Guiry 2014). In Mexico 19 species of Dictyota have been reported, twelve of which are present in the Mexican Atlantic region (Ortega et al. 2001, Mendoza-González et al. 2007, Cetz-Navarro et al. 2008, Pedroche et al. 2008).
One of the most widely used characters to differentiate Dictyota species consist of the presence or absence of teeth or outgrowths from the thallus margin or surface, although it has been realized that at least in some species dentation shows marked intraspecific variation (De Clerck and Coppejans 1997, 1999, De Clerck 2003). Species with dentate margins are often reported as D. crenulata J. Agardh or D. ciliolata Sonder ex Kützing. Recent molecular data demonstrated considerable conflict between traditional and DNA-based species criteria for D. crenulata (Tronholm et al. 2012, 2013). The latter species, although frequently reported from Pacific Central America, the western as well as the eastern Atlantic Ocean, was shown to consist of a complex of predominantly range-restricted species. Tronholm et al. (2012) concluded that genuine D. crenulata is confined to the Central American eastern Pacific shores, while the Atlantic species segregate into the amphi-Atlanic D. jamaicensis W. R. Taylor, D. canariensis (Grunow) Tronholm and D. pleiacantha Tronholm, the latter two species apparently being confined to M...
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...2004, Tronholm et al. 2012). We therefore conclude that these samples are most likely conspecific.
Even though accumulating molecular data provide evidence for the prevalence of geographically restricted species, there is strong support that at least some seaweeds are characterized by large geographical ranges (e.g. Leliaert et al. 2009, Machín-Sánchez et al. 2012, Metti et al. 2013, Silberfeld et al. 2013, Verbruggen and De Clerck 2013). For example, in the genus Dictyota, D. jamaicensis and D. implexa (Desfontaines) J. V. Lamouroux, both of which are relatively closely related to D. canariensis, are known from the eastern as well as western Atlantic Ocean (Tronholm et al. 2010b, 2013). Increased sampling in combination with barcoding efforts will most likely reveal additional species with broad ranges and ultimately give a more balanced view of algal biogeography.