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This study builds on recent treatments of the marine red algal family Gracilariaceae (Gracilariales) focusing in detail on Hydropuntia and Crassiphycus. Species in these two genera often present identification problems due to high levels of morphologial similarity among genetically distinct species, and high levels of phenotypic plasticity, leading to pseudocryptic speciation and homoplasies. In order to resolve long standing problems, clarify some species concepts and better understand the evolution of the group, we performed phylogenetic analyses of all plastid rbcL DNA sequences available for known Hydropuntia and Crassiphycus species, including newly sequenced specimens. Our results revealed the presence of potentially undescribed species, the existence of strong phylogeographic patterns below and above the species level and helped re-delineate morphologically similar taxa. New detailed morphological descriptions for three common yet poorly known Western Atlantic species are provided: C. secundus, C. usneoides and H. rangiferina. H. rangiferina from the Indo- Pacific is a distinct species from the true H. rangiferina and represents a putative undescribed species. We also provide a time-calibrated phylogeny for the six genera in the Gracilariales to identify past geological and climatic processes associated with their origin and diversification. 

Lobophorais a common tropical to temperate genus of brown algae found in a plethora of habitats including shallow and deep‐water coral reefs, rocky shores, mangroves, seagrass beds, and rhodoliths beds. Recent molecular studies have revealed thatLobophoraspecies diversity has been severely underestimated. Current estimates of the species numbers range from 100 to 140 species with a suggested center of diversity in the Central Indo‐Pacific. This study used three molecular markers (cox3,rbcL,psbA), different single‐marker species delimitation methods (GMYC,ABGD,PTP), and morphological evidence to evaluateLobophoraspecies diversity in the Western Atlantic and the Eastern Pacific oceans.Cox3 provided the greatest number of primary species hypotheses(PSH), followed byrbcL and thenpsbA.GMYCspecies delimitation analysis was the most conservative across all three markers, followed byPTP, and then ABGD. The most informative diagnostic morphological characters were thallus thickness and number of cell layers in both the medulla and the dorsal/ventral cortices. Following a consensus approach, 14 distinctLobophoraspecies were identified in the Western Atlantic and five in the Eastern Pacific. Eight new species from these two oceans were herein described:L. adpressasp. nov.,L. cocoensissp. nov.,L. colombianasp. nov.,L. crispatasp. nov.,L. delicatasp. nov.,L. dispersasp. nov.,L. panamensissp. nov., andL. tortugensissp. nov. This study showed that the best approach to confidently identifyLobophoraspecies is to analyzeDNAsequences (preferablycox3 andrbcL) followed by comparative morphological and geographical assessment.