Epiphytic non-geniculate coralline algae (ENCA) are distributed broadly, while limited research on their diversity has constrained our understanding of their ecological roles in marine environments, and impeded a comprehensive understanding of coralline algae. In this study, the diversity and ecological characteristics of ENCA epiphytic on 113 red macroalgal specimens collected from coastal China were examined. Three species delimitation algorithms revealed 24 primary species hypotheses (PSH), of which 22 were corroborated through phylogenetic analysis based on the psbA gene. Further multi-gene concatenated phylogenetic analyses and morpho-anatomical assessments revealed a new genus within Lithophylloideae, Pseudoderma gen. nov., which is closely related to the genus Titanoderma and exhibits morphological similarities. A hypothesis concerning the growth patterns was proposed to elucidate the morphological differences among Titanoderma, Lithophyllum, and Pseudoderma: the presence or absence of hypothallial palisade cells indicated distinct thallus thickening patterns, either dominated by elongation of the hypothallial cells or by division of the perithallial cells. These processes resulted in fast-growing thin-crust thalli or longer-lasting thick-crust thalli, adapted to epiphytic or epilithic lifestyles, respectively. Pseudoderma included at least six new taxa, and Pseudoderma sinicarum sp. nov., was designated as the holotype species of this genus. In conclusion, this study has underscored the unexpected biodiversity of ENCA, and the identification of the novel genus Pseudoderma from ENCA groups carried significant evolutionary implications for enhancing our understanding of coralline algae systematics.

Cryptic diversity abounds in many biological species, posing challenges to our understanding of biological diversity, conservation and management. Taking the common coralline algae, the subfamily Lithophylloideae as an illustration, this study delved into the implications of cryptic diversity through global-level phylogenetic and geographical analysis based upon Lithophylloideae molecular data worldwide, as well as a multi-locus time-calibrated phylogeny to elucidate their possible evolutionary process. The multiscale analysis revealed the polyphyly in current concept of the genus Lithophyllum. Geographic isolation resulting from the Tethys terminal event (TTE) has led to two distinct distribution regions for this so-called cosmopolitan genus: one regionally distributed along European coasts/Mediterranean that should include the taxonomical Lithophyllum; others widely distributed, particularly among pan-tropic waters, suggesting at least five groups to be rediscovered within the subfamily Lithophylloideae. Meanwhile, the cryptic genus Titanoderma, lacking morphological identification features with Lithophyllum, exhibited differences in distribution and evolutionary patterns consistent with their ecological habits, thus supporting their separation. This study provided useful hints for cryptic diversity, which advocated an integrative thinking to investigating global cryptic diversity and exploring the broad linkages between phylogenetic relationships and evolutionary origin, biogeography, morphological and ecological traits to achieve a more comprehensive understanding of biodiversity.

This chapter covers one family Porolithaceae including three subfamilies Floiophycoideae, Metagoniolithoideae, and Porolithoideae. A total of three genera three species were documented. All the species were described in detail based on Chinese specimens and accompanied line drawings clearly illustrating inner tissue and reproductive structures. Each species' habitat and distribution were also documented.

This chapter covers one family Solieriaceae belonging to order Gigartinales. Seventeen species subordinating to genera Tenaciphyllum, Eucheuma, Kappaphycus, Betaphycus, Meristotheca, Meristiella, Solieria, Sarconema, and Wurdemannia were recorded. These species were described in detail based on Chinese specimens and accompanied line drawings clearly illustrating inner tissue and reproductive structures. The species’ habitat and distribution were also documented.

This chapter covers two families, Champiaceae and Lomentariaceae belonging to order Rhodymeniales. Ten species subordinating to genera Champia, Gastroclonium, Coelothrix, Ceratodictyon, Binghamia, Fushitsunagia, and Lomentaria were recorded. These species were described in detail based on Chinese specimens and accompanied line drawings clearly illustrating inner tissue and reproductive structures. The species’ habitat and distribution were also documented.

This chapter covers three families, Ahnfeltiaceae belonging to order Ahnfeltiales, and Caulacanthaceae and Gigartinaceae of order Gigartinales. Twelve species subordinating to genera Ahnfeltia, Catenella, Caulacanthus, Chondracanthus, Chondrus, and Mazzaella were recorded. These species were described in detail based on Chinese specimens and accompanied line drawings clearly illustrating inner tissue and reproductive structures. The species’ habitat and distribution were also documented.

This chapter covers six families, two families Phyllophoraceae and Rhizophyllidaceae belonging to order Gigartinales, one family Sebdeniaceae belonging to order Sebdeniales, one family Schizymeniaceae belonging to order Nemastomatales, and two families Plocamiaceae and Sarcodiaceae belonging to order Plocamiales. Thirteen species subordinating to genera Ahnfeltiopsis, Portieria, Sebdenia, Schizymenia, Plocamium, Sarcodia and Trematocarpus were recorded. These species were described in detail based on Chinese specimens and accompanied line drawings clearly illustrating inner tissue and reproductive structures. The species’ habitat and distribution were also documented.

Gracilariaceae are economically and ecologically important red algae used to produce agar in China. Therefore, understanding the diversity of species in Chinese waters is of great academic and economic value. Although Gracilariaceae diversity in this region has been well studied in the last century, with morphological studies revealing a new genus, 16 new species, and one new variety, molecular phylogenetic studies are rare in China. The aim of this study was to construct a DNA sequence database to study the phylogeny and diversity of Gracilariaceae in this region. We generated 185 rbcL and 170 COI-5P sequences from 211 freshly collected specimens and five herbarium specimens including four types. The rbcL and COI-5P phylograms revealed 19 Gracilaria (G.) and three Gracilariopsis (Gp.) species, including one new diminutive species, Gracilaria tsengii sp. nov., which has specialized spermatangial nemathecia, and one new record for the region, G. perplexa. Based on integrated morphological and molecular analyses, G. chouae is a synonym of G. parvispora and G. firma might be a synonym of G. hainanensis, while G. articulata, G. changii, G. hainanensis, and G. yamamotoi are independent entities. This study also revealed the phylogenetic relationships between Chinese Gracilariaceae species and global taxa, which constitute a gap in several inner Gracilariales lineages compared with previous studies. Most Chinese taxa matched well with the global taxa, except for G. spinulosa, Gp. chorda, and Gp. lemaneiformis, although our collected specimens of these three species matched quite well morphologically with historical specimens. Controversial species will be better placed when molecular data from type specimens become available.

Gracilariopsis, a genus of agar-producing red seaweeds with high economic value, plays an important role in food manufacturing, pharmaceutical processing, and modern biotechnology. In this study, a wild species of red seaweed from Panama was identified as Gracilariopsis silvana by anatomy and DNA sequence data. With an aim to evaluate the response of this species to environmental conditions, changes of its PSII behaviors when exposed to gradient temperatures, salinities, and irradiances were assessed using the chlorophyll (Chl) a fluorescence transient. The PSII behaviors of this seaweed had no significant variation when the water temperature ranged from 21 to 33 °C, salinity from 12 to 40‰, and irradiance from 4 to 160 μmol photons m−2 s−1. These observations suggest that this red seaweed is able to adapt to a wide range of temperatures and salinities and has a useful characteristic of adaptation to low irradiance. Based on these results, this Gracilariopsis species is proposed as a potentially excellent red seaweed for cultivation, with great potential for benthic seaweed cultivation in low-light water layers in tropical and temperate regions.

China is rich in seaweed resources and is currently the largest seaweed producer in the world. The current study identified and investigated the geographical distribution of economically important red seaweed species around the Chinese coast, all of which are potential candidates for development in the seaweed farming industry. The study also highlighted progress made in research related to red seaweed farming in China. Farming of Pyropia and Gracilaria species continues to show steady growth, although with the occasional emergence of biological or ecological stresses. However, farming of eucheumatoid species is facing challenges because of devastating diseases and, therefore, we propose that the ‘seedling problem’ is a major obstacle in the cultivation of agarophytes and carrageenanophytes. Integrated multitrophic aquaculture systems and modern marine ranching represent the future direction of the aquaculture industry, represented by high outputs and ecologically friendly processes; seaweed farming is also likely to be able to supply feedstock for the future production of bioactive compounds and bioethanol. Overall, the utilization of red seaweeds in China is converting from traditional scattered domestic uses to modern large-scale commercial uses; thus, such high-efficiency and high-value utilization represent the future for red seaweeds in China.

We analyzed mitochondrial COI-5P and plastid rbcL sequences from specimens of Aphanta collected from China and Japan and accessed morpho-anatomical data in detail. The results revealed the presence of a novel species of this genus, Aphanta asiatica, described here. Aphanta asiatica was characterized by a turf-forming habit of thalli with anastomosing branches, and a thick, wide, and flattened axis with subpinnate to pinnate branches, and characterized by its robust and branched prostrate system bearing complex peg-like haptera which were either typical or non-typical. Rhizoidal filaments were abundant in the inner cortex and distal ends of the axis, and interspersed in the medulla. Tetrasporangial and spermatangial sori were produced on the terminal ends of the branchlets and axes. Tetrasporangia were irregularly arranged and cruciately divided, and spermatangia were cut off from the outermost cortical cells. In phylogenies of the COI-5P and rbcL sequences, A. asiatica was closely related to Aphanta pachyrrizha. In conclusion, the present study is the first to document reproductive structures in, and contribute further to our understanding of, the genus Aphanta.

In the current study, 334 specimens of Pterocladiella from China representing historical herbarium specimens and recent field collections were re-examined based upon morphological and molecular data analyses. Both datasets revealed the presence of P. beachiae, P. capillacea, P. caerulescens, and P. musciformis. Of these species, P. beachiae and P. musciformis were new records for China. Pterocladiella beachiae was characterised by a complanate thallus, with first-order short branches opposite or alternate in the upper part of the plant and marginal proliferations in the upper axis and branches; Pterocladiella musciformis had distinctive acute branch apices, cylindrical or slightly compressed lower axes, compressed upper axes, and simple irregular branches occurring either laterally or clustered. P. caerulescens had a corymbose outline and was monoecious. In the field, P. capillacea was the most common species of Pterocladiella, being widely distributed along Chinese coasts, whereas other Pterocladiella species were geographically limited in southern China. In P. capillacea, the tetrasporophyte was the dominant reproductive type while gametophytes were less common and more likely occurred in the East China Sea and South China Sea at lower latitudes.