The genera Monostroma and Gayralia belong to the order of monostromatic green algae; however, their taxonomic delimitation remains controversial at the genus level. This study attempts to address this issue through the combined analysis of the morphology and nuclear-encoded Internal Transcribed Spacer region sequences of monostromatic green algal samples collected in the South China Sea. Our phylogenetic data revealed that the monostromatic specimens were separated into the M. nitidum clade, G. brasiliensis clade, and a single Monostroma sp. clade, and that the inter-genera genetic distance between the Monostroma and Gayralia genera was lower than that observed within the Monostroma genus. All the specimens presented similar morphology in their single cell-layered thallus, with irregularly arranged cells, rounded cell corners, a parietal chloroplast, and predominantly one (>90%) pyrenoid. Their most obvious morphological difference was in thallus thickness and size. Moreover, the monostromatic specimens of the M. nitidum clade corresponded to the morphological description of the M. nitidum-type specimens. The genus Monostroma was erected earlier than the genus Gayralia. Therefore, we propose to assign the genus Gayralia to Monostroma based on the morphological and phylogenetic analysis and genetic distance data presented here.

To evaluate the nutritional value and development potential of Pterocladiella capillacea in the marine environment of Naozhou Island, Zhanjiang, this study conducted species classification and identification, followed by an analysis of key nutritional components. The combination of morphological and molecular results confirmed the identification of the collected samples as P. capillacea. Further analysis showed that P. capillacea in Zhanjiang had a moisture content of 74.9% and a protein content of 24%. In comparison, the fat (0.4%) and carbohydrate (15.4%) contents were relatively low, with moderate ash (14.3%) and crude fiber (9.1%) content. It contains a diverse range of fatty acids, with saturated fatty acids accounting for 51.82% and unsaturated fatty acids accounting for 48.18% of the total. The amino acid composition was also diverse, with essential amino acids comprising 31.58% and flavor-enhancing amino acids constituting 54.85%. The minerals contained four major elements and four trace elements, while heavy metal levels were within safety limits, ensuring their edibility. In conclusion, P. capillacea is a high-protein, low-fat economic seaweed with a favorable amino acid and fatty acid composition, rich in minerals, and with significant nutritional and developmental potential. This study provides important data to support future research and utilization of this seaweed.

The genus Colaconema represents a significant group of filamentous red algae that commonly grow as epiphytes, endophytes, or epi-endophytes on a variety of economically important macroalgae, potentially affecting host health and aquaculture productivity. Although numerous Colaconema species have been described worldwide, few have been reported from China based on integrated morphological and molecular analyses. In this study, Colaconema specimens were collected from the red macroalgae Solieria sp. in Zhanjiang City, Guangdong Province, China, and identified through detailed morphological observations combined with rbcL and 5′ region of cytochrome c oxidase subunit I (COI-5P) sequence analyses. Morphological examination revealed cylindrical cells (23–26 × 6–8 μm), irregularly branched filaments, a single plastid with a single pyrenoid, and ovoid monosporangia (11–12 × 7–9 μm) arranged in various patterns. Molecular analyses demonstrated sufficient sequence divergence from other Colaconema species (rbcL: 5.06–13.65%; COI-5P: 7.23–13.09%), supporting the recognition of these specimens as a new species. The findings expand the current understanding of species diversity within the genus.