Colaconema zhanjiangensis sp. nov. (Colaconemataceae, Rhodophyta): a new epi-endophytic filamentous red algal species from China

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.