<p>The mangrove ecosystem represents an extreme environment characterized by high salinity, tidal changes, strong winds, high temperatures, and muddy, anaerobic soils, where the diversity of macrofungi is often overlooked. During field surveys in the National Nature Reserve of Mangrove Swamp at the Terminal of Zhang River, Southeast China, several macrofungal specimens were sampled. Of them, two specimens collected on a mangrove species, viz. <i>Kandelia obovata</i> attracted our attention. After careful morphological examinations and multilocus-based phylogenetic analyses, a new monotypic genus <i>Allocampanella</i> and a new species <i>A. mangrovei</i> are described within <i>Campanellaceae</i>, <i>Agaricales</i>. This new species is distinguished by the presence of real lamellae, a distinct central stipe, elliptical basidiospores, and growth on the basal trunk of mangroves. The current taxonomic innovation not only improves our morphological and ecological understanding of species in <i>Campanellaceae</i>, but also enriches our knowledge of macrofungal resources in the unique mangrove ecosystem. Hopefully, future investigations in the mangrove ecosystem that is shrinking year by year could pay more attention to macrofungi.</p>