Abstract
The genus Ramicrusta (order Peyssonneliales) is a new record for Micronesia, with range expansions of Ramicrusta fujiiana and R. lateralis to Guam. In addition, four species (Ramicrusta adjoulanensis, R. asanitensis, R. labtasiensis, and R. taogamensis) are newly described from Guam using molecular and anatomical characters. Ramicrusta lateralis specimens from Guam share most anatomical features with the holotype description from Vanuatu, but the plants from Guam are more tightly adherent, rigid, and robust than those of Vanuatu. Ramicrusta adjoulanensis possesses a well-developed epithallus with frequent cell fusions, secondary pit connections, and lacking hair bases or trichocytes, similar to Ramicrusta bonairensis. Ramicrusta adjoulanensis differs from other Ramicrusta species in having occasionally free margins and being attached by frequently produced, relatively long rhizoids (75-100 μm long). Ramicrusta asanitensis shares features with many other species, but the thickness of the crust (upwards of 2 mm thick), heavy calcification in the epithallus, and the extent of secondary, tertiary, and quaternary growth, differentiate it from other Ramicrusta species. Ramicrusta labtasiensis shares features with its close relative Ramicrusta lateralis but possesses frequent, robust, and relatively long rhizoids (75-95 μm long) throughout its entire undersurface. Ramicrusta taogamensis resembles its close relative Ramicrusta appressa but is primarily distinguished by its generally well-developed epithallus with occasional secondary pit connections and cell fusions. The six species reported here make Guam equal to Vanuatu in currently having the highest known species richness of Ramicrusta in the world.