Ascospore ultrastructure of Halosarpheia fibrosa (Halosphaeriales, Ascomycota)

An ultrastructural study was undertaken to characterise Halosarpheia sensu stricto by examining ascospores and appendages of the type species, H.fibrosa. At the transmission ultrastructural level, ascospores comprise a tetralaminate mesosporium with different degrees of electron density and an electron-dense episporium. In the inner three mesosporic layers, fibrils are arranged longitudinally while the outer mesosporic layer has radiating fibrils. An electron-dense delimiting membrane surrounds the whole ascospore and appendages. Appendages comprise an amorphous component of granular appearance and coiled electron-dense threads. A tiny protrusion was observed at the ascospore poles, where the appendage connects to the ascospore wall. Appendage precursor material originates from the mesosporium through discontinuities in the episporium. The ascospore wall of Halosarpheia truffifera still needs re-examination to determine the nature of the outer wall layer and to understand its taxonomic placement in Halosarpheia sensu stricto.