Ramomarthamyces octomerus sp. nov. is described here. This apothecial fungus is described from specimens collected in Mediterranean climate regions in southern Portugal, Spain (Canary Islands), and the Dalmatian region of Croatia. Presumably saprobic, R. octomerus occurs on intact, decorticated wood of Laurus novocanariensis and Olea europaea. Ascospores are cylindric-ellipsoid and seven-septate. Surprisingly, in our four-locus phylogenetic analysis (nuSSU, ITS1-5.8S-ITS2, LSU, mtSSU), this fungus clusters among species of Cyclaneusma, Marthamyces, Naemacyclus, and Ramomarthamyces in a core Marthamycetaceae clade that circumscribes primarily leaf-inhabiting, filiform-spored species. In addition, the asci of R. octomerus possess an amyloid pore, but the reaction varies between specimens collected in the Canary Islands and those collected in Portugal and Croatia. The occurrence of an amyloid reaction in the asci of R. octomerus challenges the characterization of Marthamycetales taxa as possessing inamyloid asci. In our discussion, we provide background and analysis of these notable observations and justify our rationale for retaining R. octomerus in Ramomarthamyces rather than creating a new genus to accommodate it. We also provide notes on the laurel forest habitat of Garajonay National Park on La Gomera island, Canary Islands, Spain, which is a UNESCO World Heritage Site and where the holotype of R. octomerus was collected.

Macromorphological observations of apothecia were made using an Olympus SZX9 or a Motic SMZ-168 stereomicroscope. Photomicrographs were made using transmitted light microscopy with an Olympus BX51 compound light microscope with 40×, 100×/1.30 oil immersion plan-achromatic objectives, together with an Olympus XC50 5.0-megapixel digital camera and Olympus cellSens Standard 1.14 image processing software.

To study the structure of apothecia and tissue types following [28: pp. 32–34], longitudinal sections through the midpoint of an apothecium were made by hand-sectioning with the aid of a stereomicroscope or by using a freezing stage mounted to a sliding microtome. Hand sections were made to observe living cells and tissues. The freezing microtome apparatus facilitated making sections that were uniform and thin (~15–25 µm). To make these, pieces of substratum supporting an apothecium were hydrated, soaked in a solution of dilute gum Arabic, and oriented on an electric, water-cooled, freezing stage (Physitemp BFS-5MP) mounted to a sliding microtome. Additional dilute gum Arabic was added to completely envelop the sample in a supportive matrix so it would not be damaged during sectioning. The microtome was set to make ~ 15 µm sections for routine observation, but 20–25 µm sections or greater were routinely made for species with asci wider than 15 µm. Sections were placed in water on a microscope slide and studied with the aid of a stereomicroscope to select the widest sections, which are from the middle of the apothecium.

To study mature, living ascospores that were discharged from recently collected apothecia, we followed the procedure outlined in Karakehian et al. (2021. Asian Journal of Mycology 4(2): 1–18). Briefly, recently collected apothecia were hydrated and maintained in a moist chamber with a coverglass suspended over them to collect discharged ascospores. The cover glasses bearing living ascospores were mounted in a drop of tap water on a microscope slide and observed using transmitted light microscopy within a few hours of being discharged.

We used these same microscopy preparations to measure dead ascospores. The ascospores were killed by drawing a drop of KOH or MLZ under the cover glass. Because of this approach, we could not make measurements of individual ascospores in both living and dead states. In other words, any given measurement of a dead ascospore was likely not made from the same, single ascospore in the living state. We separated the living and dead ascospore measurements into two spreadsheets to try to avoid a user assuming that a given row represented measurements from a single, individual ascospore in both the living and dead states.