Macrodominikia compressa Blaszk., Niezgoda & B. T. Goto

Macrodominikia compressa (Sieverd., Oehl, Palenz., Sánchez-Castro & G. A. Silva) emend. Błaszk., Niezgoda & B. T. Goto Figs 3 A – H, 4 A, B Specimens examined. Poland. Pomeranian Province, spores from a trap pot culture inoculated with rhizosphere soil and root fragments of Ammophila arenaria from the Hel Peninsula maritime dunes (54 ° 36 ' 42 " N, 18 ° 48 ' 29 " E), 5 Aug 2021, P. Niezgoda (slides with spores nos. 3988–3990, LPPDSE). Switzerland. Two slides with holotype sporocarps and spores deposited under the accession number Z + ZT Myc 52538. Brazil. Thirty-three isotypic spores deposited under the URM 85721 accession number. Diagnosis. Differs from other genera of Dominikiaceae in (i) having subtending hyphae with a strong bend and locally very narrow lumen due to large thickening present on the inner surfaces of the subtending hyphal walls and (ii) nucleotide composition of sequences of the 45 S nuc rDNA region (see “ Discussion ” for details). Description. Forming loose to compact hypogeous clusters with 3–33 randomly distributed spores (Fig. 3 A), and spores singly in the soil. Spores glomoid, arising blastically at tips of subtending hyphae (Figs 3 B, D – H, 4 B) either branched from a parent hypha continuous with a mycorrhizal extraradical hypha (spores in clusters), or directly continuous with a mycorrhizal extraradical hypha (single spores). Spores pale yellow (4 A 3) to brownish yellow (5 C 8); globose to subglobose; (19 –) 62 (– 100) µm diam; rarely ovoid to oblong 22–81 × 66–134, to irregular; with one subtending hypha (Figs 3 A – H, 4 A, B). Spore wall composed of four layers (layers 1–4; Figs 3 B – H, 4 A, B). Layer 1, forming the spore surface, evanescent, flexible, hyaline, (0.6 –) 0.9 (– 1.4) µm thick, usually slightly swelling in PVLG and then easier to detect (Fig. 3 B – H), occasionally strongly or completely sloughed off in aged spores (Fig. 4 A, B). Layer 2 uniform (without visible sublayers), permanent, flexible to semi-flexible, smooth, hyaline, (0.8 –) 1.2 (– 1.5) µm thick, tightly adherent to layer 3 (Figs 3 B – H, 4 A, B). Layer 3 laminate, semi-rigid, smooth, pale yellow (4 A 3) to brownish yellow (5 C 8), (2.8 –) 3.8 (– 6.3) µm thick, consisting of very thin, <0.5 µm thick, sublayers tightly adherent to and not separating from each other even in vigorously crushed spores (Figs 3 B – H, 4 A, B). Layer 4 uniform, flexible to semi-flexible, smooth, concolorous with or slightly lighter than layer 3, (0.8 –) 1.0 (– 1.3) µm thick, usually only slightly separating from the lower surface of layer 3 even in vigorously crushed spores (Figs 3 B – H, 4 A, B). Layers 1–4 do not stain in Melzer’s reagent (Fig. 3 B – H). Subtending hypha concolorous with or slightly lighter than the spores; straight or recurved, usually cylindrical to funnel-shaped, rarely slightly constricted at the spore base, (9.6 –) 14.2 (– 20.4) µm wide at the spore base (Figs 3 A, B, D – H, 4 B). Walls of subtending hypha concolorous with or slightly lighter than the spores; usually with thickenings of unequal size, (5.8 –) 7.2 (– 11.0) µm vs. (4.0 –) 5.1 (– 6.0) µm thick, present on the inner, opposite surfaces of the walls, making the subtending hyphal lumen more or less curved and narrow when seen in a plan view (Fig. 3 A, D, E, H); less often, both walls have the same or similar thickness, (4.0 –) 6.3 (– 8.1) µm (Fig. 3 G); subtending hyphal walls composed of four layers continuous with spore wall layers 1–4 (Fig. 3 B, D, E – H). Pore (1.0 –) 2.4 (– 7.0) µm diam, open (Fig. 3 D, E) or occluded by a curved septum continuous with spore wall layer 4; septum 0.6–1.0 µm thick, located at or up to 8.2 µm below the spore base (Fig. 3 G, H); subtending hyphal lumen rarely occluded by an additional septum located up to 22 µm below the spore base. Sterile hyphae hyaline, (1.8 –) 4.2 (– 5.6) µm wide. Germination unknown. Ecology and distribution. Results from our studies conclude that in the field M. compressa probably lived in arbuscular mycorrhizal symbiosis with roots of A. arenaria that colonized maritime dunes near Hel on the Hel Peninsula in northern Poland. However, no molecular analyses were performed to confirm this assumption. In a trap pot culture, M. compressa produced abundant spore communities. Oehl et al. (2014) found this species, as G. compressum, in ten locations in Switzerland, southwestern Germany, and northeastern France. It occurred in grasslands and crop rotation systems located at altitudes between 230–1505 m asl., with soils with a wide range of pH (5.7–8.0), organic carbon (9.8–45.8 g kg - 1), and different levels of plant available phosphate. There is no sequence in GenBank with> 96 % identity to the 45 S sequence M. compressa, which would suggest the presence of this species in other regions of the world.