Archaeosporites rhyniensis sp. nov. C. Walker, C. J. Harper et M. Krings (Fig. 2D1)

MycoBank number: MB 556489; Index Fungorum: IF 556489; Facesoffungi number: FoF;

Holotype: A saccule with a laterally produced acaulospore present in thin section SNSB-BSPG 2016 XII 12 (Fig. 2D1) housed in the palaeobotanical collection of the SNSB- Bayerische Staatssammlung für Paläontologie und Geologie, Munich, Germany.

Diagnosis: Spores developing within neck of balloon- shaped sporiferous saccule, formed by expansion of hyphal tip that is lost as the spore becomes detached; saccule approx. 41–78 × 30–78 μm (n = 8), smooth, delicate, lacking protrusions, with a single wall approx. 1 μm thick; spores (including remains of saccule wall) 24–83 × 24–78 (mean 51 × 44; n = 248), globose to subglobose, occasionally ellipsoid, broadly ellipsoid, obovoid or ovoid, with two or three wall components, (C1–C3); C1, saccule wall, thin, flexible, up to 1 μm thick, sometimes lacking due to breakdown in substrate; main spore wall (C2) up to 3 μm thick; a very fine wall component (C3; germinal wall?), less than 1 μm thick, may be present.

Specimens examined: United Kingdom, Scotland, Aberdeenshire, Rhynie chert Lagerstätte. Besides the type specimen [mandated in Article 8.5 of the relevant International Code for Nomenclature (Turland et al., 2018) as a single specimen], more than 50 specimens are present in the type slide. Only eight of these specimens had recognizable saccules attached, although some had at least some evidence of the re- mains of the saccule surrounding the acaulospore.

Etymology: Referring to the provenance of the fossil, the Rhynie chert Lagerstätte.

Type locality: Rhynie, Aberdeenshire, Scotland, National Grid Reference NJ 494276 (57°20′09.97″ N, 002°50′31.83″ W).

Age:    Early    Devonian;    Pragian–earliest    Emsian, 411.5 ± 1.3 Ma (Parry et al., 2011), 407.1 ± 2.2 Ma (Mark et al., 2011).

Fig. 2. Three types of acaulospore development in the neck of sporiferous saccule in extant and fossil specimens, each with corresponding graphical representation. Extant specimen, Archaeospora ecuadoriana, W5340 (modified from Fig. 2a–c in Schüßler and Walker, 2019): (A1,2) acaulosporoid; (B1,2) ambisporoid; (C1,2) entrophosporoid. Fossil specimens, Archaeosporites rhyniensis gen. et sp. nov.: (D1,2) acaulosporoid; SNSB-BSPG 2016 XII 12 (D1 is the holotype); (E1,2) ambisporoid; SNSB-BSPG 2016 XII 24; (F1,2) entrophosporoid; SNSB-BSPG 2016 XII 12.