Polonosporaceae Błaszk., Niezgoda, B.T. Goto, Magurno, fam. nov.

MycoBank number: MB 840255; Index Fungorum number: IF 840255; Facesoffungi number: FoF;

Type: Polonospora Błaszk., Niezgoda, B.T. Goto, Magurno.

Etymology: Latin, Polonosporaceae, Polono (= from Poland) and sporaceae (= forming spores), referring to Poland, in which spores of the new family were originally found.

Diagnosis: Differs from the Archaeosporaceae and Amb- isporaceae in the number of spore walls (three-walled vs. two-walled) and the nucleotide composition of sequences of the 18S-ITS-28S nuc rDNA region and the RPB1 gene.

Description: Forming hypogeous single acaulosporoid glomerospores (= spores) directly on the neck of a sporiferous saccule (Fig. 2a, b). Spores hyaline to white (1A1), usually globose to subglobose, 80–115 μm diam, with three spore walls (spore walls 1–3; Fig. 2a–h). Spore wall 1 consisting of a short-lived, evanescent, thin layer, continuous with the wall of the sporiferous saccule, and a permanent, laminate, thicker layer (Fig. 2c–h). Spore wall 2 composed of one permanent, flexible to semi-flexible layer (Fig. 2c–h). Spore wall three permanent, coriaceous, 1.8–3.6-μm thick, composed of two tightly adherent layers (Fig. 2c–h). Only spore wall 1 layer 2 sometimes stains reddish white (7A2) in Melzer’s reagent.

Distribution and habitat: Worldwide, with records of physical specimens and environmental sequences originating from Australia, Czech Republic, China, Georgia, Japan, Norway, Poland, Portugal, and North and South Americas (Online Resource 5). Associated with roots of plants growing in dunes, forests, grasslands, hydrocarbon-polluted sites, tropical forested and cultivated soils, and wetland ecosystems

Fig. 2 Polonospora polonica. a, b. Intact spores (s) with the neck of a sporiferous saccule (nss; remnants). ch. Spore wall 1 (sw1) layers 1 and 2, spore wall 2 (sw2), and spore wall 3 (sw3) layers 1 and 2; soil debris (sd) covering the upper surface of sw1l1 and cicatrix

(c) are indicated in c. af. Spores in PVLG. g, h. Spores in PVLG + Melzer’s reagent. ah. Differential interference micros- copy. Scale bars: a, b = 20 μm, ch = 10 μm