Erysiphe quercus-virginianae M. Bradshaw 2025, sp. nov.

Erysiphe quercus-virginianae M. Bradshaw sp. nov. Fig. 6 Etymology. Epithet derived from the name of the host plant, Quercus virginiana. Diagnosis. Morphologically close to Erysiphe abbreviata s. lat., but differing by forming much larger chasmothecia, 116–159 µm diam., with up to 20 appendages, and 4–8 - spored asci. Phylogenetically well-distinguished from E. abbreviata and all other North American Erysiphe spp. on oaks by forming a highly supported clade. Type. USA • North Carolina, Wake County, J. C. Raulston Arboretum, NC State University, 4415 Beryl Road, Raleigh, on Quercus virginiana planted in the arboretum, 35°47.687.10'N, 78°41.97100'W, 149 m alt., 9 November 2011, L. F. Grand s. n. (NCSLG 18481 — holotype). Ex-holotype sequence: OR 424987 (ITS + 28 S), OR 427493 (CAM), OR 427579 (GAPDH), OR 427663 (GS), OR 427727 (RPB 2), OR 427793 (TUB). Description. Mycelium and anamorph not seen. Chasmothecia scattered to gregarious among trichomes on abaxial leaf surfaces, subglobose to globose, 116–159 × 123–144 µm; peridium cells conspicuous, brown, irregularly polygonal, 12–21 × 7–14 µm; appendages 8–20, equatorial, stiff, straight to somewhat curved, aseptate, hyaline, 60–125 µm long, relative length usually about 0.5–1 times the chasmothecial diameter or somewhat shorter, 4–7 µm wide [widest at base], apices 4–5 × regularly dichotomously branched not strictly in one dimension, tips of the ultimate branchlets recurved; asci 5–8 per chasmothecium, obovoid, saccate, short-stalked, 55–75 × 40–60 µm, walls up to 3 µm thick, 4–8 - spored; ascospores ellipsoid-ovoid, hyaline, 15–25 × 8–13 µm. Additional specimen examined. USA • Florida, Broward County, Fort Lauderdale, on Quercus virginiana, 2022, M. J. Bradshaw s. n. (NCSLG 24888). Substrate / host. Quercus virginiana (Quercus subgen. Quercus sect. Virentes; Manos and Hipp 2021). Distribution. North America (USA, Florida, North Carolina). Notes. The new species, Erysiphe quercus-virginianae, is morphologically similar to the morphology-based circumscription of E. abbreviata in Braun and Cook (2012), especially with regard to the number and length of the chasmothecial appendages. However, E. abbreviata is characterized by having smaller chasmothecia, 70–110 µm diam, with fewer, 3–6 - spored, asci (3–6), and somewhat larger ascospores, 20–32 × 13–21 µm when mature. Bradshaw et al. (2025 d) published a phylogenetic-taxonomic revision of North American Erysiphe spp. on oaks, including a re-assessment of E. abbreviata. A high degree of co-evolution between Erysiphe and Quercus species was revealed in that study and led to the introduction of multiple new species as well as emended circumscriptions of several species. Based on phylogenetic examination, E. abbreviata is confined to hosts of Quercus subgen. Quercus sect. Quercus subsect. Prinoideae. Hence, it is plausible that E. quercus-virginianae, on a host of another section (Virentes) represented another, undescribed species. Quercus virginiana and all other oak species assigned to sect. Virentes are to our knowledge not hosts of E. abbreviata (not listed as hosts in Braun and Cook 2012). Amano (1986) listed Microsphaera alni and M. extensa on Q. virginiana from North America. Erysiphe extensa is a morphologically distinct species with very long chasmothecial appendages (Braun and Cook 2012; Bradshaw et al. 2025 d), whereas E. quercus-virginianae may be potentially hidden under reports of M. alni on Q. virginiana.