Erysiphe alphitoides  

Mycelium on both surfaces of leaves, persistent, effuse or patchy, white or pale grey, often covering the entire lamina, the leaves sometimes distorted. Appressoria lobed.
Conidiophores erect, the foot cells cylindrical, usually straight, 15-30 x 6-9 µm. Conidia formed singly, 25-40 x 13-23 µm, ellipsoidal to ovoid-ellipsoidal or doliiform, hyaline, colourless, aseptate.
Ascomata cleistothecia, 70-150 µm diam., scattered to gregarious, globose, black when mature, cracking open to reveal the asci. Peridium composed of dark brown irregularly polygonal cells 8-25 (-30) µm diam. Ascomatal appendages usually 8-18, equatorial, stiff, straight to curved, hyaline, 100-220 µm long, 5-8 µm diam., fairly thick-walled, the apex closely branched 4-6 times, the tips of the ultimate branches recurved when mature. Interascal tissue absent. Asci 5-8 per ascoma, 45-80 x 30-55 µm, sessile or shortly stalked, cracking open irregularly to release the ascospores, (4-) 6- to 8-spored. Ascospores arranged irregularly, 21-25 x 12-14 µm, ellipsoidal, aseptate, hyaline, thin-walled, without a gelatinous sheath.

Description adapted in part from Braun (1995).