British distribution: Widespread, locally frequent.
This is a powdery mildew, parasitic on ash (Fraxinus) species and on other generaa of the family Oleaceae, including Ligustrum and Syringa, in Britain on Common Ash (Fraxinus excelsior).
This is a powdery mildew occurring primarily on ash (Fraxinus) species. Apparently all credible British records have been on Common Ash (Fraxinus excelsior), though it can be expected on other, planted ash species. Records of "Phyllactinia guttata" on Ash belong here. This is the only powdery mildew to be expected on ash in Britain, but others might be introduced and, as always, microscopic confirmation is desirable.
The genus Phyllactinia is characterised by its radiating, spine-like cleistothecial appendages with bulbous bases, and by a dense covering of brush-like penicillate cells on the upper part of mature cleistothecia. Conidia are narrowly club-shaped, produced singly from the tips of conidiophores. Cleistothecia contain numerous asci and, in P. fraxini, individial asci contain 2–4 ascospores (generally only 2 in most other related species). Conidia are 45–100 × 12–25 µm (measurements from Braun & Cook (2012). Full descriptions are provided by Braun (1987, 1995) and by Braun & Cook (op. cit.).
For an explanatory overview of the powdery mildews and the terminology used here, go to the profile of the Erysiphales.