British distribution: Widespread, rather common, under-recorded in some areas but also many records are suspect (see below).
This is a powdery mildew, parasitic on plantain (Plantago) species (Plantaginaceae).
This is a powdery mildew occurring on numerous plantain (Plantago) species. It is best known in Britain on Ribwort Plaintain (P. lanceolata), but is occasional on Great Plantain (P. major ssp. major) and listed also for Buck's-horn Plantain (P. coronopus) by Braun & Cook (2012). It is apparently rare on Sea Plantain (P. maritima) but there is an authentic record listed in the FRDBI. It is known on Hoary Plantain (P. media) in Europe. Another powdery mildew, Golovinomyces sordidus, is frequent to common on all of these hosts.
The genus Podosphaera is characterised in its anamorphic (asexual) state by the conidia containing fibrosin bodies (see profile of the Erysiphales). The cleistothecia each contain a single ascus. In contrast, Golovinomyces species have conidia lacking fibrosin bodies and cleistothecia with multiple asci. On plantains, P. plantaginis may coat the leaf surfaces but seems to be less conspicuous than the thick coatings developed by G. sordidus. Microscopic examination is essential for certain identification and records should not be made on field appearance alone.
Full descriptions and diagrams of the sexual and asexual stages of P. plantaginis are provided by Braun (1987, 1995) (as Sphaerotheca plantaginis) and by Braun & Cook (2012). Conidia are produced in chains, the conidia ellipsoid to barrel-shaped, 25–38 × 15–20 µm (measurements from Braun & Cook (op cit.)). Cleistothecia have short, flexuous, hyaline to brownish appendages.
It is unfortunate that the much used handbook on microfungi produced by Ellis & Ellis (1985, 1997) appears to indicate that identification may be based on host alone, they giving only P. plantaginis (as Sphaerotheca) as occuring on Plantago lanceolata, and only G. sordidus (as Erysiphe) as occurring on P. major, P. media, P. coronopus and P. maritima. While P. plantaginis is apparently the most frequent powdery mildew on Plantago lanceolata in Britain, available records suggest that it is proportionally much over-recorded on this host.
For an explanatory overview of the powdery mildews and the terminology used here, go to the profile of the Erysiphales.