Xylariomycetidae, Xylariales, Polystigmataceae, Polystigma
Parasitic on deciduous living leaves and shoots of Rosaceae. Stromata typically developing in late spring and summer on living leaves, producing conidia in summer and autumn, and ascospores from fallen overwintered leaves the following spring, irregular, bright red or orange, surrounded apparently by healthy leaf tissue. Sexual morph: Ascostromata usually roughly circular and covering a large area of the leaf, significantly raising the adaxial surface of the leaf, reddish-brown to black, the ostioles occasionally conspicuous. Ascomata sphaerical, immersed, distinct walls, thin-walled. Paraphyses thinly dispersed, gradually tapering towards the apex, very thin-walled, strongly inflated between the septa. Asci 8-spored, unitunicate, clavate, long-pedicellate, thin-walled in every stage, the apex obtuse, with an apical ring. Ascospores biseriate, cylindrical to ellipsoidal or obovoid, occasionally slightly curved (fabiform), hyaline, aseptate, with or without gelatinous sheath. Asexual morph: Conidial stromata irregular, yellowish-brown in very young lesions, changing to orange to reddish-brown to black on maturity, occasionally causing small creases on the leaves but without apparent significant hypertrophic lesion, composed of an upper layer of epidermal cells filled with bright orange-brown material, a middle layer of hyaline fungal cells which are angular to vertically elongated, and the lower layer resembling the upper one. Conidiomata sphaerical, epigenous or hologenous, the ostiole unnoticeable and whose quantity corresponds to the number of conidiomata, papillate or apapillate. Conidiomatal wall poorly developed and not clearly distinguishable, composed of thin layer of small hyaline thick-walled textura angularis. Conidiogenous cells nearly cylindrical, narrowing towards the upper region, which appears somewhat irregular as a result of successive conidial scars, undergoing sympodial proliferation, spreading the entire conidiomatal wall inner surface, emerging as lateral or terminal branches from short and relatively undifferentiated conidiophores. Conidia hyaline, aseptate, apparently smooth-walled, widest nearly at the base which is lanceolate to fusiform and truncate, the upper part filiform, sigmoidally curved (adapted from Cannon 1996, Dayarathne et al. 2017).
Type species: Polystigma rubrum (Pers.) DC., Fl. franç., Edn 3 (Paris) 5/6: 164 (1815)
Notes: Polystigma is the type genus of Polystigmataceae, established by Lamarck & de Candolle (1815). It is a small genus, parasitic mainly to Prunus, with almost all of the species reported with both asexual and sexual morphs (Cannon 1996). The generic name of Polystigma has been recommended for use instead of the usually associated additional names, Polystigmina and Rhodoseptoria, since it contains a greater number of species. Five taxa of Polystigmina are already synonyms of Polystigma rubrum while the type species of Rhodoseptoria is synonym of Polystigma rubrum (Réblová et al. 2016b). Suzuki et al. (2008) reported Polystigmina pallescens as the asexual state of Polystigma fulvum.
Polystigma fulvum Pers. ex DC., Fl. franç., Edn 3 (Paris) 5/6: 164 (1815)