A Daldinia concentrica look-alike on Alnus (alder), especially Alnus incana (grey alder), with stromata ranging from 1-6 cm in diameter, often with a nodulose (with fine bumps) surface; stromatal pigments in 10% KOH typically purple (vinaceous grey to pale violet), but sometimes olivaceous to greenish (especially in more mature or long-stored specimens), often with colour changes; with ascospores 12.5-16.5 x 6.5-7.5 µm with straight germ slits, shedding their perispores (hyaline spore coverings) in 10% KOH.
Stromata at first hemispherical to almost clavate (club-shaped), often becoming pulvinate (cushion-shaped) or placentiform (flat and rounded), sessile (unstalked) or subsessile, 1-5.8 x 1-5 x 0.9-3.4 cm; with inconspicuous to conspicuous perithecial outlines; surface dark brick to fuscous (dark purple grey) in colour, blackened and varnished in age; with dull reddish brown granules immediately beneath surface. Stromatal pigments in 10% KOH initially livid purple or dark livid purple, often changing to yellowish and occasionally olivaceous some minutes after incubation. Tissue between perithecia brown, pithy to woody; tissue below perithecial layer composed of alternating zones, darker zones dark brown, pithy to woody, 0.3-0.7 mm thick, lighter zones brown, pithy to woody, persistent, 0.5-1.5 mm thick (ratio darker/lighter zones 1:1-3). Perithecia lanceolate (lance-head-shaped in cross section) 1–1.5 x 0.3–0.4 mm. Ostioles papillate (perithecial openings with a “nipple”). Asci 200-230 x 7-11 µm, p. sp. 75-100 µm, stipes 110-140 µm, with discoid, amyloid apical apparatus, 0.75-1 x 3.5-4 µm. Ascospores brown to dark brown, ellipsoid-inequilateral, with narrowly rounded ends, 12.5-16.5 x (6-)6.5-7.5 µm, with straight germ slit spore length on convex side; perispore dehiscent in 10 % KOH, smooth by LM but showing faint transverse striations by SEM (5.000x); epispore smooth.
Description adapted from Stadler, et al. (2014). A polyphasic taxonomy of Daldinia (Xylariaceae). Studies in mycology, 77, 1-143. A more detailed description of D. petriniae and other Daldinia species, with images and keys, can be found in this open access article, available at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3953824/ .
Not formally assessed. The species was first described in 1997, and the species concept has recently been refined (see Stadler et al., 2014). In GB&I, the species has only been recorded from four sites in England, but populations may have been overlooked or misidentified as D. concentrica.
Daldinia concentrica, which primarily occurs on Fraxinus, and less frequently on members of the Betulaceae, Fagaceae and Salicaceae. In contrast, D. petriniae is only found on members of the Betulaceae, and has a strong preference for Alnus. D. concentrica stromata can be larger (2-9 cm vs. 1-6 cm diam. in D. petriniae), and have a relatively smooth or cracked stromatal surface, lacking the nodulose surface (i.e. perithecial outlines and raised ostioles) often seen in D. petriniae. Ascospores are very similar at 13-17.5 x 6-7.5 µm with a straight to slightly sigmoid (s-shaped) germ-slit, compared to 12.5-16.5 x 6.5-7.5 and a straight germ slit in D. petriniae. Stromatal pigments in 10% KOH are typically purple, sometimes weakly purple, while those of D. petriniae can be purple to greyish, changable to yellow and olivaceous tones.
Other Daldinia species may also be present but overlooked or recorded as D. concentrica in GB&I. The most current key and full descriptions of these species, can be found in Stadler et al. (2014).
Daldinia petriniae is mostly found on members of the Betulaceae, often on Alnus incana (grey alder), perhaps more frequently when the host is dead and moderately decayed. In GB, it has been recorded on Alnus sp., Alnus glutinosa (common alder), and Corylus (hazel).
In GB&I, Daldinia petriniae has been reported from single sites in North Hampshire VC12, Surrey VC17, Worcester VC37, and Warwickshire VC38.