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/ .