The stromata of this fungus are slender and relatively tall compared to the other species in the complex, ranging from about 0.5 cm to 3-4 cm tall by 1-3 mm wide. The fertile (peritheciate) portion ranges from about 0.3- 1.5 cm, and begins and ends abruptly. The perithecial contours are just visible beneath the surface, and there is a pale coating on the outer surface that is split into vertical striations by the perithecia developing underneath. The interior tissues are white, and softer than the black coating; the stipes are often (but not always) densely tomentose. Mature stromata are not often branched, though they may be; non-peritheciate (conidial/anamorphic) stromata may be highly branched, or not branched at all. (CAUTION: Xylaria species are nearly always impossible to identify from non-peritheciate stromata).
The perithecia are globose, 0.3-0.6 mm diam. The ostioles are very finely papillate.
The asci are monoserrate, with stipes shorter than spore-bearing parts, tipped with a I+ (reactive in Melzer’s reagent) apical apparatus 3-4.5 µm tall by 3-4 µm broad, inverted-hat shaped (flaring at the outer rim).
The ascospores are brown, unicellular, ellipsoid-inequilateral (like a flattened football) to navicular, with narrowly to broadly rounded ends. The measure 20-28 × 7-12 µm (length:width ration is usually between 2.2 and 2.8), with straight, spore-length (or nearly so) germ slit on the flattened (less curved) side of the spore.
Part of the large Xylaria arbuscula species complex, this taxon is distinguished by its larger ascospores and spore-length germslit.