Xylaria hypoxylon

The fruiting bodies (ascocarps) are the most reliable way to recognize Xylaria hypoxylon: erect, cylindrical to flattened structures 3–8 centimeters tall and only 2–8 millimeters thick, often twisted or bent and sparsely branched into a shape resembling a stag's antlers.

Appearance changes markedly with the season. Specimens collected in spring may be covered entirely in a white to grayish powdery coating, made up of asexual spores called conidia. Later in the year the mature ascocarp turns charcoal-black and develops minute pimple-like bumps called perithecia across its surface. These are tiny spore-producing chambers, each with a small pore, or ostiole, through which sexual spores (ascospores) are released. The perithecia sit embedded in the stroma, the tough, elastic, white internal flesh of the fruiting body.

Microscopically, the asci measure about 100 by 8 micrometers. The ascospores themselves are kidney-shaped, black, and smooth, measuring 10–14 by 4–6 micrometers, while the asexual mitospores are smooth, ellipsoid, and colorless (hyaline).

Several related Xylaria species can be mistaken for this one, most notably Xylaria polymorpha, which is thicker-bodied and branches far less than X. hypoxylon.

Xylaria hypoxylon grows in clusters on decaying hardwood, appearing directly on rotting logs, stumps, and buried wood debris. It is also known to cause root rot in living hawthorn and gooseberry plants, showing that it can act beyond simple deadwood decay in some hosts.

Observation records show a strong seasonal pattern, with reported sightings rising sharply from a late-summer low in July and August to a pronounced peak in September through November, before tapering off again in winter. This pattern likely reflects when the fruiting bodies are most visible and actively producing spores, rather than year-round abundance. As the accompanying data are presence records rather than population counts, they indicate where and when the fungus has been noticed, not how common it is or the full extent of its range.

1. Xylaria hypoxylon is bioluminescent, one of a limited number of fungi known to glow.
2. Its many common names — candlestick fungus, candlesnuff fungus, carbon antlers, and stag's horn fungus — all describe the same antler-like, blackened fruiting body.
3. Chemical studies of cultures of Xylaria hypoxylon (strain AT-028) have identified new tetralone-derivative compounds produced by the fungus.
4. Researchers have compared the cultural characteristics of X. hypoxylon with related species such as X. persicaria, X. magnoliae, and X. carpophila, including collections of X. hypoxylon with unusually small ascospores.