| 1. | Stromata on wood, fruits or leaves, sometimes buried in soil | 2. |
| Stromata emerging from soil, not associated with recognizable plant parts | 11. | |
| 2. | Stromata growing from degraded fruits or leaves | 3. |
| Stromata on rotten wood | 5. | |
| 3. | Stromata narrow and wiry in consistency, the ascomata arranged irregularly and most of their fruit-bodies exposed; on rotten leaves of deciduous trees | Xylaria filiformis |
| Stromata cylindrical, irregular, the ascomata ± immersed with only the ostiolar regions exposed; on buried fruits of deciduous trees | 4. | |
| 4. | Stromata emerging from rotten Fagus cupules; ascospores 10-16 x 4-5 µm | Xylaria carpophila |
| Stromata on buried fruits of Crataegus; ascospores 10-14 x 4.5-6 µm | Xylaria oxyacanthae | |
| 5. | Stromata frequently branched | 6. |
| Stromata not or rarely branched | 8. | |
| 6. | Stromata initially white at the apex due to conidial production, slender, terete and often tomentose below and usually laterally flattened towards the apices; on rotten wood, branches and stumps of many deciduous trees | 7. |
| Stromata initially orange-brown at the apex, very elongate (total length up to 47.5 cm); ascospores 8.5-11.5 x 3.4-4.5 µm with a short variously oriented germ slit; developing from wood deeply buried in soil | Xylaria friesii | |
| 7. | Ascospores 13-15 x 4.5-6 µm with a straight germ slit extending the length of the spore | Xylaria hypoxylon |
| Ascospores 16-20 (-22) x 4.5-7 µm, with a short inconspicuous germ slit | Xylaria digitata | |
| 8. | Stromata small, usually sessile and acute-tipped, when young with a grey coat that splits longitudinally to reveal the stroma surface | Xylaria cinerea |
| Stromata medium-sized to large, not acute-tipped | 9. | |
| 9. | Stromata short and capitate, with a broad shallowly domed upper surface | Xylaria crozonensis |
| Stromata large, clavate to cylindrical, with a rounded apex | 10. | |
| 10. | Stromata 1-5 cm diam., irregular in shape but usually ± clavate, sometimes branched at the base; ascospores 20-32 x 5-12 µm with a straight germ slit; on dead stumps and logs, especially of Fagus | Xylaria polymorpha |
| Stromata rarely more than 1 cm diam., usually unbranched and sometimes with a long stipe; ascospores 11-17 x 5-7 µm with a long slightly helical germ slit; usually on Acer pseudoplatanus | Xylaria longipes | |
| 11. | Stromata emerging from a prominent basal bulbous structure; ascospores 9-12 (-14) x 3.5-5.5 µm | Xylaria bulbosa |
| Stromata not formed from a bulb-like structure, slender and frequently branched with acute apices; ascospores (5.5-) 6.5-9 x 3-5 µm; in manured soil | Xylaria guepinii |