Key to 25 Mushroom-Eating Mushrooms and Fungi (Mycotrophs) 
by Michael Kuo
The mushrooms and fungi keyed out below are parasites on other mushrooms or saprobes on the remains of other mushrooms. Since so few commonly collected mushrooms play these ecological roles, their identification can be handily economized if you are sure your mushroom or fungus was growing on a mushroom. While mycotrophism is frequently obvious (as in Pseudoboletus parasiticus) it can also go unnoticed, since the "victim" mushroom can be blackened and nearly unrecognizable (as in Collybia cirrhata) or even hidden underground (as in Cordyceps ophioglossoides). For this reason most of the mushrooms below are also keyed elsewhere at the site, on the basis of their physical features.
| 1. | Mushroom growing out of another mushroom that appears to be the same species (abnormal, "freak" fruitings are not uncommon in the mushroom world, and do not actually represent mycotrophism). | Atypical mushroom |
| 1. | Mushroom growing from a different mushroom species. | 2 |
| 2. | Mycotroph not as above (though victim could still be Gymnopus dryophilus). | 3 |
| 3. | Mycotroph a crust, fuzz, or mold covering the victim. | 4 |
| 4. | Mycotroph prominently fuzzy or hairy. | 5 |
| 4. | Mycotroph not prominently fuzzy or hairy. | 6 |
| 5. | Mycotroph as scattered, spikelike hairs or dense whitish spike-fuzz on species of Mycena. | Spinellus fusiger |
| 6. | Victim a species of Helvella; mycotroph whitish to pinkish. | |
| 6. | Victim a bolete or a gilled mushroom. | 7 |
| 7. | Victim a gilled mushroom. | 9 |
| 8. | Mycotroph white throughout development; victim potentially any bolete but most commonly Suillus pictus. | |
| 8. | Mycotroph white at first, becoming yellow as it matures; victim potentially any bolete. | |
| 10. | Mycotroph greenish yellow, often confined to the stem and gills of the victim. | |
| 10. | Mycotroph bright orange, usually completely engulfing the victim by maturity. | |
| 11. | Mycotroph not a bolete; victims various. | 12 |
| 12. | Mycotroph a club-shaped fungus, with or without a clearly distinct cap; victim an underground puffball. | 13 |
| 12. | Mycotroph not a club fungus; victims various. | 17 |
| 13. | Mycotroph with a vague head area but without a clearly distinct, separate cap structure; yellow cords attaching mycotroph to victim. | |
| 13. | Mycotroph with a clearly distinct cap; yellow cords absent. | 14 |
| 14. | Mycotroph small (under 3 cm tall), with a purple-black cap and spore segments 2-5 µ long; rare. | Cordyceps fracta |
| 14. | Mycotroph larger than above (up to 11 cm tall), with variously colored caps and spore segments slightly (3-8 µ) or substantially (8-50 µ) longer than above; fairly common. | 15 |
| 15. | Mycotroph with cap and stem both dark brown throughout development; spore segments 3-8 µ long. | Cordyceps valliformis |
| 15. | Mycotroph with yellowish stem, at least when young; spore segments 8-50 µ long. | 16 |
| 16. | Mycotroph with spore segments 8-30 µ long; widely distributed in North America. | Cordyceps capitata |
| 16. | Mycotroph with spore segments 20-50 µ long; apparently limited to eastern North America. | Cordyceps canadensis |
| 17. | Mycotroph a whitish to pinkish mass of tissue near or among its victims, which are honey mushrooms--and/or among grayish gilled mushrooms with pink gills and mealy odor (which represent "normal" forms of the mycotroph). | |
| 17. | Mycotroph a gilled mushroom arising directly from its victim; victims various. | 18 |
| 18. | Mycotroph with a volva at the base of its stem; victim usually a species of Clitocybe. | Volvariella surrecta |
| 18. | Mycotroph without a volva; victims various. | 19 |
| 19. | Spore print of mycotroph white; stem of mycotroph without a ring; victims various. | 20 |
| 20. | Variously distributed; victims various gilled mushrooms (especially species of Russula). | 21 |
| 21. | Found in the Pacific Northwest and California; stem of mycotroph long and rooting, with tiny, funky side-branches. | Dendrocollybia racemosa |
| 21. | Variously distributed; stem of mycotroph not as above. | 22 |
| 22. | Mycotroph arising from a small mass of tissue (a sclerotium) or from copious white threads; stem of mycotroph about 1-2 mm wide; cap of mycotroph fairly smooth; gills of mycotroph well developed; spores of mycotroph produced only as basidiospores (on basidia located on the gills). | 23 |
| 22. | Mycotroph not arising from a sclerotium or copious threads; stem of mycotroph wider than above (usually at least 5 mm wide when mature); cap of mycotroph smooth or becoming powdery; gills of mycotroph thick and distant, or poorly formed; spores of mycotroph produced primarily as asexual chlamydospores on the cap surface or gills. | 25 |
| 23. | Mycotroph not arising from sclerotia. | |
| 23. | Mycotroph arising from sclerotia. | 24 |
| 24. | Sclerotia dark reddish brown, shaped like apple seeds. | |
| 24. | Sclerotia pale yellow to orangish, round or nearly so. | |
| 25. | Cap of mycotroph becoming powdery with maturity; gills of mycotroph poorly formed from the beginning; chlamydospores stellate-nodulose. | |
| 25. | Cap of mycotroph not becoming powdery; gills of mycotroph thick and well spaced, at least when young; chlamydospores ellipsoid to fusiform, not nodulose. | Asterophora parasitica |
Note: Jelly fungi in the genus Tremella (for example, Tremella mesenterica) are parasites on species of Stereum (like Stereum ostrea) and other wood-rotting fungi, but they parasitize the victim's mycelium and are therefore not usually recognized in the field as parasites.
This site contains no information about the edibility or toxicity of mushrooms.
Cite this page as:
Kuo, M. (2020, October). Key to 25 mushroom-eating mushrooms and fungi (mycotrophs). Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/mycotrophs.html
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