Inocybe chondroderma — Cartilage-top fibrecap, cartilage-top fibrehead

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Cartilage-top fibrecap2, photograph by Adolf Ceska.

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Cartilage-top fibrecap2, A. Habit; B. Cystidia, microscopic, thick-walled cells located on gills; C. Microscopic basidiospores, sketches by Oluna Ceska.

Poisonous

Gills: Adnate, pale grey-brown then brown
Spore Print: Yellowish-brown


Odour: Like sperm, not strong.
Cap: 1–5 cm in diameter, conical when young, expanding to become convex or flattened. Often with an umbo. Yellowish or orangish brown and smooth in the centre, paler and fibrous near the margin.
Gills: Close together, narrow, adnate, may pull away from the stem when drying, initially pale grey-brown or yellowish brown, darkening to brown as spores mature. With a hand lens, gill edges are paler than the sporulating gill surfaces.
Stems: 2.5–8 cm long x 0.4–0.8 cm wide, cylindrical, enlarging sometimes at the base, white to pale tan or yellowish, fibrous, top is pruinose, covered by fine fuzz visible with a hand lens.
Ring or veil: Inconspicuous, or may have wisps of veil tissue at cap margin.
Cup: None.
Spores: 7–10 (11.5) x (4.0) 4.5–5.5 (6.0) µm, almond- or bean-shaped, brown and smooth.
Cystidia: These elongate, thin- or thick-walled cells on the edge and faces of the gills are shaped variously like clubs or bottles, with a cap of minute crystals. See the sketch above.
Habitat: On soil or in duff, leaf litter, under Garry oak (Quercus garryana), or conifers including Douglas fir (Pseudotsuga menziesii) and grand fir (Abies grandis)4, ectomycorrhizal.
Geographical distribution: Pacific northwest and BC.

This typical fibrecap grows from soil, is relatively small, and its caps are fibrous and conical or bell-shaped. Distinguishing the cartilage fibrecap from the several other fibrecap species with similar colour and size can be challenging. In its original description, the species was distinguished from other similar species using a chemical test; a blue colour resulted when flesh of the cap or stem was placed in PDAB (4-(dimethylamino)benzaldehyde)3. Microscopic characters are helpful, and the basidiospores' shapes and sizes rule out many other possible species. Even though this species is common, it was not formally described until 2013 and several similar species have yet to be described and named3.

Due to fibrecaps' small size and unpleasant odour, dogs have been more likely than humans to eat them and to be poisoned5. Fibrecaps have usually been identified to genus and not to species in the poisoning cases, and so it is difficult to be sure which species are most frequently responsible for illness.

Toxins6: Cartilage-top fibrecaps contain muscarine7. Muscarine acts by mimicking the neurotransmitter acetylcholine and incorrectly transmitting nerve impulses to smooth muscles.

Symptoms7: Time of onset usually between 15 min and 2 hours, occasionally 5 hours or longer, usually ending in 24 hours. 'SLUDGE' symptoms result, Salivation, Lacrimation (excess tear formation); Urination; Diarrhoea; Gastrointestinal upset; Emesis (vomiting)8.

Treatment9: Contact your regional Poison Control Centre if you or someone you know is ill after eating fibrecaps. Poison centres provide free, expert medical advice 24 hours a day, seven days a week. If possible, save the mushrooms or some of the leftover food containing the mushrooms to help confirm identification.

Poison Control:
British Columbia: 604-682-5050 or 1-800-567-8911.
United States (WA, OR, ID): 1-800-222-1222.

1
MyCoPortal. Mycology Collections Portal, <http://mycoportal.org/portal/collections/harvestparams.php> accessed March 2018.
2
Specimen Inocybe chondroderma UBC F19355 MO64022, GenBank #HQ604092.
3
Matheny, P. B., Norvell, L. L. & Giles, E. C. A common new species of Inocybe in the Pacific Northwest with a diagnostic PDAB reaction. Mycologia 105, 436-446, doi:10.3852/12-155 (2013).
4
UBC. University of British Columbia Herbarium Database, <http://bridge.botany.ubc.ca/herbarium/database.php> accessed February 1, 2018.
5
Beug, M. W., Shaw, M. & Cochran, K. W. Thirty-plus years of mushroom poisoning: Summary of the approximately 2,000 reports in the NAMA case registry. McIlvainea 16, 47-68 (2006).
6
Berger, K. J. & Guss, D. A. Mycotoxins revisited: Part II. J. Emerg. Med. 28, 175-183, doi:10.1016/j.jemermed.2004.08.019 (2005).
7
Lurie, Y. et al. Mushroom poisoning from species of genus Inocybe (fiber head mushroom): a case series with exact species identification. Clin. Toxicol. 47, 562-565, doi:10.1080/15563650903008448 (2009).
8
USA Centers for Disease Control. Cholinesterase inhibitors: including insecticides and chemical warfare nerve agents. Part 4: The cholinergic toxidrome. Section 3: Muscarinic acetylcholine receptors. Agency for Toxic Substances and Disease Registry , Atlanta, Georgia <https://www.atsdr.cdc.gov/csem/csem.asp?csem=11&po=9> (2007) accessed June 16, 2017
9
Leikin, J. B. & Paloucek, F. P. Poisoning and Toxicology Handbook, 4th ed., CRC Press, Boca Raton, Florida (2008).