# Russula subnigricans (ニセクロハツ)
**Russula subnigricans** (ニセクロハツ) is a deadly poisonous basidiomycete mushroom in the family [Russulaceae](https://www.edgepedia.org/russulaceae), described by the Japanese mycologist Tsuguo Hongo in 1955, whose ingestion causes rhabdomyolysis, a breakdown of skeletal and cardiac muscle cells that can be fatal[1](https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=258989&mode=Info) • [2](https://pubmed.ncbi.nlm.nih.gov/19465932/). It is the only deadly species known in the genus *Russula*, with a reported [mortality rate](https://www.edgepedia.org/mortality-rate) of more than 50 percent[3](https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.918651/full). Its fatal toxin, identified only in 2009, is the small, highly strained carboxylic acid cycloprop-2-ene carboxylic acid[2](https://pubmed.ncbi.nlm.nih.gov/19465932/).
| Key fact | Detail |
|---|---|
| Classification | Species of *Russula* (Russulaceae, Russulales, Basidiomycota), described as *Russula subnigricans* Hongo, 1955[1](https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=258989&mode=Info) |
| Lethal toxin | Cycloprop-2-ene carboxylic acid, isolated in 2009; causes fatal rhabdomyolysis in mice, indicated by increased serum creatine phosphokinase[2](https://pubmed.ncbi.nlm.nih.gov/19465932/) |
| Mortality | More than 50 percent; the only deadly species in the genus *Russula*[3](https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.918651/full) |
| Symptoms | Vomiting and diarrhea from about 30 minutes after ingestion, then muscle pain and reddish-brown urine from myoglobin released by muscle breakdown[4](https://www.jstage.jst.go.jp/article/cpb/64/6/64_c15-01033/_html/-char/en) |
| Chemical marker | Cyclopropylacetyl-(R)-carnitine, specific to genuine *R. subnigricans* and stable under ordinary laboratory conditions[4](https://www.jstage.jst.go.jp/article/cpb/64/6/64_c15-01033/_html/-char/en) |
| Look-alikes | *R. nigricans* and *R. densifolia*, both considered edible after cooking, closely resemble it; misidentification is the primary cause of accidental poisonings[4](https://www.jstage.jst.go.jp/article/cpb/64/6/64_c15-01033/_html/-char/en) |
| Distribution | Documented in Japan, Taiwan, China, and Korea; poisoning cases also reported from the United States and Taiwan[4](https://www.jstage.jst.go.jp/article/cpb/64/6/64_c15-01033/_html/-char/en) • [5](https://wwwfs.vghks.gov.tw/001/VghksUploadFiles/341/relfile/13049/7899/04.pdf) |
## Taxonomy and identification
The species belongs to the blackening brittlegills of *Russula* subgenus Compactae (subsection Nigricantinae), a group whose members share whitish flesh that discolors on handling[1](https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=258989&mode=Info) • [6](https://pmc.ncbi.nlm.nih.gov/articles/PMC11041895/). In Japan three representative species of this group are recognized: *R. subnigricans*, *R. nigricans*, and *[R. densifolia](https://www.edgepedia.org/russula-densifolia)*; the latter two are considered edible after cooking[4](https://www.jstage.jst.go.jp/article/cpb/64/6/64_c15-01033/_html/-char/en).
The most useful field character is the color change after scratching. All three species have whitish flesh that turns reddish brown when scratched; in *R. nigricans* and *R. densifolia* the color then turns black, whereas in *R. subnigricans* the reddish-brown color is persistent[4](https://www.jstage.jst.go.jp/article/cpb/64/6/64_c15-01033/_html/-char/en). *R. densifolia* can also be told apart by its crowded gills, compared with the distant gills of *R. subnigricans*[4](https://www.jstage.jst.go.jp/article/cpb/64/6/64_c15-01033/_html/-char/en). These characters are difficult and unreliable on their own, because several similar unclassified *Russula* species share the same distant gills and color behavior[4](https://www.jstage.jst.go.jp/article/cpb/64/6/64_c15-01033/_html/-char/en).
Genuine *R. subnigricans* in Japan has been located in chinquapin forests of *Castanopsis cuspidata* in warm western areas, fruiting in summer; the similar unclassified species grow under the Japanese oak *Quercus serrata* in the rainy seasons of summer and fall[4](https://www.jstage.jst.go.jp/article/cpb/64/6/64_c15-01033/_html/-char/en). Molecular work adds a caution for other regions: a Korean study using ITS and LSU markers found that Korean material identified as *R. subnigricans* was more closely related to the North American *R. eccentrica* than to the Japanese type specimen, and should be recognized as *R. eccentrica*[7](https://pubmed.ncbi.nlm.nih.gov/24994012/).
## The toxin
Poisonings attributable to *R. subnigricans* were first documented in 1954 in Japan, but the responsible toxin remained unidentified for about 50 years[4](https://www.jstage.jst.go.jp/article/cpb/64/6/64_c15-01033/_html/-char/en). In 2009, a team at [Keio University](https://www.edgepedia.org/keio-university) led by Masanori Matsuura and colleagues isolated the toxin as cycloprop-2-ene carboxylic acid, a small, highly strained carboxylic acid, and showed that it causes fatal rhabdomyolysis in mice, indicated by an increase in serum creatine phosphokinase activity[2](https://pubmed.ncbi.nlm.nih.gov/19465932/).
Two properties explain why the toxin took so long to find. It is unstable: concentrating solutions by drying, a routine step in chemical isolation, promotes its polymerization, and polymerized cycloprop-2-ene carboxylic acid lacks toxicity[2](https://pubmed.ncbi.nlm.nih.gov/19465932/) • [4](https://www.jstage.jst.go.jp/article/cpb/64/6/64_c15-01033/_html/-char/en). In addition, misidentification of *R. subnigricans* for similar mushrooms hampered earlier chemical studies; of three candidate specimens examined in the Keio work, only the Kyoto specimen contained the toxin and proved lethal to mice[4](https://www.jstage.jst.go.jp/article/cpb/64/6/64_c15-01033/_html/-char/en).
The mechanism of muscle damage is described as depletion of ATP within myocytes, which leads to an unregulated increase in intracellular calcium and results in myocyte disintegration[8](https://journals.sagepub.com/doi/full/10.1016/j.wem.2022.03.007).
## Poisoning in humans
Typical symptoms begin approximately 30 minutes after ingestion with vomiting and diarrhea, followed by stiff shoulders, back ache, and reddish-brown urine colored by high levels of myoglobin, the oxygen-binding protein of striated muscle released when muscle cells break down, a condition termed rhabdomyolysis[4](https://www.jstage.jst.go.jp/article/cpb/64/6/64_c15-01033/_html/-char/en). When poisoning is severe, additional effects can appear, difficulty speaking, persistent convulsions, constricted pupils, unconsciousness, and cardiac decline, ultimately proving fatal.[4](https://www.jstage.jst.go.jp/article/cpb/64/6/64_c15-01033/_html/-char/en) Early recognition and intensive supportive care are described as key to survival[9](https://journals.sagepub.com/doi/10.1016/j.wem.2015.03.027).
**Documented outbreaks.** In Japan, poisonings were recorded between 1954 and 2007, including 2 deaths among 4 cases in Osaka in 1958, 2 deaths among 2 cases in Aichi in 2005, and 1 death among 3 cases in Osaka in 2007; nine individuals in Taiwan were identified with symptoms of *R. subnigricans* poisoning in 1998[4](https://www.jstage.jst.go.jp/article/cpb/64/6/64_c15-01033/_html/-char/en). In Korea, the first fatal case was reported in 2016[10](https://pmc.ncbi.nlm.nih.gov/articles/PMC13082752/). In Hunan Province, China, 20 deaths were attributed to *R. subnigricans* between 2014 and 2023, and Chinese CDC data covering 2012 to 2023 identify *R. subnigricans* and *[Amanita](https://www.edgepedia.org/amanita)* species as the leading causes of death from mushroom poisoning[10](https://pmc.ncbi.nlm.nih.gov/articles/PMC13082752/).
**Clinical series.** A retrospective study of 103 patients with confirmed or highly suspected *R. subnigricans* poisoning admitted to the Affiliated Hospital of Yunnan University between 2020 and 2024 found predominantly middle-aged patients (61.2 percent), 93.2 percent from [Yunnan Province](https://www.edgepedia.org/yunnan-province), and 93.2 percent poisoned by self-picked mushrooms[10](https://pmc.ncbi.nlm.nih.gov/articles/PMC13082752/). Symptom onset was rapid, with a median latency of 2.4 hours, and laboratory findings showed hepatotoxicity in 97.1 percent and myocardial injury in 85.4 percent of patients[10](https://pmc.ncbi.nlm.nih.gov/articles/PMC13082752/). Treatment combined conventional therapy (gastrointestinal decontamination, hepatoprotective and gastroprotective agents, and fluid resuscitation) with blood purification in 60.2 percent of cases; 91 patients (88.3 percent) recovered and were discharged[10](https://pmc.ncbi.nlm.nih.gov/articles/PMC13082752/). No specific antidote exists[10](https://pmc.ncbi.nlm.nih.gov/articles/PMC13082752/).
## Detection and identification methods
Because the toxin itself is unstable, several stable markers and DNA-based tests have been developed to identify the species.
- **Chemical marker.** Cyclopropylacetyl-(R)-carnitine, a carnitine ester specific to genuine *R. subnigricans*, is stable under ordinary experimental conditions, and its upfield cyclopropane signals in the proton NMR spectrum are easily recognizable in crude extracts[4](https://www.jstage.jst.go.jp/article/cpb/64/6/64_c15-01033/_html/-char/en). The compound itself showed no toxicity in mice by intraperitoneal administration[4](https://www.jstage.jst.go.jp/article/cpb/64/6/64_c15-01033/_html/-char/en).
- **LAMP assay.** A loop-mediated isothermal amplification assay targeting ITS regions specifically detects *R. subnigricans*, which conventional PCR could not distinguish from *R. nigricans*; the HNB-dye version reaches a sensitivity of 0.5 pg/μl, 100-fold higher than PCR, and completes in 45 minutes[3](https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.918651/full).
- **SCAR markers.** RAPD-derived SCAR primers distinguish lethal *R. subnigricans* from the edible *R. nigricans* and *R. densifolia*; the assay detects *R. subnigricans* DNA at 30 pg/μL and at 1 percent of a cooked mushroom sample[11](https://www.sciencedirect.com/science/article/pii/S0956713523006394).
- **CRISPR-based assay.** A LAMP-based CRISPR/[Cas12a assay](https://www.edgepedia.org/cas12a-assay) achieves a visual detection limit as low as 1 fg/μL of DNA and is intended for use in mushroom poisoning incidents[12](https://www.sciencedirect.com/science/article/abs/pii/S0026265X25004540).
## References
1. [NCBI Taxonomy Browser: Russula subnigricans Hongo, 1955](https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=258989&mode=Info)
2. [Matsuura M, Saikawa Y, Inui K, Nakae K, Igarashi M, Hashimoto K, Nakata M (2009). Identification of the toxic trigger in mushroom poisoning. Nature Chemical Biology 5(7):465-467.](https://pubmed.ncbi.nlm.nih.gov/19465932/)
3. [Pan L, Jiang Z, He Z, Chen Z (2022). Development of a loop-mediated isothermal amplification assay for the rapid detection of Russula subnigricans and Russula japonica. Frontiers in Microbiology 13.](https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.918651/full)
4. [Matsuura M, Kato S, Saikawa Y, Nakata M, Hashimoto K (2016). Identification of Cyclopropylacetyl-(R)-carnitine, a Unique Chemical Marker of the Fatally Toxic Mushroom Russula subnigricans. Chemical and Pharmaceutical Bulletin 64(6):602-608.](https://www.jstage.jst.go.jp/article/cpb/64/6/64_c15-01033/_html/-char/en)
5. [Mushroom poisoning case report, Kaohsiung Veterans General Hospital](https://wwwfs.vghks.gov.tw/001/VghksUploadFiles/341/relfile/13049/7899/04.pdf)
6. [Adamčík S and colleagues (2024). Stop black and white thinking: Russula subgenus Compactae (Russulaceae, Russulales) in Europe revised.](https://pmc.ncbi.nlm.nih.gov/articles/PMC11041895/)
7. [Species delimitation of three species within the Russula subgenus Compacta in Korea: R. eccentrica, R. nigricans, and R. subnigricans. Journal of Microbiology and Biotechnology (2014).](https://pubmed.ncbi.nlm.nih.gov/24994012/)
8. [Min MK and colleagues (2022). Russula subnigricans Poisoning Causes Severe Rhabdomyolysis That Could be Misdiagnosed as Non-ST Segment Elevation Myocardial Infarction. Wilderness & Environmental Medicine.](https://journals.sagepub.com/doi/full/10.1016/j.wem.2022.03.007)
9. [Lin S, Mu M, Yang F, Yang C (2015). Russula subnigricans Poisoning: From Gastrointestinal Symptoms to Rhabdomyolysis. Wilderness & Environmental Medicine.](https://journals.sagepub.com/doi/10.1016/j.wem.2015.03.027)
10. [Clinical characteristics in Russula subnigricans poisoning: a retrospective study of 103 cases (2025).](https://pmc.ncbi.nlm.nih.gov/articles/PMC13082752/)
11. [Parnmen S and colleagues (2024). Discrimination of lethal Russula subnigricans from wild edible and morphologically similar mushrooms in the genus Russula using SCAR markers. Food Control 158:110239.](https://www.sciencedirect.com/science/article/pii/S0956713523006394)
12. [Zhao Z and colleagues (2025). Ultrasensitive and visual identification of lethal mushroom Russula subnigricans by LAMP-based CRISPR/Cas12a assay. Microchemical Journal.](https://www.sciencedirect.com/science/article/abs/pii/S0026265X25004540)
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*Topic: Encyclopedia › Life and health › Microorganisms and fungi › Fungi and mycology › Basidiomycete taxa › Agaricomycetes › Russulales › Russula › Russula subg. Compactae (nigricans group)*
*Initially written Sep 17, 2026 · Reviewed: Sep 18, 2026; Oct 21, 2026 · Edited: Sep 18, 2026; Oct 11, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license