Ophiocordyceps sinensis
Ophiocordyceps sinensis, known colloquially as caterpillar fungus, is an entomopathogenic fungus in the family Ophiocordycipitaceae. It is mainly found in the meadows above on the Tibetan Plateau regions of Tibet, Qinghai, Sichuan, Yunnan and Himalayan regions of Bhutan and Nepal. It parasitizes larvae of ghost moths and produces a fruiting body which is valued in traditional Chinese medicine as an aphrodisiac. However, naturally harvested fruiting bodies often contain high amounts of arsenic and other heavy metals, making them potentially toxic. As a result, their sale has been strictly regulated by China's State Administration for Market Regulation since 2016.
O. sinensis parasitizes the larvae of moths within the family Hepialidae, specifically genera found on the Tibetan Plateau and in the Himalayas, between elevations of. The fungus germinates in the living larva, kills and mummifies it, and then a dark brown stalk-like fruiting body which is a few centimeters long emerges from the corpse and stands upright.
O. sinensis is classified as a medicinal mushroom, and its use has a long history in traditional Chinese medicine as well as in traditional Tibetan medicine. It is marketed for various health benefits but lacks sufficient scientific evidence for safety or effectiveness, and quality can vary due to inconsistent processing and labeling. The hand-collected, intact fungus-caterpillar body is valued by herbalists as medicine, and because of its cost, its use is also a status symbol.
The fruiting bodies of the fungus are not cultivated commercially outside of China, but the mycelium form can be cultivated in vitro. Overharvesting and overexploitation have led to the classification of O. sinensis as an endangered species in China. Additional research needs to be carried out in order to understand its morphology and growth habits for conservation and optimum utilization.
Taxonomic history and systematics
Morphological features
Ophiocordyceps sinensis consists of two parts, a fungal endosclerotium and stroma. The stroma is the upper fungal part and is dark brown or black, but can be a yellow color when fresh, and longer than the caterpillar itself, usually 4–10 cm. It grows singly from the larval head, and is clavate, sublanceolate or fusiform, and distinct from the stipe. The stipe is slender, glabrous, and longitudinally furrowed or ridged.The fertile part of the stroma is the head. The head is granular because of the ostioles of the embedded perithecia. The perithecia are ordinally arranged and ovoid. The asci are cylindrical or slightly tapering at both ends, and may be straight or curved, with a capitate and hemispheroid apex, and may be two to four spored. Similarly, ascospores are hyaline, filiform, multiseptate at a length of 5–12 μm and subattenuated on both sides. Perithecial, ascus and ascospore characters in the fruiting bodies are the key identification characteristics of O. sinensis.
Ophiocordyceps Kobayasi species produce whole ascospores and do not separate into part spores. This is different from other Cordyceps species, which produce either immersed or superficial perithecia perpendicular to stromal surface, and the ascospores at maturity are disarticulated into part spores. Generally Cordyceps species possess brightly colored and fleshy stromata, but O. sinensis has dark pigments and tough to pliant stromata, a typical characteristic feature of most of the Ophiocordyceps species.
Developments in classification
The species was first described scientifically by Miles Berkeley in 1843 as Sphaeria sinensis; Pier Andrea Saccardo transferred the species to the genus Cordyceps in 1878. The fungus was known as Cordyceps sinensis until 2007, when molecular analysis was used to amend the classification of the Cordycipitaceae and the Clavicipitaceae, resulting in the naming of a new family Ophiocordycipitaceae and the transfer of several Cordyceps species including C. sinensis to the genus Ophiocordyceps.Common names
In Tibet, it is known as yartsa gunbu, . The name was first recorded in the 15th century by the Tibetan doctor Zurkhar Namnyi Dorje. In colloquial Tibetan yartsa gunbu is often shortened to simply "bu" or "yartsa". The Tibetan name is transliterated in Nepali as यार्चागुन्बू, यार्चागुन्बा, yarshagumba, yarchagumba or yarsagumba. The transliteration in Bhutan is '.In India, it is known as keera jhar, keeda jadi, keeda ghas or ' in Nepali, Hindi and Garhwali.
It is known in Chinese as ', meaning "winter worm, summer grass", which is a literal translation of the original Tibetan name. In traditional Chinese medicine, its name is often abbreviated as chong cao, a name that also applies to other Cordyceps species, such as C. militaris. In Japanese, it is known by the Japanese reading of the characters for the Chinese name, tōchūkasō, while in Korean and Vietnamese it is known by the transliterated forms of the Chinese word, dongchunghacho and đông trùng hạ thảo respectively. Strangely, sometimes in Chinese English-language texts Cordyceps sinensis is referred to as aweto', which is the Māori name for Ophiocordyceps robertsii, a species from south-eastern Australia and New Zealand.
The English term "vegetable caterpillar" is a misnomer, as no plant is involved. "Caterpillar fungus" is a preferred term.
Synonyms
Since the 1980s, 22 species in 13 genera have been attributed to the anamorph of O. sinensis.| Anamorph | Correct Teleomorph | Method for identification/Reference |
| Cephalosporium acreomonium | Umbelopsis | |
| Chrysosporium sinense | ? | RAPD polymorphism similarity |
| Cephalosporium dongchongxiacae | O. sinensis | |
| Cephalosporium sp. sensu | O. sinensis | |
| Hirsutella sinensis | O. sinensis | ; ITS sequence; microcyclic conidiation from ascospores and molecular studies |
| Hirsutella hepiali | O. sinensis | |
| Cephalosporium sinensis | Possibly O. sinensis | there is lack of valid information |
| Isaria farinosa | Paecilomyces farinosus | |
| Isolates reported as Isaria sp., Verticella sp., Scydalium sp. | Unknown, identification is dubious | |
| Mortierella hepiali | Unknown Zygomycota | |
| Paecilomyces sinensis | ? | molecular evidence |
| Sporothrix insectorum | ? | molecular evidence |
| Paecilomyces lingi | ? | incomplete information, only appeared in one article |
| Tolypocladium sinense | ? | no valid information as of 2002 |
| Paecilomyces hepiali | ? | Confirmed to be its own species, now Samsoniella hepiali |
| Tolypocladium sinense | ? | no valid information as of 2002 |
Additional synonyms for the teleomorph are Cordyceps nepalensis and C. multiaxialis. They have similar morphological characteristics to O. sinensis, also had almost identical or identical ITS sequences and its presumed anamorph, H. sinensis.
Ecology and life cycle
The caterpillars prone to infection by O. sinensis generally live underground in alpine grass and shrub-lands on the Tibetan Plateau and the Himalayas at an altitude between. The fungus is reported from the northern range of Nepal, Bhutan, and also from the northern states of India, apart from northern Yunnan, eastern Qinghai, eastern Tibet, western Sichuan, southwestern Gansu provinces. Fifty-seven taxa from several genera are recognized as potential hosts of O. sinensis.The stalk-like dark brown to black fruiting body grows out of the head of the dead caterpillar and emerges from the soil in alpine meadows by early spring. During late summer, the fruiting body disperses spores. The caterpillars, which live underground feeding on roots, are most vulnerable to the fungus after shedding their skin, during late summer. In late autumn, chemicals on the skin of the caterpillar interact with the fungal spores and release the fungal mycelia, which then infects the caterpillar.
The infected larvae tend to remain underground vertical to the soil surface with their heads up. After invading a host larva, the fungus ramifies throughout the host and eventually kills it. Gradually the host larvae become rigid because of the production of fungal sclerotia. Fungal sclerotia are multihyphal structures that can remain dormant and then germinate to produce spores. After overwintering, the fungus ruptures the host body, forming the fruiting body, a sexual sporulating structure from the larval head that is connected to the sclerotia in the dead larva below ground and grows upward to emerge from the soil to complete the cycle.
The slow growing O. sinensis grows at a comparatively low temperature, i.e., below 21 °C. Temperature requirements and growth rates are crucial factors that distinguish O. sinensis from other similar fungi. Climate change is suspected to be negatively affecting the mountain organism.
Use in traditional Asian medicines
The use of caterpillar fungus as folk medicine apparently originated in Tibet and Nepal. So far the oldest known text documenting its use was written in the late 15th century by the Tibetan doctor Zurkhar Nyamnyi Dorje in his text: , where he describes its use as an aphrodisiac.The first mention of Ophiocordyceps sinensis in traditional Chinese medicine was in Wang Ang's 1694 compendium of materia medica, Ben Cao Bei Yao. In the 18th century it was listed in Wu Yiluo's Ben cao cong xin. The ethno-mycological knowledge on caterpillar fungus among the Nepalese people is documented. The entire fungus-caterpillar combination is hand-collected for medicinal use.
In traditional Chinese medicine, it is regarded as having an excellent balance of yin and yang as it is considered to be composed of both an animal and a vegetable.
Wild-collected "cordyceps" is not always true O. sinensis, even when the location and the host insect matches. This has resulted in the description of new species such as Cordyceps liangshanensis and Samsoniella hepiali. Despite not being the same species when examined using a modern method, these species are used in broadly the same way in traditional medicine. There are also "cordyceps" species that are traditionally known to be different from O. sinensis but nevertheless thought to be have a similar tonifying action. China is home to at least 299 species of "cordyceps" in this broadest sense.
It is marketed for various health benefits but lacks sufficient scientific evidence for safety or effectiveness, and quality can vary due to inconsistent processing and labeling.