Cordyceps

Cordyceps is a genus of ascomycete fungi (sac fungi) that includes about 600 worldwide species. Diverse variants of cordyceps have had more than 1,500 years of use in Chinese medicine. Most Cordyceps species are endoparasitoids, parasitic mainly on insects and other arthropods (they are thus entomopathogenic fungi); a few are parasitic on other fungi.

The generic name Cordyceps is derived from the ancient Greek κορδύλη kordýlē, meaning "club", and the Latin -ceps, meaning "-headed". The genus has a worldwide distribution, with most of the approximately 600 known species being from Asia (notably Nepal, China, Japan, Bhutan, Korea, Vietnam, and Thailand).

Taxonomy
There are two recognized subgenera:
 * Cordyceps subgen. Cordyceps Fr. 1818
 * Cordyceps subgen. Cordylia Tul. & C. Tul. 1865

Cordyceps sensu stricto are the teleomorphs of a number of anamorphic, entomopathogenic fungus "genera" such as Beauveria (Cordyceps bassiana), Septofusidium, and Lecanicillium.

Splits
Cordyceps subgen. Epichloe was at one time a subgenus, but is now regarded as a separate genus, Epichloë.

Cordyceps subgen. Ophiocordyceps was at one time a subgenus defined by morphology. Nuclear DNA sampling done in 2007 shows that members, including "C. sinensis" and "C. unilateralis", as well as some others not placed in the subgenus, were distantly related to most of the remainder of species then placed in Cordyceps (e.g. the type species C. militaris). As a result, it became its own genus, absorbing new members.

The 2007 study also peeled off Metacordyceps (anamorph Metarhizium, Pochonia) and Elaphocordyceps. A number of species remain unclearly assigned and provisionally retained in Cordyceps sensu lato.

Biology
When Cordyceps attacks a host, the mycelium invades and eventually replaces the host tissue, while the elongated fruit body (ascocarp) may be cylindrical, branched, or of complex shape. The ascocarp bears many small, flask-shaped perithecia containing asci. These, in turn, contain thread-like ascospores, which usually break into fragments and are presumably infective.

With the example of Ophiocordyceps unilateralis, the life cycle after the death of the host involves three stages: dead host, stroma, and perithecia. In the dead host stage, the dead insect without any structure growing on its body is observed. In the stroma stage, an elongated stalk called stroma grows from the body of the host. In the perithecia stage, fruiting bodies develop on the stroma. After the perithecia stage, spores are released to the environment to infect other hosts. O. unilateralis go through several cycles in the sequence of dead host, stroma, and perithecia phases.

Cordyceps manipulates host behavior to facilitate the transmission of spores. Examples include nest abandonment of hosts, a phenomenon known as the "death grip," in which the hosts hang under the leaves upside down and clamp themselves onto the leaves with their mandibles, and self-exposure to predators for greater transmission to other hosts.

Research


Polysaccharide components and cordycepin are under basic research and have been isolated from C. militaris. Research has found that cordycepin can ameliorate testicular damage caused by diabetes, by which it regulates the activities of antioxidant enzymes through the Sirt1/Foxo3a pathway. Cordycepin has also been evidenced to abate the pathology associated with Alzheimer’s disease with the anti-oxidative stress and autophagy activation. This implication opens up a potential treatment option for neurodegenerative diseases. From another species, Cordyceps gunnii, the extracted polysaccharides have been found to enhance the activities of natural killer cells and cytotoxic T cells in immunodeficient mice, as well as up-regulate the levels of cytokines and immunoglobulins.

In addition, Cordyceps produces mycotoxins, such as alkaloids, peptides, and polyketides, that have been found to have fatal effects on both adults and nymphs of Asian citrus psyllids. Moreover, Cordyceps-induced infection decreases activities of Asian citrus psyllids’ detoxification enzymes, such as superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST), and peroxidase (POD). As these enzymes are important in regulating immune functions, the infection in turn suppresses immune activities of Asian citrus psyllids, causing them to succumb to environmental stresses more easily. Discoveries on the effects of Cordyceps on Asian citrus psyllids provide potential solutions to citrus greening disease, or Huanglongbing.

Uses
Along with Ophiocordyceps, Cordyceps has long been used in traditional Chinese medicine in the belief it can be used to treat diseases. There is no strong scientific evidence for such uses. However, studies have found several effects of Cordyceps on health. For example, Cordyceps has been found to relieve respiratory, renal, cardiovascular, and hepatic problems, with its anti-oxidation, enhancing immunity, and anti-tumor activities. In addition, Chinese herbal formula containing Cordyceps helps with increasing mitochondrial ATP production as well as mitochondrial antioxidant capacity. Cordyceps also has nutritional value, as it contains biological components such as essential amino acids, various vitamins (B1, B2, B12, E and K), and minerals such as iron, calcium, magnesium, and zinc. Moreover, Cordyceps has been found to improve symptoms of asthma.

In popular culture
Cordyceps has appeared throughout popular culture:


 * In the video game series The Last of Us (2013present) and its television adaptation (2023present), a Cordyceps fungus infects humans, causing a zombie apocalypse and the collapse of human civilization.


 * It is the cause of the pandemic that wipes out most of humanity in Mike Carey's postapocalyptic novel The Girl with All the Gifts (2014) and its film adaptation (2016).
 * In the book The Ghost Woods by C. J. Cooke, a Cordyceps fungus gains sentience and uses human hosts to manipulate their behaviour into helping it reproduce by finding further hosts.