Cyttaria darwinii (Darwin's fungus)
Darwin's fungus is a parasitic, golf ball-like fungus that was named in honour of Charles Darwin, who collected it in Tierra del Fuego during his voyage on HMS Beagle in 1832.
About this Species
Darwin’s fungus belongs to a genus of highly evolved parasitic fungi that grow exclusively on species of Nothofagus (southern beech). Thus, all Cyttaria species naturally occur in the southern hemisphere. Darwin’s fungus occurs only in South America, and is not known from Nothofagus in New Zealand or Australia. It was collected by Charles Darwin in Tierra del Fuego during the voyage of HMS Beagle in 1832, and was named in his honour when the species was scientifically described by Rev. Miles J. Berkeley in 1842.
Fruitbodies (actually stromata encompassing numerous fertile areas) develop from spring to early summer on galls, usually conspicuous swellings of the host trunk and branches which may reach at least 30 cm across. Fruitbodies can be produced in large quantities, falling to the ground at maturity, usually after discharge of the spores. The galls that the species induces are perennial, but the fungus does not cause wood decay and, though sometimes killing heavily infected branches, appears to have no serious effects on the long-term health of the host tree. Whether this is a true parasite has not been established, and a possible mutualism (whereby there is also some benefit to the tree from the presence of the fungus) has been suggested.
The fruitbodies are a food source to other animals, and are frequently colonised by the larvae of fungus gnats (Mycetophilidae).
Geography & Distribution
Cyttaria darwinii is known only from South America, including Argentina (it was originally found in Tierra del Fuego) and Chile. It grows on species of Nothofagus (southern beech), especially N. antarctica and N. pumilio, and occasionally on N. betuloides and N. dombeyi, to an altitude of 1700 m. Its distribution is restricted to that of its host trees, as it can only survive on Nothofagus species. Cyttaria species are not known to have become established with the host trees when these are grown elsewhere.
The bright yellow or orange-yellow fruitbodies of Darwin’s fungus appear on the branches and trunks of southern beech trees, where they often occur in conspicuous clusters that can be easily spotted from a distance. The spherical fruitbodies have a pitted surface on maturity and, in size and shape, individual fruitbodies bear a considerable resemblance to golf balls!
The stromata (masses of fungal tissue in which the fruitbody develops) are pale yellowish when young, later becoming bright yellow or orange-yellow. They are spherical and 2 to 5 cm wide, and may be developed singly or more usually in clusters on conspicuous swellings of living trunks and branches of southern beech (Nothofagus spp).
The young fruitbodies are smooth and firm, later developing numerous fertile pits, each 4 to 6 mm across. These pits are initially visible as pale areas on the stroma surface, but open at maturity and can be exposed by peeling off the surface layer. The hymenial surface (spore-bearing layer) is egg-yellow. The asci (cells in which ascospores are produced) are eight-spored, cylindric and tapered at the base with a ring at the tip showing as strongly blue in iodine. The ascospores are rounded, pale brown and smooth.
The development and structure of the fruitbodies of the related C. gunnii, an Australian species, are described in detail by White (1954).
Cyttaria darwinii (and some other Cyttaria species) can also exist in an asexual state, in which tiny asexual spores are produced at the base of the stromata.
Discovery and descriptionMore Information
Although already known to European sailors in the 18th century and commented on by other botanists, it was Charles Darwin who first collected material of this fungus for scientific study. He noted its abundance in the region and the way it was used by the local people. Darwin’s material was sent to the great British mycologist Rev. Miles J. Berkeley, who scientifically named the fungus a decade after its collection, in 1842. Darwin’s original collection, now preserved in the Mycology Herbarium at Kew, thus became the type material for this species.
Fruitbodies of C. darwinii collected in 1886 by Robert Cunningham during the Voyage of HMS Nassau, from Punta Arenas (Sandy Point) in Patagonia, are also at Kew, preserved in spirit and still maintained in one of the early glass containers. In the same paper as he described C. darwinii, Berkeley also described a Chilean species, C. berteroi, named for its collector, the Italian biologist Carlo Giuseppe Bertero, who was perhaps the first to realise that the Cyttaria stromata were not fruits of the tree but actually parasitic fungi. Yet another of the South American species of this genus was named by Berkeley in 1847 in honour of one of Kew’s directors Joseph Hooker: Cyttaria hookeri.
Threats & Conservation
Cyttaria darwinii specimen (Image: RBG Kew)
As the fungus can only survive with its host trees, the conservation of southern beech forests in South America is important for this and other species of Cyttaria. However, there is no evidence that the species is endangered. Darwin noted it “grows in vast numbers on the beech trees”. It remains widely used locally and appears still to be common. Nevertheless, it is one of six Cyttaria species (Cyttaria berteroi, C. darwinii, C. espinosae, C. exigua, C. hookeri, C. johowii) proposed for assessment of their conservation status under the IUCN Sampled Index Project, Ascomycete Conservation Specialist Group. In addition, the preservation of Cyttaria spp. as a food resource is linked to the protection of the temperate Nothofagus forests.
The fungus has traditionally been used for food, and is still a valuable food item. Its importance in this respect was already known to Charles Darwin who discussed it in ‘The Voyage of the Beagle’ published in 1839. He wrote: “In Tierra del Fuego the fungus in its tough and mature state is collected in large quantities by the women and children, and is eaten un-cooked. It has a mucilaginous, slightly sweet taste, with a faint smell like that of a mushroom. With the exception of a few berries, chiefly of a dwarf arbutus, the natives eat no vegetable food besides this fungus.” Indeed, from the 1760s onwards, sailing ships used the fruitbodies as food supplements.
Modern study has shown that edible Cyttaria species have a nutritional value similar to that of cultivated mushrooms and that, furthermore, they are beneficial to the consumer in improving the immune system.
In addition to the direct use of the fruitbodies, the galled host wood is used to make decorative products for local use and for the tourist trade.
Darwin's fungus at Kew
Cyttaria are southern hemisphere fungi and do not occur in Britain, although various Nothofagus species are grown in the Gardens. However, original material of C. darwinii collected by Charles Darwin, as well as collections of other Cyttaria species from throughout their range, are preserved in the Kew Mycology Herbarium. These are available to bona fide research workers by prior appointment, but there is no general public access.
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