Cyttaria darwinii is a member of the genus Cyttaria, and grows abundantly as a parasite on the Southern Beech, Nothofagus. Darwin first collected them in his voyage to the Patagonia on the Beagle. The fruiting bodies, or reproductive structures, of C. darwinii are vivid orange or whitish globes, described by Darwin as “the colour of the yolk of an egg”, with varying sizes “from that of a bullet to that of a small apple”. He compares the gelatinous interior to “vermicelli pudding”. They grow from the host beech in groups off of stems. These golf ball-like fruiting bodies have mucous-like fluid inside that dries as the balls age. In the Tierra del Fuego, they are commonly used as food.
The description of the genus Cyttaria was first published in the Transactions of the Linnaean Society, Volume 19, in 1841. Because of Cyttaria’s close relationship to its host and the remarkable geographic distribution of Nothofagus, this genus is of particular interest as a system to study host-parasite relationships in a biogeographic framework.
Nothofagus, the host plant of Cyttaria, is widespread throughout the Southern hemisphere, with extant species in South America, Australia, New Zealand, New Guinea, New Caledonia, and evidence of an extinct species in Antarctica. This distribution is now believed to be a result of dispersal that occurred after the Gondwanan breakup.
Seven groups within Cyttaria are found only in Southern South America, and five groups are found only in Southeastern Australasia and New Zealand. Species are not found in common between South America and Australasia, and none at all are found on New Caledonia and New Guinea, despite the presence of its host.
The distribution of Australasian and South American Nothofagus is thought to be caused by vicariant events in geologic history that caused an ancestral distribution to divide as the continents moved. The divergence of Cyttaria species in Australia and in South America matched those of their hosts.
Unlike the majority of fungi, all Cyttaria lack chitin in their cell walls. They, instead, have β-1–3-glucan.
The fruiting bodies are supported by brown stems with a granulated texture. The outside surface of the fruiting body is tough, smooth and shiny, and a mass of brown fibres protrudes from the stem. Holes pit the surface of the fruiting bodies, bearing the hymenium, or the surface bearing reproductive spores. The hymenium bears a fleshy jelly-like layer, the compound stroma, where apothecia, or cup-like spore-bearing structures, form underneath a membrane that encloses the entire fruit body. This membrane, called the ectostroma, ruptures and peels away when the fruiting body reaches maturity, leaving a pockmarked globose body that resembles a golf ball. The compound stroma are formed by the fusion of simple stromata with one apothecium each. Each stroma has between one and two hundred apothecia. The stromata grow from woody and hyphal spines that protrude from the woody host. As the stroma grows, it becomes spherical and rubbery, with a toughened cortical layer. Beneath this layer, the apothecia form, stretching out the cortical layer and rupturing it upon reaching maturity. The central part of the stroma is called the medulla, which is a mass of hyphae with cartilaginous fibres . These fibres form the point of attachment to the host. The external layer of the stroma may be perforated between apothecia. Once the apothecia are fully formed, the gelatinous interior of the globose fruiting bodies goes away.
The asci are inoperculate and have apices of the Bulgaria inquinans type. The paraphyses, or structures that are found between asci in the apothecium, are branched, expanded at the tip, and colourful. The annulus, or the ring of remainder from the ectostroma, is stained blue by iodine. The dark grey or black ascospores, of which there are eight per ascus, are uninucleate and roughly globose, and can be smooth or finely wrinkled. The spores, which measure roughly 12 microns in diameter, and are actively discharged from the asci in a cloud.
The galls that Cyttaria forms are perennial, and they produce annual crops of new stromata, or the gelatinous spore-bearing layers. Cyttaria species are morphologically separated using gall type, relative sizes of branches and galls, and shapes of woody tissue protrusion under the bark. C. darwinii’s galls are globose, with the mycelium, or vegetative growth of the fungus, remaining mostly at the site of local infection in the host tree. In C. darwinii, some fibrous growths poke through the skin of the fruiting bodies.
Within the genus Cyttaria, C. darwinii and C. exigua are sisters in a monophyletic group, with the distinguishing character of very thick ectostroma, separated apothecia, and basal characteristics of the spermogonia.
On a larger scale, the Cyttaria can be divided into three clades within the genus, one of which parasitizes the subgenus Nothofagus which is exclusive to South America, one of which parasitizes both Nothofagus and Lophozonia but also exclusively in South America, and one of which parasitizes Lophozonia and is found trans-Antarctically.
All twelve species of Cyttaria form obligate biotrophic associations with all eleven species of two out of the four subgenera of Nothofagus: Lophozonia and Nothofagus. While the numbers match up, there is no strict one-to-one relationship between the parasite and host – more than one species of Cyttaria can parasitize the same species of Nothofagus, and more than one beech species can serve has host to a single species of the parasite. Each clade within the Cyttaria genus grows on only one subgenus of Nothofagus.These subgenera of Nothofagus that host Cyttaria are not particularly closely related within the genus, and the other two subgenera do not host Cyttaria at all. Cyttaria darwinii is found on Nothofagus dombeyi, N. pumilio, N. antarctica, and N. betuloides.
Parasites of the entire genus attack their hosts by invading new plant growth with hyphal growth from germinating spores. The host’s growth is controlled by intracellular invasion by the parasite. The parasite causes large gelatinous galls, or surface growths, to form on the tree. The tree’s branch growth slows, and the ends of branches can even fall off, as small branches are shed along with its galls to prevent the fungus from establishing. Infected trees die through suppression, or inhibition of growth, which affects the ecosystem at large. Invasion by Cyttaria has been cited as the greatest factor inhibiting growth of forests of Nothofagus menziensii in New Zealand. The galls grow mostly on heavily branched trees at the boundaries of forests and in open clearings, because in these environments, branches are not shed as regularly as they are in more dense stands of trees.
Relevance to Humans and Ecosystems
In the Journal of Researches, Darwin remarked that the Araucarian Indians of the Tierra del Fuego ate the mature fruiting body of Cyttaria darwinii uncooked, often with fish. He describes the young Cyttaria as tasteless. More mature, strongly-smelling, sweet-tasting fruiting bodies formed a main part of the Fuegian diet, and was the only “vegetable” that they ate, according to Darwin. Later researchers reported that C. gunii, C. hookerii, and C. harioti were also eaten in that region. While Cyttaria in Patagonia were often infested with larvae, they tended to be less so in the Chilean hills near Nancagua and San Fernando, where they were also eaten. The Mapuche collected several varieties, called dihuene, diguene, quirene, pna, pinatra, and curacucha. The parasite was considered the fruits of the host trees themselves. C. darwinii in particular was used as food by the Selknam, Kawashkar, and Yamana also from the Tierra del Fuego.
Cyttaria is still gathered today, serving as extra income for agrarian communities in Southern Chile, who sell them in city markets. Consisting of 14 to 22% protein by dry weight, C. darwinii is the most nutritious of its genus and therefore is the most collected. Non-timber forest products, including fungi, are important for subsistence in these communities in the Chilean temperate forests. These forests are are threatened by practices of producing wood chips from local trees and introducing nonnative species of trees, especially from the groups Pinus and Eucalyptus. Conservation of the native Chilean temperate forests is a necessity, not only for protecting biodiversity, but also the livelihood of local people.