Cyathus is a genus of fungi in the Nidulariaceae, which is a family collectively known as the bird's nest fungi. They are given this name as they resemble tiny bird's nests filled with "eggs"structures large enough to have been mistaken in the past for seeds. However, these are now known to be reproductive structures containing spores. The "eggs", or peridioles, are firmly attached to the inner surface of this fruit body by an elastic cord of mycelia known as a funiculus. The 45 species are widely distributed throughout the world and some are found in most countries, although a few exist in only one or two locales. Cyathus stercoreus is considered endangered in a number of European countries. Some species of Cyathus are also known as splash cups, which refers to the fact that falling raindrops can knock the peridioles out of the open-cup fruit body. The internal and external surfaces of this cup may be ridged longitudinally (referred to as plicate or striate); this is one example of a taxonomic characteristic that has traditionally served to distinguish between species.
Generally considered inedible, Cyathus species are saprobic, since they obtain nutrients from decomposing organic matter. They usually grow on decaying wood or woody debris, on cow and horse dung, or directly on humus-rich soil. The life cycle of this genus allows it to reproduce both sexually, with meiosis, and asexually via spores. Several Cyathus species produce bioactive compounds, some with medicinal properties, and several lignin-degrading enzymes from the genus may be useful in bioremediation and agriculture. Phylogenetic analysis is providing new insights into the evolutionary relationships between the various species in Cyathus, and has cast doubt on the validity of the older classification systems that are based on traditional taxonomic characteristics.
Taxonomy
History Bird's nest fungi were first mentioned by Flemish botanist Carolus Clusius in (1601). Over the next couple of centuries, these fungi were the subject of some controversy regarding whether the peridioles were seeds, and the mechanism by which they were dispersed in nature. For example, the French botanist Jean-Jacques Paulet, in his work (1790–1793), proposed the erroneous notion that peridioles were ejected from the fruit bodies by some sort of spring mechanism.Brodie (1975), p. 15. The genus was established in 1768 by the Swiss scientist Albrecht von Haller; the generic name is Latin, but it was originally derived from the Ancient Greek word , meaning 'cup'. The structure and biology of the genus Cyathus was better known by the mid-19th century, starting with the appearance in 1842 of a paper by Carl Johann Friedrich Schmitz, and two years later, a monograph by the brothers Louis René and Charles Tulasne. The work of the Tulasnes was thorough and accurate, and was highly regarded by later researchers. Subsequently, monographs were written in 1902 by Violet S. White (on American species), Curtis Gates Lloyd in 1906, Gordon Herriot Cunningham in 1924 (on New Zealand species), and Harold J. Brodie in 1975.Brodie, The Bird's Nest Fungi.
Infrageneric classification The genus Cyathus was first subdivided into two infrageneric groups (i.e., grouping species below the rank of genus) by the Tulasne brothers; the "eucyathus" group had fruit bodies with inner surfaces folded into pleats (plications), while the "olla" group lacked plications. Later (1906), Lloyd published a different concept of infrageneric grouping in Cyathus, describing five groups, two in the eucyathus group and five in the olla group.
In the 1970s, Brodie, in his monograph on bird's nest fungi, separated the genus Cyathus into seven related groups based on a number of taxonomic characteristics, including the presence or absence of plications, the structure of the peridioles, the color of the fruit bodies, and the nature of the hairs on the outer peridium:Brodie (1975) pp. 150–80.
Olla group: Species with a tomentum having fine flattened-down hairs, and no plications. C. olla, C. africanus, C. badius, C. canna, C. colensoi, C. confusus, C. earlei, C. hookeri, C. microsporus, C. minimus, C. pygmaeus Pallidus group: Species with conspicuous, long, downward-pointing hairs, and a smooth (non-plicate) inner peridium. C. pallidus, C. julietae Triplex group: Species with mostly dark-colored peridia, and a silvery white inner surface. C. triplex, C. setosus, C. sinensis Gracilis group: Species with tomentum hairs clumped into tufts or mounds. C. gracilis, C. intermedius, C. crassimurus, C. elmeri Stercoreus group: Species with non-plicate peridia, shaggy or wooly outer peridium walls, and dark to black peridioles. C. stercoreus, C. pictus, C. fimicola Poeppigii group: Species with plicate internal peridial walls, hairy to shaggy outer walls, dark to black peridioles, and large, roughly spherical or ellipsoidal spores. C. poeppigii, C. crispus, C. limbatus, C. gayanus, C. costatus, C. cheliensis, C. olivaceo-brunneus Striatus group: Species with plicate internal peridia, hairy to shaggy outer peridia, and mostly elliptical spores. C. striatus, C. annulatus, C. berkeleyanus, C. bulleri, C. chevalieri, C. ellipsoideus, C. helenae, C. montagnei, C. nigro-albus, C. novae-zeelandiae, C. pullus, C. rudis
Phylogeny The 2007 publication of phylogenetic analyses of DNA sequence data of numerous Cyathus species has cast doubt on the validity of the morphology-based infrageneric classifications described by Brodie. This research suggests that Cyathus species can be grouped into three genetically related clades:
Ollum group: C. africanus (type), C. africanus f. latisporus, C. conlensoi, C. griseocarpus, C. guandishanensis, C. hookeri, C. jiayuguanensis, C. olla, C. olla f. anglicus, and C. olla f. brodiensis. Striatum group: C. annulatus, C. crassimurus, C. helenae, C. poeppigii, C. renwei, C. setosus, C. stercoreus, and C. triplex. Pallidum group: C. berkeleyanus, C. olla f. lanatus, C. gansuensis, and C. pallidus.
This analysis shows that rather than fruit body structure, spore size is generally a more reliable character for segregating species groups in Cyathus. For example, species in the ollum clade all have spore lengths less than 15 μm, while all members of the pallidum group have lengths greater than 15 μm; the striatum group, however, cannot be distinguished from the pallidum group by spore size alone. Two characteristics are most suited for distinguishing members of the ollum group from the pallidum group: the thickness of the hair layer on the peridium surface, and the outline of the fruit bodies. The tomentum of Pallidum species is thick, like felt, and typically aggregates into clumps of shaggy or woolly hair. Their crucible-shaped fruit bodies do not have a clearly differentiated stipe. The exoperidium of Ollum species, in comparison, has a thin tomentum of fine hairs; fruit bodies are funnel-shaped and have either a constricted base or a distinct stipe.
Description Species in the genus Cyathus have fruit bodies (peridia) that are vase-, trumpet- or urn-shaped with dimensions of wide by tall. Fruit bodies are brown to gray-brown in color, and covered with small hair-like structures on the outer surface. Some species, like C. striatus and C. setosus, have conspicuous bristles called setae on the rim of the cup. The fruit body is often expanded at the base into a solid rounded mass of hyphae called an emplacement, which typically becomes tangled and entwined with small fragments of the underlying growing surface, improving its stability and helping it from being knocked over by rain.Brodie (1975), pp. 5–7. Immature fruit bodies have a whitish membrane, an epiphragm, that covers the peridium opening when young, but eventually dehisces, breaking open during maturation. Viewed with a microscope, the peridium of Cyathus species is made of three distinct layers—the endo-, meso-, and ectoperidium, referring to the inner, middle, and outer layers respectively. While the surface of the ectoperidium in Cyathus is usually hairy, the endoperidial surface is smooth, and depending on the species, may have longitudinal grooves (striations).
Because the basic fruit body structure in all genera of the family Nidulariaceae is essentially similar, Cyathus may be readily confused with species of Nidula or Crucibulum, especially older, weathered specimens of Cyathus that may have the hairy ectoperidium worn off.Brodie (1975), p. 147. It distinguished from Nidula by the presence of a funiculus, a cord of hyphae attaching the peridiole to the endoperidium. Cyathus differs from genus Crucibulum by having a distinct three-layered wall and a more intricate funiculus.
Peridiole structure
Derived from the Greek word peridion, meaning "small leather pouch",Alexopolous et al. (1996), p. 545. the peridiole is the "egg" of the bird's nest. It is a mass of basidiospores and glebal tissue enclosed by a hard and waxy outer shell. The shape may be described as lenticular—like a biconvex lens—and depending on the species, may range in color from whitish to grayish to black. The interior chamber of the peridiole contains a hymenium that is made of basidia, sterile (non-reproductive) structures, and spores. In young, freshly opened fruit bodies, the peridioles lie in a clear gelatinous substance which soon dries.Brodie (1975), p. 6.
Peridioles are attached to the fruit body by a funiculus, a complex structure of hyphae that may be differentiated into three regions: the basal piece, which attaches it to the inner wall of the peridium, the middle piece, and an upper sheath, called the purse, connected to the lower surface of the peridiole. In the purse and middle piece is a coiled thread of interwoven hyphae called the funicular cord, attached at one end to the peridiole and at the other end to an entangled mass of hyphae called the hapteron. In some species the peridioles may be covered by a tunica, a thin white membrane (particularly evident in C. striatus and C. crassimurus).Brodie (1975), p. 129. Spores typically have an elliptical or roughly spherical shape, and are thick-walled, hyaline or light yellow-brown in color, with dimensions of 5–15 by 5–8 μm.
Life cycle The life cycle of the genus Cyathus, which contains both haploid and diploid stages, is typical of taxa in the basidiomycetes that can reproduce both asexually (via vegetative spores), or sexually (with meiosis). Like other wood-decay fungi, this life cycle may be considered as two functionally different phases: the vegetative stage for the spread of mycelia, and the reproductive stage for the establishment of spore-producing structures, the fruit bodies.
The vegetative stage encompasses those phases of the life cycle involved with the germination, spread, and survival of the mycelium. Spores germinate under suitable conditions of moisture and temperature, and grow into branching filaments called hyphae, pushing out like roots into the rotting wood. These hyphae are homokaryotic, containing a single nucleus in each compartment; they increase in length by adding cell-wall material to a growing tip. As these tips expand and spread to produce new growing points, a network called the mycelium develops. Mycelial growth occurs by mitosis and the synthesis of hyphal biomass. When two homokaryotic hyphae of different mating compatibility groups fuse with one another, they form a dikaryotic mycelia in a process called plasmogamy. Prerequisites for mycelial survival and colonization a substrate (like rotting wood) include suitable humidity and nutrient availability. The majority of Cyathus species are saprobic, so mycelial growth in rotting wood is made possible by the secretion of enzymes that break down complex polysaccharides (such as cellulose and lignin) into simple sugars that can be used as nutrients.Deacon (2005), pp. 231–4.