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.

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.

For example, the French botanist Jean-Jacques Paulet, in his work Traité des champignons (1790–1793), proposed the erroneous notion that peridioles were ejected from the fruit bodies by some sort of spring mechanism.

[2] The genus was established in 1768 by the Swiss scientist Albrecht von Haller; the generic name Cyathus is Latin, but it was originally derived from the Ancient Greek word κύαθος, meaning 'cup'.

[3] 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,[4] and two years later, a monograph by the brothers Louis René and Charles Tulasne.

[7] 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:[10] 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.

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.

Species in the genus Cyathus have fruit bodies (peridia) that are vase-, trumpet- or urn-shaped with dimensions of 4–8 millimetres (3⁄16–5⁄16 inch) wide by 7–18 mm (1⁄4–11⁄16 in) tall.

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.

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.

[12] 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).

Spores germinate under suitable conditions of moisture and temperature, and grow into branching filaments called hyphae, pushing out like roots into the rotting wood.

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.

[22] Lu suggested in 1965 that certain growing conditions—such as a shortage in available nutrients—shifts the fungus' metabolism to produce a hypothetical "photoreceptive precursor" that enables the growth of the fruit bodies to be stimulated and affected by light.

[28][33] Cyathane diterpenoids also stimulate nerve growth factor synthesis, and have the potential to be developed into therapeutic agents for neurodegenerative disorders such as Alzheimer's disease.

[40] Examples of the ability of Cyathus to thrive in somewhat inhospitable environments are provided by C. striatus and C. stercoreus, which can survive the drought and cold of winter in temperate North America,[41] and the species C. helenae, which has been found growing on dead alpine plants at an altitude of 2,100 metres (7,000 ft).

[48] The discovery of a Cyathus species in Dominican amber (C. dominicanus) suggests that the basic form of the bird's nest fungi had already evolved by the Cretaceous era and that the group had diversified by the mid-Cenozoic.

The fruit body is shaped so that the kinetic energy of a fallen raindrop is redirected upward and slightly outward by the angle of the cup wall, which is consistently 70–75° with the horizontal.

[50] The action ejects the peridioles out of the so-called "splash cup", where it may break and spread the spores within, or be eaten and dispersed by animals after passing through the digestive tract.

In the genus Cyathus, as a peridiole is jerked out of its cup, the funiculus is torn and this makes possible the expansion of a mass of adhesive hyphae (the hapteron) which clings to any object in the line of flight.

[53]Although it has not been shown experimentally if the spores can survive the passage through an animal's digestive tract, the regular presence of Cyathus on cow or horse manure strongly suggest that this is true.

[55] Species in the family Nidulariaceae, including Cyathus, are considered inedible, as (in Brodie's words) they are "not sufficiently large, fleshy, or odorous to be of interest to humans as food".

[65] Extracts of C. striatus have inhibitory effects on NF-κB, a transcription factor responsible for regulating the expression of several genes involved in the immune system, inflammation, and cell death.