Spore Dispersal
Like other bird's nest fungi in the Nidulariaceae, species of Cyathus have their spores dispersed when water falls into the fruit body. 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. 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. This method of spore dispersal in the Nidulariaceae was tested experimentally by George Willard Martin in 1924, and later elaborated by Arthur Henry Reginald Buller, who used Cyathus striatus as the model species to experimentally investigate the phenomenon. Buller's major conclusions about spore dispersal were later summarized by his graduate student Harold J. Brodie, with whom he conducted several of these splash cup experiments:
Raindrops cause the peridioles of the Nidulariaceae to be thrown about four feet by splash action. 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. The momentum of the peridiole causes a long cord to be pulled out of a sheath attached to the peridiole. The peridiole is checked in flight and the jerk causes the funicular cord to become wound around stems or entangled among plant hairs. Thus the peridiole becomes attached to vegetation and may be eaten subsequently by herbivorous animals.
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. Alternatively, the hard outer casing of peridioles ejected from splash cups may simply disintegrate over time, eventually releasing the spores within.
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