perisztoma

Perisztoma, in bryology, refers to the peristome—the ring of toothlike structures around the opening of the moss capsule (sporophyte sporangium). It forms after the operculum (lid) falls away and plays a key role in controlling spore release. The peristome is exposed to ambient conditions and its movement helps regulate when spores are released, often in response to humidity and air movement.

Structure varies across moss groups. In haplolepidous peristomes, a single ring of 16 to 32 teeth surrounds the mouth. In diplolepidous peristomes, two concentric rings of teeth are present, typically with an inner membrane or endostome that can interact with the outer teeth. The teeth are hygroscopic, bending outward when dry to expose the opening and closing when moist to retain spores. The exact arrangement and presence of an endostome provide important taxonomic characters for identifying moss taxa.

Function and significance. The peristome enables gradual, wind-assisted spore dispersal, enhancing the likelihood of colonization in suitable microhabitats. Because its morphology—number and arrangement of teeth, presence of an endostome, and degree of reduction—varies among species, the peristome is a valuable feature in moss classification and phylogeny. In some moss lineages, the peristome is reduced or absent, reflecting ecological or evolutionary changes.

In summary, the perisztoma/peristome is a specialized, humidity-responsive structure at the moss capsule mouth essential for timing and efficiency of spore dispersal and for taxonomic differentiation within Bryophyta.