Syntrichia is a large, cosmopolitan genus of mosses in the family Pottiaceae, order Pottiales, placed within the class Bryopsida of the phylum Bryophyta. The genus contains approximately 114 accepted species according to the World Flora Online (2020) and has a worldwide distribution spanning every major continent and biome, from Arctic tundra and boreal forests to deserts, grasslands, and tropical regions.
Plants in the genus grow as cushions or tufts of erect stems, typically a few centimetres tall. The leaves are broadly tongue-shaped to lanceolate with a strong midrib (costa) that often extends beyond the leaf tip as a hair point. When hydrated, the plants are bright green and the leaves spread outward; when dry, the leaves contract and twist around the stem, giving the plants a reddish-brown appearance. This reversible desiccation response is one of the genus's most studied traits.
Syntrichia species are commonly found on calcareous soils, rock surfaces, walls, tree bark, and in cryptogamic soil crusts. They play an ecological role in stabilizing bare soil and reducing erosion, particularly in arid and semi-arid landscapes. Several species — most notably Syntrichia ruralis (twisted moss or star moss) — have become important model organisms in desiccation-tolerance research. These mosses can remain metabolically dormant for decades during drought and resume photosynthesis within two hours of rehydration.
The genus name is derived from Greek, combining "with" (syn-) and "hair" (trich-), referring to the distinctive twisted peristome teeth united by a basal membrane that characterize the group. Syntrichia was formerly treated under the broadly circumscribed genus Tortula, and many species are still encountered in older literature under that name.
Etymology
The name Syntrichia derives from Greek, combining syn- ("with") and trich- ("hair"), referring to the twisted peristome teeth that are united by a basal membrane — a defining morphological feature of the genus.
Distribution
Syntrichia has a cosmopolitan distribution, with species recorded across North America, Europe, Asia, the Middle East, Africa, South America, Australia, and the Pacific. Individual species occupy a wide range of habitats, from Arctic tundra and alpine zones to desert soils, temperate grasslands, and tropical regions, most commonly on calcareous substrates.
Ecology
Species of Syntrichia are pioneer colonizers of bare mineral soils, rock faces, walls, and tree bark. They are frequent components of cryptogamic soil crusts in arid and semi-arid regions, where they contribute to soil stabilization and erosion control. The genus is renowned for exceptional desiccation tolerance: plants can lose nearly all their water and remain dormant for many years, then resume full metabolic activity within hours of rehydration. Syntrichia ruralis has been extensively studied as a model organism for understanding this adaptation.
Taxonomy Notes
Syntrichia was historically treated as part of the broadly circumscribed genus Tortula (also in Pottiaceae), and many of its species circulate in older literature under Tortula names. Modern molecular and morphological studies have supported the segregation of Syntrichia as a distinct genus. The genus belongs to the family Pottiaceae within the order Pottiales (class Bryopsida, phylum Bryophyta).
