Tortula cernua

Tortula cernua is characterised by its distinctive leaf and reproductive structures. The leaves are elliptical in shape, with tips that range from broadly pointed to rounded, often ending in a small point or sharp projection. The leaf margins curl under in the middle portion and are bordered by 2–3 rows of specialised cells that are narrower and more rectangular than the surrounding tissue. These border cells have thicker walls and can be layered in one or two levels. Running through the centre of each leaf is a prominent vein (costa) that either reaches the tip or extends slightly beyond it. The vein is notably narrow near the tip, showing 3–4 cells across its curved upper surface. The cells of the leaf blade (lamina) near the tip are either hexagonal or rectangular in shape, measuring about 16–24 micrometres (μm) in width (though ranging from 13–28), and are typically smooth or rarely showing very slight surface bumps. The species is autoicous, meaning male and female reproductive structures occur on the same plant but in different locations. Field observations have documented a relationship between this moss and springtails (Collembola). In northern Norway, masses of the springtail species Xenylla humicola have been observed moving among the apical leaves of fertile shoots, apparently attracted by sex-specific volatile compounds produced by the plants. …

The species has a wide global distribution, occurring in North and South America, Europe, and Asia. In Europe, while it is found across the continent, records are typically sparse and isolated. In Switzerland, where it was last observed in 1942, it historically occurred in the eastern Central Alps and Ticino regions from hillside areas up to subalpine elevations at 200–1,500 m (660–4,920 ft). In these areas, it grew on old, damp walls and rocks, preferring calcareous stone substrates like mortar and clay, as well as sandy-loamy soils. In Britain, T. cernua is classified as endangered in the Bryophyte Red List and is protected under Schedule 8 of the Wildlife and Countryside Act 1981. The UK population is restricted to a small area spanning South Yorkshire, north Nottinghamshire and north-east Derbyshire. In these locations, the species grows specifically on fine lime waste with high pH values (typically between 8.7 and 9.2), primarily found as a by-product of historical lime kilns. This substrate has distinctive chemical properties that make it inhospitable to most other plant species: it contains concentrated levels of magnesium from the burning process, has a high magnesium:calcium ratio that limits potassium uptake in plants, and has severely limited phosphorus availability and very low iron content. …