The one that looks like it is holding on for dear life has stems that are short and upright, forming small, dense, greyish-green cushions on the surface of the stone. The leaves are narrow and pointed, with a distinctive, white, hair-like tip (awn) that extends beyond the leaf tip. When dry, the leaves curl and twist, giving the cushion a shaggy, unkempt appearance. When wet, they unfurl and turn bright green. It is the moss of the tight grip, the one that clings to stone like it is paying rent. What makes it special is the tenacity. Wall screw moss is one of the most tenacious mosses in New Zealand. It grows on vertical stone walls, on rooftops, on the sides of buildings, places where there is no soil, no organic matter, nothing but bare stone. It holds on with its rhizoids, root-like structures that penetrate the microscopic pores of the stone, anchoring it firmly. You can try to scrape it off, and you will fail. It is the moss of the stone, the one that pays its rent in persistence, the one that never lets go. The leaves are narrow and pointed, with a long, white, hair-like tip (awn) that reflects sunlight and traps moisture. The leaf surface is covered in tiny, papillose bumps that give it a rough, textured appearance. When dry, the leaves twist and curl, reducing water loss. Under a hand lens, the white awns are visible, tiny glassy threads extending from each leaf tip. Biologically, the wall screw moss reproduces by spores, released from capsules on tall stalks. The capsules are cylindrical and curved, with a long, twisted peristome (the screw that gives the moss its name). The spores are tiny, carried by the wind to new walls. To find wall screw moss is to find the greyish-green cushions on the old stone wall. They are small, dense, and clingy, a living payment on the stone. You can try to scrape it off, and you will see how it holds on. It is the moss of the tight grip, the one that clings to stone like it is paying rent, the one that proves that persistence pays off.