the cushion moss of NZ's exposed rock faces and walls
- Size
- Height: 1–3 cm
- Lifespan
- 5–15 years
- Diet
- Grows on rocks, stone walls, and boulders in exposed, sunny locations. Requires stable rock surfaces, good light, and well-drained conditions. Tolerates sun, wind, drought, and extreme temperatures.
- Habitat
- Grows on rocks, stone walls, and boulders in exposed, sunny locations. Forms small, dense, grey-green cushions that grip the rock tightly.
- Range
- Found throughout the North and South Islands on rocks, stone walls, and boulders in exposed, sunny locations. Most common in the South Island's high country and the North Island's volcanic plateau. Also found in temperate regions worldwide.
- Endemism
- Native
- Main Threats
- None significant. This species is common and widespread on rocks and stone walls. Localised threats include quarrying of rock outcrops, removal of stone walls, and climate change affecting rock surface moisture.
- Population
- Not Threatened. Grimmia rock moss is common on rocks, stone walls, and boulders throughout New Zealand. It is a widespread species found in temperate regions around the world.
- Conservation Status
- Not Threatened
The one that looks like it is holding on for dear life has stems that are short and densely packed, forming small, rounded, grey-green cushions on the rock. The leaves are narrow and pointed, with a long, white, hair-like tip (awn) that extends beyond the leaf tip. These white tips give the cushions a hoary, frosted appearance, like they have been dusted with snow. When the moss is dry, the leaves curl inward, and the cushions shrink and turn dark. When it is wet, the leaves unfurl, and the cushions expand and turn bright green. It is the moss of the tight grip, the one that holds onto the rock like it is the last stable thing.
What makes it special is the grip. Grimmia rock moss is one of the most tenacious mosses in New Zealand. It grows on bare rock, on vertical stone walls, on the tops of boulders, places where there is no soil, no organic matter, nothing but hard stone. It holds on with its rhizoids, root-like structures that penetrate the microscopic pores of the rock, anchoring it firmly. You can try to scrape it off, and you will fail. It is the moss of the stone, the one that grips like it will never let go, the one that has learned to thrive where nothing else can.
The leaves are narrow and pointed, with a long, white, hair-like tip. The leaf margins are recurved (curled under), and the leaf surface is smooth. The white tips reflect sunlight, protecting the moss from drying out. Under a hand lens, the white tips are beautiful, each one a tiny glassy thread extending from the leaf.
Biologically, the grimmia rock moss reproduces by spores, released from capsules on short stalks. The capsules are hidden among the leaves, often hard to see. The spores are tiny, carried by the wind to new rocks.
To find grimmia rock moss is to find the small, grey-green cushions on the rock. They grip tightly, bristling with white hair-like tips. You can try to scrape them off, and you will see how they hold on. It is the moss of the tight grip, the one that holds onto the rock like it is the last stable thing, the one that proves that the most successful strategy is sometimes just to hold on and never let go.