the rosette lichen of NZ's bark and old fence posts
- Size
- Width: 5–15 cm
- Lifespan
- 10–50 years
- Diet
- Grows on bark of trees, rocks, and fence posts in open, sunny locations. Requires clean air, stable bark or rock surfaces, and good light. Tolerates sun, wind, and moderate drought.
- Habitat
- Grows on the bark of trees, on rocks, and occasionally on old fence posts throughout New Zealand. A creature of the branch and the boulder, the forest and the garden. Found from sea level to the montane zone, particularly in open, sunny locations where the bark is rough and the air is clean. The lichen of the pale green, the one that looks sunlit even in the shade.
- Range
- Found throughout the North and South Islands on bark of native and introduced trees, rocks, and fence posts in open, sunny locations. Most common in the North Island and the northern South Island. Also found in temperate and subtropical regions worldwide.
- Endemism
- Native
- Main Threats
- None significant. This species is one of the most common lichens in New Zealand. Localised threats include air pollution, removal of old trees, and bark disturbance. Classified as Not Threatened, with healthy populations on bark of trees throughout New Zealand in clean-air areas.
- Population
- Not Threatened. This is a common and widespread lichen in New Zealand, particularly in the North Island and the northern South Island. It grows on the bark of native and introduced trees, on rocks, and on fence posts.
- Conservation Status
- Not Threatened
The one that looks like it is glowing has a body that is flat, leafy, and pale green, a distinctive yellowish-green or apple-green that stands out against the grey bark. The lobes are broad and rounded, spreading across the trunk like a map of a foreign country. The surface is smooth and shiny, often covered in a network of fine, white lines. It is the lichen of the pale light, the one that looks like it is catching the sun even when the sun is not there.
What makes it special is the colour. The green shield lichen is one of the few lichens in New Zealand that is truly green. Most grey lichens have a hint of green, but this one is green, pale, bright, almost luminous. The colour comes from the alga that lives inside the lichen, a species of Trebouxia that is particularly efficient at capturing light. In the shade, the lichen turns a darker, olive green. In the sun, it fades to a pale, yellow-green. It is the chameleon of the green world, the one that changes with the light.
The surface of the lobes is smooth and shiny, often with a network of white, wavy lines. The margins are entire or slightly wavy, not frilly like the ragged parmelia. The underside is black and covered in a sparse mat of rhizines, tiny, root-like structures that anchor it to the bark. Under a hand lens, the white lines are visible, a delicate network on the green surface.
Biologically, the green shield lichen is a partnership, a fungus and an alga living together. The fungus provides structure and protection. The alga provides food through photosynthesis. The green shield lichen is particularly sensitive to air pollution. It is less common in cities and industrial areas. In clean air, it thrives. It is the canary of the bark, the one that tells us whether the air is healthy.
To find green shield lichen is to find the pale green patch on the bark. It is flat, leafy, and bright, a living glow on the tree. You can run your finger over the surface and feel the smooth, shiny texture. It is the lichen of the pale light, the one that looks sunlit even in the shade, the one that proves that even in the dark corners of the forest, there is a little bit of sun.