warts up on undisturbed tree bark slowly

Size
Width: 5–20 cm
Lifespan
20–100 years
Diet
Obtains nutrients via symbiotic partnership. Fungus provides structure. Alga provides photosynthetic food. Requires clean air and high humidity.
Habitat
Grows on bark of trees, rocks, and wood in damp, undisturbed forests. Forms thick, warty, pale grey crust that grows very slowly.
Range
Found throughout the North and South Islands on bark of native trees, rocks, and wood in damp, undisturbed forests. Most common in the South Island's beech forests and the North Island's western ranges. Also found in temperate regions worldwide.
Endemism
Native
Main Threats
None significant. This species is common and widespread in damp, undisturbed forests. Localised threats include forest clearance, air pollution, and removal of old trees with stable bark surfaces.
Population
Not Threatened. Pertusaria lichen is common and widespread in New Zealand, particularly on the bark of native trees in damp, undisturbed forests. It grows slowly and can persist for decades.
Conservation Status
Not Threatened
Human Risk
harmless
Handling Note
crustose lichen, safe to handle
Conservation Note
Native lichen; not assessed by NZTCS as lichens are generally outside the scope of current threat classifications.
Te Ao Māori
No recorded Māori name distinguishes the pertusaria lichen from other lichens. Lichens were generally called pūkohu (mosses and lichens) or pukorokoro (crustose lichens). The warted, lumpy crust on the old bark would have been noticed. It looked like the skin of an old tree. Like the marks of age. But no distinct name survives. The pertusaria lichen was sometimes used as a dye. The pale pigment could be extracted. It was used to colour fibres. Though it was not as vibrant as other lichens.
Without it, the bark is just wood. With it, there are warts. Pertusaria lichen looks like it has been sitting there forever. It has a body that is a thick, crusty layer. It grows on the surface of the bark or rock. Forming a pale greyish-white to off-white patch. The crust is rough and uneven. Covered in tiny, wart-like bumps (verrucae). These give it a lumpy, textured appearance. Scattered across the surface are small, pore-like openings (ostioles). Where the spores are released. It is the lichen of the warted surface. The one that looks like it has been there so long it has grown bumps. The one that seems to have absorbed the age of the tree. What makes it special is the stubbornness. Pertusaria lichen is one of the slowest-growing lichens in New Zealand. It adds only a fraction of a millimetre per year. Creeping across the bark at a pace that is almost impossible to measure. A patch the size of your palm may be a century old. It is the lichen of the patient one. The one that takes its time. And does not care how long it takes. The one that outlasts the trees it grows on. The pertusaria lichen is a crustose lichen. It grows flat on the bark or rock. Like a crust of paint. Rather than upright or leafy. Its body is a thick, warted crust. Often forming circular patches or irregular stains. The verrucae are the fruiting structures. Embedded in the crust. With tiny pores at the top. Under a hand lens, the verrucae are visible. Tiny bumps on the surface of the crust. Biologically, the pertusaria lichen is a partnership. A fungus and an alga live together. The fungus provides structure and protection. The alga provides food through photosynthesis. The ostioles are the openings of the fruiting bodies. Releasing spores into the air. To find pertusaria lichen is to find the warted patch on the old bark. It is pale, lumpy, and stubborn. A living fossil on the tree. You can run your finger over the surface. Feel the bumps. The warts. The texture of age. It is the lichen of the warted surface. The one with a stubborn, slow-growing presence. The one that proves that patience is a form of strength.