Lichen
Lichenes
Lichens are slow-growing colonies of algae and fungi that form crusty, leafy or fluffy patches on thinning turf, mulch, pots and plant bark.
Lichen is not a single plant or weed species but a symbiotic association between a fungus and an alga (or cyanobacterium). The fungal partner provides structure and the alga or cyanobacterium provides food through photosynthesis. Together they form a self-supporting organism that grows very slowly on surfaces rather than rooting into them.
Lichens take several growth forms. Crustose lichens are flat, crust-like patches tightly fused to the surface, often grey, green-grey, yellow or orange. Foliose lichens have leafy, lobed structures that lift slightly at the edges. Fruticose lichens are shrubby or hair-like, forming tufted or branching growths. On turf, crustose and foliose types are most common, appearing as grey-green to black scaly or gelatinous patches sitting on top of the soil or thatch surface, not attached to grass plants themselves.
In nursery and landscape settings, lichen commonly colonises pot surfaces, garden edging, mulch, retaining walls, tree bark and rocks. In turf it establishes in thin, weak or compacted areas where grass cover is sparse and light reaches the soil surface. It is widespread across Australia and can be found year-round, but growth is most active during cool, moist periods in autumn, winter and spring, slowing during hot, dry conditions.
Lichen itself does not parasitise plants and is not directly pathogenic. Its presence is a symptom of poor turf density, low fertility, compaction, excessive shade, poor drainage or old, worn surfaces such as ageing mulch or bark. Management focuses on correcting these underlying conditions rather than treating the lichen as a disease, since improving turf vigour and surface conditions will naturally reduce lichen cover over time.
How to identify
- Patchy crusty or leafy growth: grey-green, black, yellow or orange patches sitting on the soil surface, thatch, mulch, bark, pots or pavers rather than growing from within the plant.
- Associated turf thinning: lichen patches usually coincide with areas of sparse, weak or slow-growing turf, often linked to compaction, shade, poor drainage or low fertility.
- Texture varies by type: crustose lichen feels flat and crusty when dry, and can become slippery or gelatinous when wet; foliose types have small leaf-like lobes; fruticose types look tufted or hair-like.
- Field check: lichen is not rooted into the plant or soil — it can usually be scraped or peeled off the surface intact, unlike moss, which has fine rhizoids anchoring it, or algae, which forms a slimy, structureless film rather than a defined patch.
- Lookalikes: moss forms soft, green, upright or mat-like growth with fine leafy stems and can be pulled up in a mat; algae forms a slick, dark green to black slime layer with no defined structure. Lichen is firmer, dry-textured when not wet, and often multi-coloured (grey, orange, yellow patches) rather than uniformly green.
