upper cortex
thallus structure
Quick Summary
Lichens are symbiotic organisms composed of algae or cyanobacteria and fungi. The composite body of a lichen is called a thallus. Thalli are anchored by rhizines and come in three main types: crustose (crustlike), foliose (leafy), and fruticose (shrubby or hanging). In a heteromerous thallus, the most common type, the fungus forms distinct layers: the upper cortex, medulla, and lower cortex, with the algal cells sandwiched between the cortex and medulla. The upper cortex provides protection and may contain pigments.12
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