Ectophloic

Ectophloic refers to a type of lichen growth form where the algal or cyanobacterial cells are located in the outer layer of the thallus, beneath the cortex. This is in contrast to endophloic lichens, where the photobiont is embedded within the fungal hyphae. Ectophloic lichens are characterized by having a distinct upper cortex made of fungal tissue, followed by a layer containing the photosynthetic partner, and then typically a medulla and a lower cortex. This arrangement is common in many foliose (leaf-like) and some fruticose (shrub-like) lichens. The positioning of the algal cells in the ectophloic structure is crucial for efficient light absorption while providing protection from desiccation and UV radiation by the overlying fungal cortex. The thickness and composition of the cortex can vary significantly between species, influencing the overall appearance and ecological niche of the lichen. Identifying whether a lichen is ectophloic or endophloic often requires microscopic examination of its internal structure.