Lichens cannot regulate their own water content and photosynthesize only when wet

Evidence

Lichens are opportunistic, making efficient use of resources when they’re available and otherwise happily doing without. Most of the time when you encounter Umbilicaria it is as crisp and dry as a dead leaf, but it’s far from deceased. It is only waiting, empowered with a remarkable physiology to endure drought. Like the mosses with whom it shares the rocks, lichens are poikilohydric: they can photosynthesize and grow only when they are wet, but they are not able to regulate their own water balance—their moisture content mirrors the moisture in the environment. — Robin Wall Kimmerer, Braiding Sweetgrass, 999

Categorization

• DEFINE: Introduces poikilohydric as a technical term for organisms whose moisture mirrors the environment.