Cladonia prostrata
Resurrection lichen, dune cup lichen
Lichens are poikilohydric organisms, meaning that they cannot control how much water they take in or lose. When their environment is wet, they are wet. When their environment is dry, they are dry. Obviously water is necessary for photosynthesis, so lichens have a diversity of strategies to deal with this inherent stress, well adapted as they are to their climactic niches. One such strategy is visible here in C. prostrata: when moist, the long, deeply incised lobes unfurl, exposing the green algal photobiont in the upper surface to sunlight for photosynthesis, but when dry, the lobes curl and expose the pale underside, stopping photosynthesis while protecting the photobiont cells from photodamage. It basically allows the whole system to shut down until water is available again. This adaptation makes sense in context this lichen's particular survival strategy. The xeric sand pine scrub forests C. prostrata inhabits in Florida and Georgia are prone to fire, leaving the ground exposed to full sun and prone to drying out. By having a built in resistance to photodamage triggered by water loss, C. prostrata is able to survive in this stressful environment, and is in fact one of the first colonizers following a fire event! It helps to stabilize the soil and recharge it with nutrients, helping the system recover as a whole. Pretty cool, huh?
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