Peltigera hydrothyria
Eastern waterfan, watershield lichen
No, you are not mistaken: this is an aquatic lichen! One of the very very few entirely aquatic lichens. P. hydrothyria can be found in eastern North America, where it lives in sheltered, shady, unpolluted streams by attaching to rock near or below the waterline. It has a foliose thallus made up of fan-shaped, undulating lobes. The upper surface is dark purple-brown or bluish-green in color, and the lower surface is lined with pale, branching veins. When wet, the lobes become translucent, making it difficult to tell the upper surface from the lower surface. It produces orange-brown apothecia at the lobe apex or on the edge of the lower surface. Like many hydrophilic lichens, P. hydrothyria has a cyanobacterial (in this case a Nostoc) photobiont. Due to its limited range and reliance on undisturbed habitats, it is currently classified as "endangered" on the Global Fungal Red List, where all the hot girls are.
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