Roccella phycopsis
Litmus
So you've probably heard of a litmus test. Ever wondered what that is? Well a litmus test is a chemical test used to figure out if substance is acidic or basic, and litmus (from Old Norse meaning "moss used for dying,") is derived from lichens!!! It is unclear exactly which Roccella lichens were originally used to make litmus (people weren't so careful about species ID back in the day, ya know?), but R. phycopsis is among the original litmus lichens. This fruticose lichen has terete, erect branches which grow in small tufts out of a basal holdfast attached to costal rock, cliffs, walls, and shrubs. It is pale gray-brown, and has bulging or spikey soralia producing white soredia. The basal holdfast has a characteristic orange or ochre medulla (internal layer of fungal hyphae). R. phycopsis is rather rare, likely due in part to overharvesting for its use as a source for purple dye stretching back to the Roman empire! And inevitably due to the destruction of suitable costal habitat. So yeah, I hope y'all learned something new today, and the next time someone mentions a "litmus test," interrupt whatever they are saying in order to share this fun fact, and encourage them to conserve costal habitats for the preservation of these special little guys.
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