What is Street Creatures?  This is the game I run on Twitter every Friday. I’ve
collected all the past quizzes here in one place so you can either relive them, or play
them for the first time.

How does it work?  Provided are four, seemingly unrelated clues, that are all
connected by a wild organism that can be found in a city. Look at the four clues,
do some research, and when you think you’ve figured it out, click on ‘Answer’
to reveal what connects the clues, and how they are connected.

Follow me on Twitter to play #StreetCreatures live every Friday at 9am PST.

Quiz #75 Clues

Physodic acid

Answer (Don't click until you've solved it)

Hypogymnia physodes


There are many lichen species used as bioindicators, meaning scientists use their presence, or lack of, or grown forms as an indication of air quality. Hypogymnia physodes is a key species in this science.


One of the identifiers of Hypogymnia species is that their structure is hollow and tube-like giving them the common name ‘tube lichens’.


This is a chemical compound found in Hypogymnia physodes, one of around 1,000 different compounds that have been identified in lichens so far. Lichens are complex, to say the least.

Physodic acid:

Physodic acid is one of the depsidones produced by the lichen. It’s being studied in the field of medicine because lichens have long been used in folk medicine.
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