Texas Star -- Fungus only found in Texas and Japan

Title says it all. Chorioactis geaster is only found in the planes of central-northern Texas, and the mountains of southern Japan. Question is, how did this range come to be?

https://en.wikipedia.org/wiki/Chorioactis

https://www.jstor.org/stable/41761789?seq=1

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Weird. These fungi seem to be textbook examples of paleoendemism, where a widespread species becomes restricted to a small part of its former range. This one just got restricted to two parts of its former range. There are other groups with similarly counterintuitive distributions where modern populations arise from a more widespread group, like the genus Torreya.

What’s most interesting to me is to see a species with such deep temporal divergence and such little noted morphological differences. 19-81 million years since divergence is a long time. Even on the low end, and even in conservative groups I would expect nearly 20 million years of independent evolution to produce some level of divergent characters. And on the upper end that is unfathomably deep time. I understand why some mycologists want to split largely based on DNA after looking at this.

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Another textbook example but of a higher taxon are Sequoioideae that now are only found in China and USA.

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