dwell on bamboo, with the exception of A. philodendri, described from specimens resembling A. polychrous but found growing on a Philodendron sp.. The striations in the stick seen here say bamboo to me, eliminating the oddball of the genus from the list of possibilities.
Under the remarks for A. philodendron’s maiden description it’s mentioned that it resembled A. polychrous in almost every way, save for some minor size discrepancies and the difference in substrate. One of those shared characteristics is purple coloration, which leads me to think that this observation may be of Möller’s A. polychrous.
I’m copying his original description as we speak for the ‘Notes’ section of its name page. We’ll see how it stacks up against these images once it’s finished.
As for the ‘polyporus’ part of the name, it has to do with the tiny pores produced on the underside of the fruiting bodies. While they superficially resemble the pores of a conk, they’re actually downward-facing ostioles inside of which the perithecia are formed.
This specimen is immature, so the pores aren’t fully developed. Larger fruiting bodies actually become shelf-/bracket-like with visible “pores” underneath (see Fig. 1 B in the Mycologia article)