I'm not too hung up over this detail; in fact the reason why I created this thread was to avoid being hung up over it.
I think it is important. Not on its own, but together with other small things like... - a kind of plant that doesn't exist in the real world - a kind of metal that has special properties but not too special - a kind of critter that is casually mentioned even though they're strange. Surely, this is just a random list of things I made up. My point is: Even if they're not plot-relevant, the little details make the world more interesting and can reinforce the immersion. In my example, it reminds the reader very subtly that 'this is a different world'. However, they must be thought out a bit. If they're not plot relevant you can't make them stand out too much, but they have to make sense. If they are somehow plot-relevant (which seems to be the case here) it is even more important that it doesn't distract from the story.