Ephemeron

I learned the word "ephemeron" today (plural "ephemera"), which I had assumed was a noun applied to something ephemeral, and though that is the case, it can specifically pertain to printed matter "of passing interest" like brochures and pamphlets. At our library, however, where I learned this word, ephemera are not so ephemeral as we've got them catalogued in our permanent collections. Which is sort of strange. Also important to note, ephemera are a kind of short-lived mayfly. Oh, the things that occupy my mind.