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Narrowing a fern down to its family is (usually) easier. After that it gets messy. Let me give you an example. In the Dryopteris family of true wood ferns, three choices are the most likely in the woods around me—Intermediate, Spreading and Fragrant. In order to decide which of those might be the fern you see in today’s photo, the three species are separated by looking at the "first downward pointing secondary leaflet (basiscopic pinnule) on the lowest primary leaflet (basal pinna)." Then after you’ve found that first downward pointing etc., you have to look at the size and width of it as well as how it’s attached to the first upward pointing subleaflet. Okay, maybe I’ll try that tomorrow.
Then there’s the problem of the fieldguides. They ain’t cheap. They ain’t new, either, for the most part. At least, not for the ferns around Pennsylvania. I found one that sounded ideal, but it was $85. I found another that sounded good, it was $35. Another was printed in 1915 and yet another in 1937. This wasn’t exactly what I had in mind.
The internet offered some help, though not on a par with bird or flower identifications. Here’s a link to a page that contains several good links to more pages with some fern identification information.