Polypodium interjectum is a species of fern.

A medium-sized, ladder-like fern possessing an oval outline (mostly 2-4 x as long as wide), widening from both ends toward the middle or a little below it, with a truncated base abruptly transitioning to its stem, the base leaflets at maturity tending to be folded inwards.

The fertile sori under the leaf are elliptic when very young, and tend to be bright yellow when maturer but unopened.

Technically, sporangia can be scraped off from under the leaf, and under a 200x lens (or better) they on average have a small backbone (annulus) of 7-9 (4-13) thick-walled cells, with 2-3 basal cells that are much wider than the annulus, and no branched long hairs (paraphyses, 0.5-1.4 mm) intermingled.

[2] [3] [4] Similar species include - [2] [3] [4] Most of Europe, far-Western Russia, Turkey and Iran.