Gymnocarpium dryopteris has small, delicate fronds up to 40 cm (16 inches) long, with ternately-compound pinnae (leaves). Fronds occur singly. Each petiole grows from one node on a creeping rhizome.[7] Fronds occur singly. On the underside of matured pinnae the naked sori can be found (the Latin generic namegymnocarpium means "with naked fruit").[8] The species grows in coniferous woodlands and on shale talus slopes.[2]
Despite its common name, Gymnocarpium dryopteris, a forest understory plant, is not found in association with Quercus (oak).[9][10]
Like most plant species, oak fern alternates generations, where there is a diploid generation in the form of a sporophyte (which produces spores), and is followed by a haploid generation in the form of a gametophyte (which produces gametes).[14] The sporangia are found in clusters on the underside of the leaf, called sori.[15] Each sporangium produces multiple sporocytes, with each sporocyte dividing twice, giving rise to four non-sexual spores.[15] Once the spores germinate, they form a prothallus, which develops a number of archegonia (ovaries), and antheridia (spermaries).[15] If water is present, the spermatozoids travel from the antheridia to the archegonia and the egg is fertilized when the two come into contact. An embryo then grows out of the gametophyte, producing a sporophyte.[15]
Habitat
Oak fern commonly occurs in moist, shady forests, with wet soil and humid conditions.[16] Often found in drainage areas, ditches and north-facing slopes,[17] it thrives in soils that are well-drained and have a ph of 4.5-6.4.[16][17] Soil texture varies from silty, clay-loams, to sandy gravel.[18] This fern occurs at elevations of 1,700–4,500 ft (520–1,370 m) along moderately steep slopes with north, east and west aspects.[18] As it is extremely sensitive to ecological changes, the northern oak fern is an important moisture indicator species.[19]
Gallery
The leaf of the fern Gymnocarpium dryopteris, showing sori (groups of sporangia).
^ abCooper, Stephen V.; Neiman, Kenneth E.; Roberts, David W. (1991). Forest habitat types of northern Idaho: A second approximation (Report). Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. doi:10.2737/int-gtr-236.
^Winkel, A., & Wood, L. J. (2022). Population-level drought responses in northern oak fern (Gymnocarpium dryopteris). Botany, 100(9), 753–760. https://doi.org/10.1139/cjb2021-0114