Dryopteris intermedia

Dryopteris intermedia is a perennial fern that grows to a size of about {{convert|40|–|90|cm|in|abbr=on}} tall and {{convert|60|–|90|cm|in|abbr=on}} wide. At its base, it consists of an underground rhizome from which grow the fronds of the plant in a spiral-like arrangement. Each frond consists of a stipe (stalk) that is covered in light-brown scales towards the base and short glandular hairs further up. The stipes generally measure between 1/4 to 1/3 the length of the frond and support a leaf blade that is lance-oblong in shape. The leaves themselves are bipinnately compound, meaning that they divide into leaflets called pinnae and sub-leaflets called pinnules. The pinnules of this species are lobed and toothed. Uniquely, the first pinnule closest to the stem on the lowest pinna is shorter than the second.

Dryopteris intermedia is native to most of eastern North America, ranging from Minnesota in the north-west and Newfoundland and Labrador in the north-east, down to Alabama in the south-west and South Carolina in the south-east. While globally secure, it is considered by NatureServe to be "critically imperiled" in the states of Iowa and Missouri which represent the western limit of its range, and "imperiled" in the states of Illinois and South Carolina as well as the region of Labrador. Similar ferns found in the Azores are often regarded as a subspecies (subsp. azorica) or as a different species (Dryopteris azorica).{{cite web |title=Dryopteris intermedia subsp. azorica (Christ) Jermy |url=https://www.catalogueoflife.org/data/taxon/5GZJJ |publisher=Catalogue of Life |access-date=24 June 2021}}

Dryopteris intermedia grows in a variety of mesic habitats including forests, woodlands, ravines, swamp edges and rocky slopes.

Dryopteris intermedia is cultivated as an ornamental plant in North America for gardens, especially natural gardens and shade gardens, as it is easy to grow in a range of environments and soils and does not spread much. Care needs to be taken when planting to ensure that the fern is placed in an area of part-shade or full-shade and that the soil remains moist, as it does not tolerate a lot of sun or dry soil.

Several naturally occurring hybrids involving Dryopteris intermedia exist. These include:

• Dryopteris campyloptera × Dryopteris intermedia ("hybrid wood fern")
• Dryopteris intermedia × Dryopteris marginalis ("glandular marginal wood fern")
• Dryopteris ×boottii ("Boott's wood fern")
• Dryopteris ×triploidea ("triploid wood fern")
• Dryopteris ×dowellii ("Dowell's wood fern")
• Dryopteris goldieana × Dryopteris intermedia ("hybrid wood fern")

All of the hybrids listed above are sterile. One exception is the allotetraploid Dryopteris carthusiana (spinulose wood fern), which is said to originate from a hybridization of Dryopteris intermedia and an extinct fern dubbed Dryopteris "semicristata".{{cite journal | first1=Emily B | last1=Sessa | first2=Elizabeth A | last2=Zimmer | first3=Thomas J | last3=Givnish | title=Unraveling reticulate evolution in North American Dryopteris (Dryopteridaceae) | url= | date=30 June 2012 | journal=BMC Evolutionary Biology | volume=12 | issue=1 | page=104 | doi=10.1186/1471-2148-12-104 | pmid=22748145 | pmc=3509404 | s2cid=15339339 | doi-access=free | bibcode=2012BMCEE..12..104S }}

Image:Dryopteris intermedia 1zz.jpg|Dryopteris intermedia in Washington, D.C.

Image:Dryopteris_intermedia_pinnules.JPG|Characteristic toothed pinnules

Image:Evergreen-Wood-Fern-sori-b (6264228657).gif|Sori on the underside of the fronds

{{Commons category|Dryopteris intermedia}}

{{Reflist}}

• [http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=200004448 Dryopteris intermedia] - in Flora of North America

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intermedia

Category:Ferns of the Americas

Category:Ferns of Europe

Category:Plants described in 1810

Category:Invasive plant species in Japan