Polystichum acrostichoides (Christmas Fern)

Plant Info
Also known as:
Genus:Polystichum
Family:Dryopteridaceae (Wood Fern)
Life cycle:perennial
Origin:native
Status:
  • State Endangered
Habitat:part shade, shade; average moisture to dry; rich hardwood forest, shaded river bluffs, ravines, rocky slopes
Fruiting season:June - October
Plant height:1 to 3 feet
Wetland Indicator Status:GP: FACU MW: UPL NCNE: FACU
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Fiddlehead:

[photo of fiddleheads] Fiddleheads emerge starting in early spring, light green and densely covered in silvery scales.

Leaves and stems: Leaf attachment: basal Leaf type: compound

[scan of fertile frond] Leaves (fronds) are evergreen, once compound, lance-linear in outline, widest near the middle, somewhat narrowed at the base, 12 to 36 inches long, about 4 inches wide, with 20 to 30 pairs of leaflets (pinnae) mostly alternately attached. Fertile fronds are longer than sterile fronds, the fertile fronds having a longer taper at the tip end, the pinnae on the upper portion of the frond abruptly and progressively smaller. Pinnae are generally oblong in outline with a distinct lobe (auricle) at the base on the upper edge; tips are blunt to pointed, sometimes abruptly narrowed.

[photo of pinnae lobes, venation and scaly stem] Veins are forked or with forked branches. Edges are mostly shallowly toothed, usually with a slender spine at the tip of a tooth, but may be toothless. The upper surface is medium to dark green and hairless, the lower surface paler and hairless though hair-like scales may be along the midvein. Pinnae stalks are less than 1mm long.

[photo of scaly stipe bases] The central stem (stipe) is grooved, green for its entire length, and is covered in brown scales all along its length, more densely at the base and the scales becoming hair-like on the upper stem. The plant grows in an asymmetrical clump, the fertile fronds mostly erect to ascending and the shorter sterile fronds mostly arching. Small colonies may form from scaly rhizomes.

Spores: Fruit type: spores on leaf

[photo of mature sori, with hair-like scales on the pinnae] The sori (group of spores) are found on the underside of the pinnae, only on the upper half to 1/3 of fertile fronds, maturing to brown starting in early summer. Sori form along each side of the pinnae midvein and expand to eventually cover the entire surface. A stalked, round tissue (indusium) partly covers the spores and turns dark brown to blackish.

Notes:

Christmas Fern is very rare in Minnesota, reaching the northwest tip of its range in the state. According to the DNR, it was first discovered in 1979 at two locations, one each in Houston and Winona counties. Listed as a Special Concern species in 1984, it was elevated to Threatened in 1996 then Endangered in 2013 after biological surveys failed to discover any additional sites. It is currently a Special Concern species in Wisconsin. Its greatest threats are degradation or destruction of its forest habitat from logging and other exploitive activities, as well as invasive species such as buckthorn, garlic mustard, and earthworms. It is not likely to be confused with other ferns. While the pinnae shape and overall form is similar to Ebony Spleenwort (Asplenium platyneuron), Christmas Fern is more robust and set apart by the scaly stems and sori covering nearly the entire surface of fertile pinnae. It is said that photosynthesis continues into winter, the fronds lying flat to minimize drying out by cold, winter winds. Christmas Fern is rare in the wild but is readily available in the nursery trade.

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More photos

Photos by K. Chayka taken at Eloise Butler Wildflower Garden. Photos by Peter M. Dziuk taken in gardens in Anoka and Hennepin counties. Photos by John Thayer taken in Maine. Polystichum acrostichoides fiddleheads by and (c)2007 Derek Ramsey (Ram-Man) (Self-photographed) [CC BY-SA 2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/2.5-2.0-1.0)], via Wikimedia Commons

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