Polystichum acrostichoides

Polystichum acrostichoides (Michx.) Schott
(from Acrostichum, leather ferns, another genus of ferns with many crowded sori—Nelson 2000, and -oides, like or resembling)

Local names: Christmas fern, dagger fern

Rhizomes erect; leaves evergreen, clustered, to 70 cm long, the blades elliptic-lanceolate to lanceolate in outline, 1-pinnate; pinnae numerous, mostly alternate, auricled basally, the auricle on the acroscopic side (= side toward the leaf apex) of the pinna, the margins bristle-toothed; petioles densely scaly; leaf blades partially dimorphic, the proximal pinnae (those near blade base) sterile, the distal pinnae (those near blade tip) of some blades fertile and conspicuously contracted (but blade tissue still evident); sori round, crowded in usually 2 rows, medial, often confluent at maturity and covering much of lower surface of fertile pinnae; indusia peltate, entire, persistent; 2n = 82 (Wagner 1993). Rich wooded slopes, moist areas; Pineywoods and Post Oak Savannah w to Anderson (Turner et al. 2003), Waller, Wood (Correll 1956; TAES), and Red River (Correll & Correll 12380, BRIT, TEX-LL) cos.; also n Gulf Prairies and Marshes; se Canada and throughout e U.S. w to MN and TX; also disjunct to ne Mexico (Nuevo Leon and Tamaulipas, Mickel & Smith 2004) and naturalized in Europe. Sporulating May–Nov. [Nephrodium acrostichoides Michx.] According to Correll (1956), “In some areas the evergreen fronds are gathered for decorative greens at Christmas time, hence the common name.” Dunbar (1989) also noted that the prominent “ear” (auricle) at the base of each of the pinnae causes the pinnae, when held vertically, to resemble Christmas stockings. Experimental evidence (Noodén & Wagner 1997) suggests that it is beneficial for the leaves to remain green in winter. Two hypotheses for this benefit are: 1) extension of the period of photosynthesis into the winter, and 2) nutrient storage in the old leaves requiring only a single transfer of nutrients to new leaves in the spring (versus two transfers if storage is in the rhizomes). Additionally, Greer and McCarthy (2000) found that as the sporophyte developed, the “rhizome is superseded by the fronds as the primary storage organs.” Wagner et al. (1970) pointed out that plants with deeply incised (vs. toothed) fronds are the result of deviant late season growth developing from cold-damaged leaf primordia.

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