Polystichum imbricans
Polystichum acrostichoides
imbricate sword-fern, narrow-leaf sword fern, rock sword-fern
Christmas fern, polystic faux-acrostic
ascending to erect.
erect.
erect to arching back at tip, 2–8 dm;
bulblets absent.
dimorphic (only in this species);
fertile pinnae distal, much contracted;
sterile leaves arching, 3–8 dm;
bulblets absent.
1/4–1/3 length of leaf;
scales abruptly diminishing in size distally and falling off early but retaining conspicuous tuft of brown scales at base.
1/4–1/3 length of leaf, densely scaly;
scales light brown, diminishing in size distally.
linear-lanceolate to linear, 1-pinnate, base not or slightly narrowed.
linear-lanceolate, 1-pinnate;
base narrowed.
oblong, slenderly lanceolate, or falcate, usually overlapping, in 1 plane or twisted out of plane of blade, 2–4 cm;
base oblique, auricles well developed;
margins serrulate-spiny with teeth ascending;
apex cuspidate or apiculate with subapical teeth smaller than apical tooth;
microscales lanceolate to linear with straight or sharply angular projections, sparse, on abaxial surface only.
oblong to falcate, not overlapping, in 1 plane, 2–6 cm;
base oblique, acroscopic auricles well developed;
margins serrulate-spiny with teeth ascending;
apex acute or blunt with subapical and apical teeth same size;
microscales filiform, lacking projections, dense, on abaxial surface only.
entire to sharply dentate.
confluent, completely covering abaxial surface of pinnae (only in this species);
indusia entire.
dark brown.
light brown.
= 82.
Polystichum imbricans
Polystichum acrostichoides
Polystichum imbricans is one of the postulated ancestors of two allopolyploids, P. californicum and P. scopulinum (D. H. Wagner 1979). Relationships to P. munitum are discussed under that species.
Subspecies 2.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Polystichum acrostichoides is a common species most closely related to P. munitum (G. Yatskievych et al. 1988), which also occurs extensively on forest floors.
The dimorphic pinnae of Polystichum acrostichoides are not unique to the genus; they are found also in some Asian species. Numerous variants have been named, mostly as forms, but none are of taxonomic consequence. Hybrids are known with P. braunii (P. × potteri Barrington) and P. lonchitis (P. × hagenahii Cody). The latter hybrid is rare, known only from its type locality in Ontario, where it grows with both parents. It is recognized by its intermediate morphology (leaves wider than P. lonchitis, narrower than P. acrostichoides, with slightly contracted sorus-bearing pinnae) and malformed sporangia and spores. Polystichum × potteri is much more widespread, from Nova Scotia, New Brunswick, and Quebec through New England to Pennsylvania. It resembles P. braunii but has narrower leaves bearing malformed sporangia.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Pinnae oblong, less than 5 times longer than wide, adaxial surfaces facing upward and twisted out of plane of blade; leaves stiffly erect to tip; at base of boulders or in cliff crevices in exposed sites; California to British Columbia. | subsp. imbricans |
1. Pinnae narrowly lanceolate, more than 5 times longer than wide, generally in 1 plane; leaf tips arching back; on forest floor in shade; only in California. | subsp. curtum |
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