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FNA | Family List | FNA Vol. 2 | Dryopteridaceae

12. Polystichum Roth, Tent. Fl. Germ. 3: 31, 69. 1799.

[Sword fern, Christmas fern, holly fern[Greek poly, many, and stichos, row, presumably in reference to the rows of sori on each pinna]

David H. Wagner

Plants terrestrial. Stems decumbent to erect, stolons absent. Leaves monomorphic (dimorphic in P . acrostichoides ), evergreen. Petiole 1/9--1 times length of blade, bases swollen or not; vascular bundles more than 3, arranged in an arc, ± round in cross section. Blade linear-lanceolate to broadly lanceolate, 1--3-pinnate, gradually reduced distally to pinnatifid apex, somewhat leathery to leathery. Pinnae not articulate to rachis, segment or pinna margins spinulose-toothed (except P . lemmonii ); proximal pinnae (several pairs) usually gradually reduced, sessile to short-petiolulate, bases usually inequilateral with acroscopic lobe; costae adaxially grooved, grooves continuous from rachis to costae; indument of linear to lanceolate scales on costae and sometimes between veins abaxially (microscales), ± glabrous or similarly scaly adaxially (scales forming loosely tangled network over blade and sori in P . dudleyi ). Veins free, forked, rarely ( P . imbricans ) anastomosing. Sori in 1 row (to several) between midrib and margins, round (confluent, covering abaxial surface in P . acrostichoides ); indusia peltate, persistent or caducous [absent]. Spores yellow or brownish to black, with inflated folds. x = 41.

Species ca. 180 (15 in the flora): worldwide.

The mating systems of Polystichum seem to be highly outcrossing (P. S. Soltis and D. E. Soltis 1987; P. S. Soltis et al. 1989); hybrids are frequent where two or more species occur. Sterile hybrids are discussed under one of their putative parents.

Sterile hybrids are best recognized by their misshapen sporangia, which produce little black dots at the end of the season instead of forming the fuzzy brown bump typical of sori after spores have been expelled. In many cases the intermediacy and robustness of hybrids make them stand out as odd. At least one or two hybrid plants are to be expected in large, mixed populations. The allopolyploids, having hybrid origins, present particular problems. They exhibit the Vavilov effect: allopolyploids tend to resemble one of their parental species when they grow with, or in the habitat typical of, that species (D. S. Barrington et al. 1989).

In the flora there are six diploids, five tetraploids, one hexaploid, and three species whose chomosome number is unknown. Relationships among the diploids are generally not very close; that is, each is probably more closely related to a species outside the flora than to one of the other species in the flora. The exception to this is the group composed of Polystichum acrostichoides , P . imbricans , and P . munitum . Polystichum acrostichoides appears to share a Tertiary common ancestor with P . munitum , and P . imbricans is more recently derived from P . munitum . All of the polyploid species are fertile allopolyploids. One of these species ( P . braunii ) is also involved in the formation of the hexaploid P . setigerum (see below).

Relationships among Polystichum Species

Allopolyploid Presumed Originating Crosses andersonii kwakiutlii × munitum californicum dudleyi × imbricans or dudleyi × munitum kruckebergii lemmonii × lonchitis scopulinum lemmonii × imbricans or lemmonii × munitum setigerum braunii × munitum

The morphological similarity among Polystichum species may make identification difficult, particularly among the species with more divided leaves. The keys presented here are designed for mature, typical individuals. Some of the characters mentioned in the keys and descriptions require the use of a microscope. The microscales (small trichomes that occur on the abaxial leaf surface of all species and adaxially in some) are best observed by peeling them off with cellophane tape and mounting the tape on a slide, sticky side up, under a coverslip. The tape can also be used to lift off the components of the sori. Polystichum acrostichoides , P . andersonii , P . lemmonii , and P . munitum are known to have sclereid clusters in their pith. Polystichum imbricans lacks such clusters, and data are not available for the other species.


Wagner, D. H. 1979. Systematics of Polystichum in western North America north of Mexico. Pteridologia 1: 1--64. Wagner, W. H. Jr. 1973. Reticulation of holly ferns (Polystichum) in the western United States and adjacent Canada. Amer. Fern J. 63: 99--115. Welsh, S. L. 1974. Anderson's Flora of Alaska and Adjacent Parts of Canada. Provo. Yatskievych, G., D. B. Stein, and G. J. Gastony. 1988. Chloroplast DNA evolution and systematics of Phanerophlebia (Dryopteridaceae) and related fern genera. Proc. Natl. Acad. Sci. U.S.A. 85: 2589--2593.

1 Fertile pinnae contracted, sori confluent, completely covering abaxial surface.   1 Polystichum acrostichoides
+ Fertile pinnae not contracted, sori often distinct.   (2)
2 (1) Leaves 1-pinnate.   (3)
+ Leaves 1-pinnate-pinnatifid or 2-pinnate.   (6)
3 (2) Pinnae denticulate but not spiny; pinna apex rounded; microscales dense on both leaf surfaces; restricted to the Aleutian Islands.   2 Polystichum aleuticum
+ Pinnae serrulate-spiny; pinna apex acute to cuspidate; microscales prominent on abaxial surface only; widespread.   (4)
4 (3) Petioles mostly less than 1/6 length of leaf; blades narrowing toward base; proximal pinnae ±deltate; pinnae spreading-spinulose.   11 Polystichum lonchitis
+ Petioles usually greater than 1/5 length of leaf; blades narrowing slightly, if at all, toward base; proximal pinnae auriculate-ovate to falcate; pinnae incurved-spinulose.   (5)
5 (4) Indusia ciliate; pinna apex acuminate, base cuneate.   13 Polystichum munitum
+ Indusia entire to sharply dentate; pinna apex apiculate or cuspidate, base oblique.   7 Polystichum imbricans
6 (2) Leaves 2-pinnate, pinnules petiolate.   (7)
+ Leaves 1-pinnate-pinnatifid but in some species with deeply incised pinna margins appearing 2-pinnate, segments (pinnules) sessile, adnate to costa for at least 2 mm.   (10)
7 (6) Pinnules rounded at tip, margins not spiny.   10 Polystichum lemmonii
+ Pinnules apiculate at tip, margins spiny.   (8)
8 (7) Proliferous bulblets present on distal portion of leaves.   9 Polystichum kwakiutlii
+ Proliferous bulblets absent.   (9)
9 (8) Blades narrowed toward base; microscales on abaxial surface dense but not forming tangled network.   4 Polystichum braunii
+ Blades not narrowed toward base; microscales on abaxial surface forming loosely tangled network over blades and sori.   6 Polystichum dudleyi
10 (6) Microscales lanceolate to linear-lanceolate, on abaxial leaf surface only; leaves often smaller than 3 dm; to 3500 m.   (11)
+ Microscales filiform on both leaf surfaces; leaves often larger than 3 dm; to 1700 m.   (12)
11 (10) Pinna apex with spreading teeth (visible without magnification), subapical teeth nearly equal to apical tooth; apex of at least proximal pinnae acute.   8 Polystichum kruckebergii
+ Pinna apex with incurved teeth, subapical teeth much smaller than apical tooth; pinnae apices obtuse.   14 Polystichum scopulinum
12 (10) Rachis with 1 or more bulblets at pinna base(s) on distal 1/3 of blade.   3 Polystichum andersonii
+ Rachis without bulblets.   (13)
13 (12) Pinnae not incised to costa; California to s British Columbia.   5 Polystichum californicum
+ Pinnae incised to costa; s British Columbia northward.   (14)
14 (13) Pinnule margins spinulose-dentate but not incised; Alaska to British Columbia.   15 Polystichum setigerum
+ Pinnule margins deeply incised; w tip of Aleutian Islands.   12 Polystichum microchlamys

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