Polystichum lemmonii L. Underwood

Shasta fern

Etymology After John Gill Lemmon, 1832-1908, a collector in the American west.
Description Rhizome: erect.
Frond: 35 cm high by 6 cm wide, evergreen, monomorphic , blade/stipe ratio: 3:1 to 4:1.
Stipe: grooved, sparsely scaly, reddish brown, abruptly diminishing in size distally, vascular bundles: 4 or more, in an arc.
Blade: 2-pinnate, scarcely narrowed at base, linear to lanceolate, very erect, glossy, stipe scales pale tan, microscales narrowly lanceolate, confined to costa of both surfaces.
Pinnae: ovate, folded inward and twisted horizontally, 0.5--2 cm; base truncate to oblique; margins entire to weakly dentate; veins free, forked.
Sori: round, seemingly scattered at random on fertile pinnae, indusium: peltate, central, sporangia: dark brown to blackish.
Dimensionality: pinnae twisted horizontally.
Culture Habitat: rocky serpentine slopes, uncommon. Distribution: British Columbia to central California. Hardy to -20C, USDA Zone 6. Unlikely to be in cultivation..
Distinctive Characteristics Non-spiny, the only such Polystichum here.
Synonyms
Polystichum mohrioides (Bory) C. Presl var. lemmonii (L. Underwood) Fernald
Aetopteron lemmoni House
Polystichum lemmonii
Polystichum lemmonii. a) frond, b) fertile pinna.  Illustration by V. Fulford from Ferns and Fern Allies of Canada, William J. Cody and Donald M. Britton, 1989, Agriculture Canada, used with permission.
Notes
Serpentine Arthur Kruckeberg: "Of the western ferns on serpentine, only Polystichum lemmonii is obligate," personal communication.
Stipe Scales The description of the stipe as "sparsely scaly" in FNA (along with an illustration there) contradicts the drawing here. A drawing in How to Know the Ferns and Fern Allies, J.T. Mickel, shows no scales at all. At CalPhotos (see the link), sparsely seems appropriate.
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