Stems ascending. Leaves erect, 1--2.5 dm; bulblets absent. Petiole 1/10--1/5 length of leaf, sparsely scaly; scales light brown, gradually diminishing in size distally. Blade linear, 1-pinnate-pinnatifid, base narrowed. Pinnae rhombic-ovate to short-falcate, proximal pinnae ± triangular; pinnae overlapping, twisted somewhat out of plane of blade, 0.5--1.5 cm; base oblique, acroscopic auricle well developed; margins shallowly incised to merely dentate or serrulate, teeth spreading and spiny at tip; apex acute with subapical and apical teeth same size; microscales lanceolate with few projections, confined to costa, on abaxial surface only. Indusia entire. Spores dark brown. 2 n = 164.

Rocks and cliffs in subalpine to alpine habitats; 1500--3200 m; B.C.; Calif., Idaho, Mont., Nev., Oreg., Utah, Wash.

Polystichum kruckebergii is widely but sporadically distributed in small numbers in both the Sierra-Cascade and Rocky Mountain systems. Populations sometimes consist of only two or three dwarfed plants that are difficult to distinguish from P . scopulinum , with which they may occur. The spreading teeth of equal size at the pinna apex will usually distinguish this species. Polystichum kruckebergii is a tetraploid presumed to be of hybrid origin, with P . lonchitis and P . lemmonii as its diploid progenitors (W. H. Wagner Jr. 1973), although this hypothesis has not been confirmed. The hybrid with P . munitum has been found in Washington (P. S. Soltis et al. 1987) with both parents, and it is distinguished by intermediate morphology and abortive sporangia.