1 Leaves bipinnate-pinnatifid to tripinnate-pinnatifid (or to quadripinnate in the lower pinnae), divided 2.5-4×; [“clade II”].

  2 Leaves evergreen, the blades appearing more-or-less parallel-sided and minutely glandular-pubescent, especially on the indusium, rachis, and pinnae midribs; first basal-pointed pinnule of the basal pinna shorter than or equal to the next outermost basal-pointed pinnule; first basal-pointed pinnule of the basal pinna usually < 2× as long as the first tip-pointed pinnule of the basal pinna

  2 Leaves deciduous, the blades appearing more or less triangular and lacking gland-tipped hairs (except occasionally on the indusium); first basal-pointed pinnule of the basal pinna longer than the next outermost basal-pointed pinnule; first basal-pointed pinnule of the basal pinna > 2× as long as the first tip-pointed pinnule of the basal pinna.

    3 Leaf blade ca. 1× as long as the petiole; indusium occasionally glandular; first basal-pointed pinnule of the basal pinna 2.5-5× as long as the first tip-pointed pinnule of the basal pinna

    3 Leaf blade 2× as long as the petiole; indusium glabrous; first basal-pointed pinnule of the basal pinna ca. 2× as long as the first tip-pointed pinnule of the basal pinna

1 Leaves pinnate, pinnate-pinnatifid, to bipinnate (or to bipinnate-pinnatifid in the lower pinnae), divided 1-2.5×.

      4 Leaves pinnate, divided 1× (the pinnae toothed, but not further lobed or divided); rachis densely clothed with blackish scales; ["clade I"]

      4 Leaves pinnate-pinnatifid to bipinnate (or to bipinnate-pinnatifid in the lower pinnae), divided 1.5-2.5×; rachis sparsely to moderately clothed with light tan to brown scales.

        5 Sori marginal (no blade tissue visible on the underside of the blade between the sori and the margins); leaves evergreen, gray-green, leathery in texture; [“clade I”]

        5 Sori medial or submedial (some blade tissue visible on the underside of the blade between the sori and the margins); leaves evergreen or deciduous, dark- to bright-green, thin to stiff in texture.

          6 Scales of the petiole, rachis, and costae of 2 distinctly different types (broad vs. hairlike); leaves with 20-30 pairs of leaflets; [PA northwards]; [“clade I”]

          6 Scales of the petiole, rachis, and costae broad, variable in size, but lacking scales of a hairlike type; leaves with 10-25 pairs of leaflets; [collectively widespread].

             7 Leaves dimorphic, the deciduous, fertile leaves erect, 2-3× as long as the spreading, evergreen, sterile leaves, which form a winter "rosette"; fertile leaves linear-lanceolate in outline, generally 4-8× as long as wide; pinnae mostly 1.5-3× as long as wide, triangular; scales at base of petiole tan; [“clade II”].

               8 Fertile pinnae nearly in plane of the blade (like a closed Venetian blind); fertile leaves 12-20 cm wide

               8 Fertile pinnae usually twisted out of the plane of the leaf axis, often nearly to 90° (like an open Venetian blind); fertile leaves 8-12 cm wide

             7 Leaves not dimorphic, or only slightly so, deciduous (D. goldieana), evergreen (D. ludoviciana) , or else with usually deciduous fertile and semi-evergreen sterile fronds (D. celsa); fertile leaves lanceolate to ovate in outline, generally 1.5-4× as long as wide; pinnae mostly 3-5× as long as wide; scales at base of petiole dark brown with tan margins.

                 9 Costa with bullate (blistered-appearing) scales abundant, usually dark; [naturalized exotic]; [“clade V”]

                 9 Costa lacking bullate scales; [native, sometimes also cultivated]; [“clade III”].

                   10 Leaves evergreen, fertile only toward the tip, the fertile pinnae and segments narrower than the sterile and more widely spaced; scales at the petiole base light brown, not shiny.

                     11 Fertile leaflets only slightly narrower than the sterile leaflets and spaced similarly along the rachis; teeth tapering to sharp points; spores shrunken and irregular

                     11 Fertile leaflets much narrower and obviously more widely spaced along the rachis than the sterile leaflets; teeth triangular (acute); spores full

                   10 Leaves deciduous or semi-evergreen, fertile throughout or nearly so, the fertile pinnae and segments not differentiated from sterile ones; scales at petiole base medium to dark brown, shiny or not.

                       12 Sterile leaves semi-evergreen; fertile leaves deciduous with sori submedial, not touching the costule at maturity; leaf blade lanceolate, usually 2-4× as long as wide, gradually tapering at the apex; scales at the petiole base medium to dark brown, with a narrow black central band