41. Dryopteris erythrosora (Eaton) Kuntze (Rev. Gen. Pl. 2: 812. 1891).—Autumn fern.—Fig. 43.

Rhizome erect-ascending to prostrate, stout, branching to form a few adjacent crowns. Stipes 30—60 cm long, irregularly clustered, the larger scales mostly very narrow, stiffish, somewhat glossy, blackish brown to black, ca. 10 mm long; blade 30—70 cm long, 15—35 cm wide, typically broadly ovate to oblong, to 2-pinnate; pinnae 8—20 pairs, pinnatisect to pinnate, their apices pinnatifid, acuminate, the bullate scales of the costa fairly persistent, often dense and dark; pinnules narrow-oblong to linear-lanceolate, acute to rounded, the margins subentire, serrate, crenate-serrate or incised-serrate, the teeth mucronate or spinescent and sometimes incurved, the basiscopic pinnule next to the rachis on the lowest pinnae usually reduced. Sori often closer to the midrib than medial; indusia round reniform, quite evenly placed, at maturity red; for greenish white indusia see f. viridosora.
                                                                                                                                                     
Dryopteris erythrosora is an apogamous triploid species from eastern Asia, where is grows in woods in low mountains and hills. It is a very common and very variable species. Because of its variability this species is often confused with others. The 2-pinnate, broad frond, the short basiscopic pinnule next to the rachis on the proximal pinnae, the many non-opposite pinnae, and the frequently incurved spinulose tipped teeth, often dark-tipped bullate scales, help somewhat to distinguish it from most U.S. cultivated Dryopteris. In the southern California trade, it is much confused with the similar appearing D. hondoensis (which see). Plants currently circulating in the Pacific Northwest as D. bissetiana and D. purpurella are D. erythrosora variants, these variants often have more triangular fronds and deeply serrate lobed pinnules than typical D. erythrosora. True D. bissetiana and true D. purpurella (which see) are very rare in U.S. and appears distinctly different.

The range of variability of Dryopteris erythrosora in U.S. gardens includes differences in height of the plant, the arching or spreading habit of the fronds, the fullness and shape of the blade and its divisions, particularly the degree of lobing in the pinnules, the intensity of the green blade color, the length of the stipe, thinness or brittleness of the blade tissue, color of the indusia, and also other features.

Dryopteris erythrosora has medium to large fronds, is hardy to a January average somewhat above 30°F. It is a robust grower and easily cultured.The new growth is often a pinkish or reddish bronze, which is more pronounced on some plants than on others. This species is valued for its shiny evergreen foliage. Plants with red or maroon-red indusia provide an added interest.

The following are found in cultivation. These were originally published as formae, but some authors believe that they are best regarded as cultivars:

D. erythrosora f. prolifica (Maxim. ex Franch. & Sav.) H. Itô in Takai & Honda (Nov. Fl. Jap. 4:41. 1939).—Blade deltoid, often with buds; pinnules strongly contracted, linear shaped, apex sharply pointed. The original plant was found among wild plants in Japan. Small-medium plant of easy culture.

D. erythrosora f. viridosora (Nakai ex H. Itô) H. Itô (Bot. Mag. (Tokyo) 50: 68-69. 1936. [also see H. Itô in Nakai and Honda, Nov. Fl. Jap. 4: 41. 1939]).—Indusia when mature whitish-green. Native to Japan. The form with white indusia belongs to f. viridosora. Judith Jones of Fancy Fronds Nursery, Seattle, Washinton (pers. comm.), reports that spores from D. erythrosora with the normal greenish-white indusia produce plants with red indusia and less frequently with very white indusia. Martin Rickard of England (pers. comm.) also reports that sowings of spores from plants with greenish-white indusia yield some plants with red indusia.