About Argyrochosma dealbata (Pursh) Windham
Argyrochosma dealbata (Pursh) Windham has a compact, roughly upright, typically unbranching rhizome that bears uniformly colored brown, pale brown, or yellowish-brown scales. These scales are approximately 3 millimeters (0.1 in) long, thin and delicate, shaped like narrow lanceheads or linear, and have entire, toothless edges. The fronds of A. dealbata grow in clusters from the rhizome, reaching 3 to 15 centimeters (1 to 6 in) in length. The stipe, the leaf stalk below the blade, is shiny, ranging in color from pale to medium brown, chestnut brown, or reddish-brown. It measures 2 to 7 centimeters (0.8 to 3 in) long and 0.50 to 0.75 millimeters (0.020 to 0.030 in) in diameter. It is rounded, rather than flattened or grooved, and does not have extensive hairs or scales; a small number of rhizome scales may be present at its base. The stipe’s shiny brown color extends into the rachis (the leaf axis) and the axes of the leaf segments, blending into leaf tissue at the base of each segment without an abrupt stopping point. The rachis is rounded or slightly flattened on its upper surface. The costae, the pinna axes, are roughly straight. All leaf axes tend to curl upward when the plant dries. The leaf blades are deltate (triangular) or lanceolate, widest at their base where they are most highly divided, ranging from tripinnate (cut into pinnae, pinnules, and pinnulets) to pentapinnate (five times divided). Blades are 2 to 6 centimeters (0.8 to 2 in) long and 1.5 to 6 centimeters (0.6 to 2 in) wide, with a base that is obtuse (blunt) to acute (pointed) and an acute tip. There are 3 to 5 pairs of pinnae, which are roughly deltate in shape and attach to the rachis via a long stalk. The final divisions of the blade are oblong to ovate, and the dark color of the axes extends into their base without forming a distinct joint. The blade tissue is bluish-green and somewhat leafy in texture, rather than thickly leathery. Veins are often visible on the upper leaf surface. A whitish (or rarely yellowish) powdery farina covers the underside of the blade, while the upper surface is free of hairs and powder, though it may bear a small number of glands. The edges of leaf segments curl back under to partially protect the sori, which grow along veins close to the leaf edge. The sporangia hold 64 spores, which are released during summer and fall. This species consists of sexual diploid plants with a chromosome number of 2n = 54. Argyrochosma dealbata is endemic to the United States. Its range extends from the western edge of Illinois south and west through Arkansas and Missouri to southeastern Nebraska, then continues south through Kansas and Oklahoma to Texas, with a separate isolated population in south-central Kentucky. It grows in crevices of calcareous rock cliffs or ledges. Kunze noted this species was suitable for cultivation, after growing it in a well-lit section of greenhouses in Berlin. George Schneider proposed it required "cool treatment", likely in contrast to desert-dwelling members of the same genus. It is described as preferring medium light, relatively dry, well-drained soil mixed with sand, which may have a high pH.
