Argyrochosma nivea is an Andean fern species in the family Pteridaceae.
Description
The rhizome is short, thick, and more or less upright. It bears thin, delicate linear-subulate scales, 2.5 to 3 millimeters (0.098 to 0.12 in) long and of a uniform chestnut-brown color. The margins are entire (without teeth), or the walls of the marginal cells may project from the margin. The scales often become strongly crisped (wavy) when dried.
The leaves are 10 to 30 centimeters (3.9 to 12 in) long and arise close together from the rhizome. The stipe (the stalk of the leaf, below the blade) is slender, rounded, dull (rather than shiny), lacks hairs and scales, and varies from a bright to a dark chestnut-brown. It is typically shorter than to about as long as the leaf blade.
The leaf blades are lanceolate or deltate-lanceolate to ovate in shape, and tripinnate (cut into pinnae, pinnules, and pinnulets). The rachis (leaf axis) is similar in appearance to the stipe. It bears up to 12 pairs of pinnae, nearly opposite to one another, on stalks. They are ovate to lanceolate in shape. The pinnules are long and also borne on stalks. The pinnulets are broadly oblong to nearly orbicular (circular), obtuse (blunt) at the tip and truncate (abruptly cut off) to nearly cordate (heart-shaped) at the base, with entire margins. The dark color of the segment stalks stops abruptly at a joint at the base of the leaf segment. The segment at the tip of the pinnule is often lobed. The leaf tissue is leathery in texture, free of hairs and scales above and densely covered in white farina (powder) below.
In fertile leaf segments, the sporangia are close to the margin, borne along the further one-half to one-quarter of the secondary veins branching from the midrib of the segment. Each sporangium contains 32 spores. The tissue of the leaf margins retains the same texture as the rest of the leaf, and is not modified into a false indusium.
