Acrostichum calomelanos L.; Gymnogramma ca/o-melanos (L.) Kaulf.

Naturalized Silver fern, silverback fern

Greek kallos (calo-), beautiful,+ melanos, black, probably referring to the lustrous dark stipes.

Rhizomes erect with dense mass of roots. Fronds clustered, to 95 cm long (mostly shorter), upright to somewhat spreading. Stipes densely clustered, reddish brown, shiny. Blades 2-pinnate-pinnatifid to 3-pinnate, subcoriaceous to chartaceous, adaxial ridges prominent and continuous with ridges of pinnae, abaxial surfaces with powdery, pure white farina, adaxial surfaces dull, dark green. Pinnae stalked. Pinnules lobed to again pinnate, those closest to rachis usually with auricles up to 2 mm long, tips more or less pointed. Sporangia dark, scattered along veins, when mature seen as dark lines through white farina.

Occasional in habitats similar to those of the gold fern but tending to favor more shade and moisture, sea level to 1,000 m, all major islands as well as Ni'ihau and Kaho'olawe.

This popular horticultural fern, native to Mexico, the West Indies, and south to Argentina, is now widely naturalized in the Tropics. It was first collected on O'ahu in 1908, but probably arrived at the same time as the more common gold fern.

The 2-pinnate-pinnatifid to 3-pinnate fern Pityrogramma calomelanos is the only fern in Hawai'i with white, waxy powder covering the entire undersurface of the pinnae.