Pityrogramma calomelanos  (L.) Link  1833

pronounced: pit-EYE-roh-GRAM-muh kal-oh-MELL-an-oss

(Pteridaceaethe maidenhair fern family)

common name: Silver Fern

Pityrogramma Pityrogramma calomelanossilver fern Pityrogramma calomelanos'beautiful black' stipeis derived from the Greek πιτυρον (pityron), bran, and γραμμη (grammé), a line, the stroke of a pen, referring to the colour and the arrangement of the sori; calomelanos is from καλος (kalos), beautiful, and μελας (melas), black, dark, referring to the colour of the stipes.

This terrestrial fern, native to the Americas from the Caribbean region south to Argentina, is now naturalized in many tropical parts of the world. It has an erect to shortly creeping rhizome, up to 1 cm in diameter, with light brown linear scales up to 4 mm long.

The fronds are sub-erect to erect, a darkish green in colour, glossy above, the abaxial surface with white waxy indumentum, rarely glabrous. The stipe, which turns a polished dark purple to black as the frond matures, is up to about 30 cm long, scaly on its lower part, but glabrous upward, and is, in its young stages, covered with a silvery-white powder. The laminae are oblong, with an acuminate apex, bipinnate-tripinnatifid, 15 – 30 by 8 – 15 cm. The rachis is grooved on the upper surface. The lateral pinnae are gradually smaller upwards; the lower ones are stalked, linear-subtriangular, acuminate to long-tailed at the apex, up to 10 by 2.5 cm; the pinna-rachis is slender, and grooved, with the grooves decurrent to those on the rachis; the pinnules are oblong to oblong-lanceolate, cuneate at the base, acute to acuminate at the apex, lobed or pinnatisect in larger ones.

Pityrogramma calomelanosunderside of frond Pityrogramma calomelanossporangiaThe sporangia are placed along veins throughout the lower surface, and are unprotected except for the revolute margin of the pinna.

The fern is usually found growing along the banks of new road cuts in sun, or on such places as retaining walls. More rarely, it is found in mesic or dry forest or shrubland, or in crevices on cliffs with associated native or introduced species. It is sometimes found as a weed in banana and pineapple plantations.

This plant is a hyperaccumulator of arsenic, and grows readily on arsenic-contaminated soils that are often found in abandoned mining areas. In parts of Nigerian and the Cameroons, it has appeared as a weed in palm oil plantations in the wet season, where weed growth has traditionally been controlled by arsenic-based herbicides. These are now losing their effect on the fern, presumably as it is able to absorb much of the arsenic without harming itself.

The ferns photographed were by the roadside through the housing development on Nobby Headland in Picnic Bay.

Photographs taken in Picnic Bay 2014

Page last updated 23rd January 2017

 

 

 

 

 

 

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