Asplenium ceterach Linnaeus

Rustyback, Scale fern

Etymology The word ceterach comes from an Arabic word applied to the plant by Persian physicians
Description Rhizome: erect, branching, scales clathrate.
Frond: 15 cm high by 2 cm wide, evergreen, monomorphic, blade/stipe ratio: 8:1.
Stipe: green, from base all up the rachis, scaly, vascular bundles: 2 C-shaped, back to back, uniting to 1 upwards to an X-shape.
Blade: pinnatifid, lanceolate, leathery, deep green upper surface, scales dense, light brown, entirely covering the lower surface.
Pinnae: 6 to 12 pair, alternate; margins entire or sometimes irregularly crenate, slightly bending upwards, revealing the scales; veins netted, veins closing near the margins, not visible without removing the scales.
Sori: linear, along veins, indusium: vestigial, replaced by scales, sporangia: dark brown, maturity: late summer, then overwintering to maturity early .
Dimensionality: a rosette, fairly flat on the ground.
Culture Habitat: on limestone substrates. Distribution: maritime and southern Europe, northern Africa, east to the Himalayas. Hardy to -25°C, USDA Zone 5.
Distinctive Characteristics The densely scaly lower surface and the pinnatifid form make this unique. Demands a site with excellent drainage, and can withstand drying out in the manner of some polypodies.
Ceterach officinarum DC.
Asplenium ceterach
Asplenium ceterach. clockwise from top, habit (with A. trichomanes), plant in drought, scales, frond tip with scales removed on one pinna.  Illustration from Scandinavian Ferns by Benjamin Øllgaard and Kirsten Tind, Rhodos, 1993.

Asplenium ceterach , clathrate scale  BioImages: The Virtual Field-Guide (UK), photo © Malcolm Storey.
Asplenium ceterach
Asplenium ceterach. Two pinnae, scales removed on upper one to show venation and sori.  Illustration from Scandinavian Ferns by Benjamin Øllgaard and Kirsten Tind, Rhodos, 1993.
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