Links to genera Ferns and Horsetails (Monilophytes) Clubmosses and Quillworts (Lycophytes)
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| Asplenium ceterach • Rustyback Fern
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| Asplenium ceterach L.; Ceterach officinarum Willd.; Rustyback Fern
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A small tufted fern with linear-lanceolate or linear-oblong, pinnatifid, fronds, the rounded lobes alternating in a zig-zag fashion; deep green above, the underside densely covered with with scales that are silvery-white when young, turning reddish-brown; found on mortared walls and limestone rocks throughout much of the British isles, although commonest in the west and south west of Britain and throughout Ireland.
habit: plants grow in dense tufts from a short rhizome; the fronds are wintergreen and survive drought by curling up, when they become brown and appear dead, but recover quickly in wet weather.
size: generally 3-15cm in British plants, but up to 20cm in western Ireland.
leaf: deep, slightly greyish-green above (although paling to yellowish-green in very exposed sites) with a few scattered scales; underside thickly covered with overlapping scales (giving an initial impression of dense hairiness), silvery-white at first, becoming reddish-brown later; linear-lanceolate or linear-oblong, tapering somewhat at each end; pinnatifid, the lobes alternate, fully attached at the base and connected to the adjacent lobes, short, with rounded ends, entire or with rounded teeth (crenate); plants with crenate lobes are commonest in Ireland and to a lesser extent in south and west England and west Wales.
stipe: short, usually 1/4 as long as blade or less, covered with scales.
scales: on rhizome and lower part of stipe, dark brown to blackish, lanceolate, acuminate; on upper part of stipe a mixture of the former and scales similar to those on the underside of the blade and intermediate types; on underside of blade, ovate-acuminate, overlapping, silvery-whire when young turning reddish-brown later.
sori: linear, along veins, but mostly hidden by scales.
indusium: none, or only rudimentary.
spores: ripening April-October.
chromosome number: 2n=144, tetraploid.
identifying features: dense covering of scales on the underside of the leaves, strongly-alternate zig-zag lobes and tufted habit; a fern that once seen will not be confused with any other native species.
habitat: on limestone rocks, and mortared walls.
range: throughout Ireland; throughout much of Britain, but much less common in eastern counties and almost absent in northern Scotland.
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| Individual fronds, Oxfordshire, May. On left is old frond from previous year; on right is young frond from current year |
 | Individual fronds, Oxfordshire, May. On left is old frond from previous year with dehisced sporangia; on right is young frond from current year with unripe sporangia |
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| Detail of frond, upper surface, previous year's growth. Oxfordshire, May |
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Detail of frond, lower surface, previous year's growth, showing dehisced sporangia. Oxfordshire, May |
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| Plants on mortared limestone wall, Oxfordshire, May |
 | Plants on mortared limestone wall, Oxfordshire, May. Note the current year's fronds unfurling in the centre of the previous year's fronds. |
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| Plants on mortared limestone wall, Oxfordshire, May |
 | Plants on mortared limestone wall, Oxfordshire, May |
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| Plants showing effect of drought, Oxfordshire, July. They are still alive and will turn green again after rain. |
 | Another plant on the same wall. |
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